Impact of Cannabinoids on Fetal Growth Restriction
Fetal growth restriction (FGR) means a baby in the womb is not growing as expected, and cannabis does not treat it. In studies of pregnant people, THC exposure was linked with babies born small for their age. Whether to stop, change or keep anything you use is a decision to make with the clinician who manages your pregnancy.
Built on research published from 2002 to 2026: cohort studies in people, reviews, animal and laboratory work, read alongside the ACOG, SMFM, ISUOG and RCOG guidelines on fetal growth
Any product with THC
In a cohort of 3,435 women, a positive urine THC screen in pregnancy was linked with a small-for-gestational-age baby 1.69 times as often (95% CI 1.22-2.34) [1]. That is a link, not proof of cause.
CBD only
There are no studies of CBD-only products in pregnant people. In pregnant rats, CBD alone was followed by 10% lower fetal weight [2], and the FDA advises against CBD in pregnancy [3].
Smoke and vapor
Burning plant material and hot aerosol add their own load to the lungs, and many people who use cannabis also smoke tobacco. In one cohort, 41.7% of THC-positive women smoked cigarettes [1].
When an ultrasound says your baby is measuring small
Most people hear the words for the first time in a dim ultrasound room: “the baby is measuring a little small.” The sonographer moves on, the appointment ends, and the questions start in the car. How small? Is it serious? Did I do something?
A number without an explanation
Growth scans report a percentile, and a percentile sounds like a grade. It is not. It compares one estimate with many other babies of the same age in the womb, and the estimate itself can be off by a margin. One small measurement starts a process of watching, not a verdict.
Why the cannabis question comes up now
Pregnancy brings nausea that does not stop, nights without sleep and a lot of worry, and cannabis is easy to buy in many states. A review found that about 20% of pregnant people aged 18 to 24 use cannabis [4], and when researchers called Colorado dispensaries, about 70% recommended it for morning sickness [4]. Online advice runs from “totally natural” to “never,” which helps nobody decide.
The fear of being judged
Many people stay quiet because they worry about what their doctor will think, or what a hospital might report. That silence costs more than the conversation. ACOG advises obstetricians to ask every patient about substance use and to keep prenatal care open to anyone who answers honestly [5][6]. Clear facts, and one honest talk with your clinician, are the way through this.
What is on your mind right now?
Pick one; it opens the part of this page that answers it.
Is it serious? Many small babies are healthy and simply small; the scans that follow look for signs that growth has actually slowed. What FGR means and how it differs from a small baby.
I used cannabis. Studies in people link THC exposure with smaller babies, but they cannot tell you what happened in your pregnancy. What studies in people show.
Telling my doctor. Your clinician needs to know to plan monitoring well, and the rules on testing and reporting differ by state. Privacy, testing and state rules.
What is fetal growth restriction?
Fetal growth restriction is diagnosed when the estimated fetal weight (EFW) or the abdominal circumference (AC) on ultrasound falls below the 10th percentile for gestational age; below the 3rd percentile counts as severe FGR [7][8]. Behind that number is a simple idea: the baby is not reaching the size their own growth potential would allow, most often because the placenta is not delivering enough oxygen and nutrients [9].
The older name is intrauterine growth restriction (IUGR), and you will still see both. FGR is the term current US and international guidelines use [7][9].
What does “below the 10th percentile” mean?
How to read it: each dot is one baby of the same age in the womb, lined up from smallest to largest. Dark dots are the smallest ones.
10 of every 100 babies measure this small. Most of them are healthy and simply small; the scans that follow look for signs that growth has slowed.
3 of every 100 babies measure this small. At this size guidelines call FGR severe on size alone, and watching becomes closer [8][9].
FGR: fetal growth restriction
What it is: a baby in the womb who is not reaching their growth potential.
When it is named: during pregnancy, from ultrasound size, growth over time and blood flow [9].
What it tells you: the pregnancy needs closer monitoring and a planned delivery date.
SGA: small for gestational age
What it is: a size label, below the 10th percentile, without saying why [10].
When it is named: on a scan, or at birth from birth weight.
What it tells you: the baby is small; some SGA babies are growth restricted and many are healthy [9].
How common is it? By definition, about 1 in 10 babies measures below the 10th percentile on any chart, and only some of them have true growth restriction [9]. Of the babies who do, about 30% show it before 32 weeks (early FGR) and about 70% from 32 weeks on (late FGR) [9].
Quick answers
What is the abbreviation for fetal growth restriction?
What is fetal growth restriction called in Spanish?
Restricción del crecimiento fetal, or by its older name restricción del crecimiento intrauterino (RCIU). If you prefer to discuss your scans in Spanish, ask your clinic for an interpreter; medical interpreting is part of care, not a favor.
Can a baby be small and healthy?
Yes, often. Small parents tend to have small babies, and a baby who stays on a low but steady curve, with normal blood flow and amniotic fluid, is usually constitutionally small rather than growth restricted [9]. That is why one scan is rarely the last word.
How FGR is diagnosed: percentile, head circumference and Doppler
No single number makes the diagnosis. The sonographer measures the head circumference (HC), the abdominal circumference (AC) and the thigh bone, and a formula turns them into an estimated fetal weight. Those numbers are plotted on a growth chart; ACOG and SMFM recommend population charts such as Hadlock [8]. Then comes the part that separates a small baby from a struggling one: whether growth is slowing across scans, and what Doppler shows about blood flow.
Experts agreed on criteria in an international Delphi consensus, and both ISUOG and RCOG now use them [9][10]. The cut-off between early and late FGR is 32 weeks.
Compare early and late FGR
Pick one to see its criteria on their own.
| Criterion | Early FGR (before 32 weeks) | Late FGR (32 weeks or later) |
|---|---|---|
| Size alone is enough if | AC or EFW below the 3rd percentile, or absent end-diastolic flow in the umbilical artery [9] | AC or EFW below the 3rd percentile [9] |
| Otherwise, size plus | AC or EFW below the 10th percentile together with abnormal uterine artery or umbilical artery Doppler (pulsatility index above the 95th percentile) [9] | At least two of three: AC or EFW below the 10th percentile; a fall of more than two quartiles on the growth chart; cerebroplacental ratio below the 5th percentile or umbilical artery index above the 95th [9] |
| How it usually looks | Baby may be very small; Doppler changes progress step by step; often comes with preeclampsia [9] | Baby not necessarily very small; blood flow shifts toward the brain; harder to detect [9] |
| Main challenge | Timing birth: balancing the risks of staying in the womb against prematurity [9] | Finding it at all [9] |
You may also hear “stage 1.” Some hospitals grade FGR into stages from Doppler findings so that the next step is clear; stage 1 usually means size criteria are met and blood flow shows only mild changes. Ask which system your clinic uses, because the stages are not the same everywhere.
Symmetric
What it means: head and body are small in proportion.
Where you see it: older reports linked it to early causes such as genetic conditions or infection.
What the guideline says now: the pattern varies and does not predict outcome, so RCOG advises against using it to describe FGR [10].
Asymmetric (head-sparing)
What it means: the head circumference is relatively preserved while the abdomen is small, because blood flow is redirected to the brain.
Where you see it: more often with placental problems later in pregnancy [9].
What the guideline says now: the same RCOG caution applies; Doppler is the better guide [10].
Why your doctor orders a Doppler scan
A Doppler ultrasound measures how blood moves through vessels. In FGR it shows whether the placenta is under strain and how the baby is coping [9].
Umbilical artery Doppler
Middle cerebral artery (MCA) Doppler
Low resistance in the brain artery is the “brain-sparing” response: the baby sends more blood to the brain when oxygen runs short. It matters most in late FGR, where the umbilical artery can still look normal [9].
Cerebroplacental ratio (CPR)
The ratio of the brain-artery reading to the cord-artery reading. A low CPR picks up subtle redistribution of blood flow and is one of the Delphi criteria for late FGR [9]. In one small study of growth-restricted babies exposed to marijuana, an abnormal CPR went with more severe growth restriction, and 58.3% of that group had low amniotic fluid [11].
What causes FGR, including genetics
Doctors sort the causes into three groups: problems with the placenta, conditions in the mother, and conditions in the baby [10]. Placental dysfunction is the most common [9]. Often more than one cause works at once, and sometimes no cause is found.
Filter by type of cause
Pick a group, or keep all six cards in view.
Placental dysfunction
The spiral arteries of the uterus do not remodel properly, so the placenta gets less blood. This is the classic cause of early FGR [9].
High blood pressure and preeclampsia
About 70% of people with early FGR develop a hypertensive disorder, mainly preeclampsia [9]. Chronic hypertension, kidney disease, diabetes, autoimmune and heart conditions also raise risk [10].
Chromosomes and genes
Up to 20% of early FGR is linked with a chromosomal or structural problem in the baby, so a detailed anatomy scan is advised [8]. Chromosomal microarray testing is offered when FGR comes with an anomaly or extra fluid, or is unexplained before 32 weeks [8].
Placental mosaicism (CPM)
In confined placental mosaicism, some placental cells carry a chromosome change, sometimes involving a sex chromosome, that the baby does not have. It can restrict growth through the placenta alone. Ask a genetic counselor how a CPM result applies to your baby.
Infections and twins
Cytomegalovirus (CMV) is the infection most often tested for in unexplained FGR [8]. Twins and triplets grow on their own charts, and one twin can be restricted while the other is not.
Substances
Tobacco is the best-documented, and stopping smoking lowers the risk [10]. Alcohol, methamphetamine and other drugs also affect placental transfer [10]. THC exposure is linked with smaller babies in cohort studies [1][12].
The usual work-up, step by step
- Confirm the due date, ideally from an early ultrasound, so the percentile is calculated for the right week [9].
- A detailed anatomy scan, especially when FGR appears before 32 weeks [8].
- Doppler of the umbilical artery, and for late FGR the brain artery and the ratio between them [8][9].
- Blood pressure and urine checks for preeclampsia [9].
- Offer of genetic testing and infection testing when the picture is unexplained [8].
What could this mean for my pregnancy?
Thirteen short questions about your pregnancy, the scan and anything you use. Your answers stay on this page and show what to bring to your next prenatal visit, or whether you need care right now.
13 questions · about a minute · your answers stay in this browser
FGR guidelines compared: ACOG, ISUOG and RCOG Green-top
Three documents shape how FGR is handled. In the US, ACOG Practice Bulletin No. 227 [7] works alongside SMFM Consult Series #52 [8]; internationally, clinicians use the ISUOG Practice Guidelines [9]; in the UK, the RCOG Green-top Guideline No. 31, third edition [10]. They agree on most things and differ on a few, mainly the definition and the exact week for delivery. The full texts are free to read at the links in the sources.
Show one guideline
Pick one to read its column on its own.
| Question | ACOG-SMFM (US) [7][8] | ISUOG (international) [9] | RCOG Green-top No. 31 (UK) [10] |
|---|---|---|---|
| Definition | EFW or AC below the 10th percentile; below the 3rd is severe | Delphi consensus criteria; size alone counts only below the 3rd percentile | EFW or AC below the 3rd centile, or below the 10th with abnormal Doppler; Delphi criteria for early and late |
| Early vs late split | 32 weeks | 32 weeks | Before or from 32 weeks |
| Monitoring | Umbilical artery Doppler every 1-2 weeks, weekly if flow is reduced, 2-3 times a week if absent; weekly fetal heart rate testing | Several tests together: Doppler plus computerized fetal heart rate tracing or biophysical profile; early FGR in specialist units | Growth scans every 2 weeks; umbilical artery Doppler at diagnosis and at least every 2 weeks |
| Brain and other Doppler | Not suggested for routine management | MCA and cerebroplacental ratio central in late FGR; ductus venosus guides early FGR | Uterine artery Doppler at 18-23 weeks for high-risk pregnancies |
| Timing of delivery | 38-39 weeks if Doppler is normal; 37 weeks if below the 3rd percentile or flow is reduced; 33-34 if flow is absent; 30-32 if reversed | Late FGR: 36-37 weeks if cord Doppler is abnormal or size is below the 3rd percentile; 38-39 weeks with brain-sparing signs | Late FGR: birth started from 37 weeks and completed by 37 weeks 6 days; small babies without FGR features: around 39 weeks |
| Aspirin | Not recommended for the sole purpose of preventing FGR | Not part of these recommendations, which cover diagnosis and management | Daily aspirin from 12 to 36 weeks for those at risk of preeclampsia or placental dysfunction |
| Steroids before early birth | Recommended before 34 weeks, and up to 36 weeks 6 days in some cases | Recommended if birth is planned before 34 weeks | Recommended up to 35 weeks 6 days [10] |
This compares published documents; your care plan comes from your provider. For clinicians, The Obstetrics & Gynecology Project (OBG Project) summarizes the SMFM recommendations [13].
ICD-10 and CPT codes for FGR
These are the codes you are most likely to see on a visit summary, an insurance statement or a hospital record. They come from the ICD-10-CM code set published by CMS [14] and the CPT code set maintained by the AMA [15]. This is a reference for reading your paperwork, not coding advice; billing staff choose the final code from the full record.
Pregnancy codes for poor fetal growth end in a 7th character for the fetus: 0 for a single baby, 1 to 5 for each twin or triplet, 9 for other. There is no CPT code for “FGR” itself: what gets billed are the scans and tests used to watch it [15].
Filter codes
Tap a code to copy it.
| Code | What it describes | When it is used |
|---|---|---|
| Pregnancy record (ICD-10-CM) | ||
| Maternal care for known or suspected poor fetal growth, third trimester, single baby | Antepartum FGR after 28 weeks; O36.5910 and O36.5920 are the first and second trimester versions [14] | |
| The same, trimester not specified | When the record does not state the trimester [14] | |
| Newborn record (ICD-10-CM) | ||
| Newborn small for gestational age (a further digit gives birth weight) | Baby born below the expected size for age [14] | |
| Newborn affected by slow intrauterine growth, unspecified | Growth restriction noted without more detail [14] | |
| Newborn affected by maternal use of cannabis | When the baby’s clinician documents an effect of prenatal cannabis exposure [14] | |
| Ultrasound and Doppler (CPT) | ||
| Detailed fetal anatomy ultrasound | Recommended when FGR appears before 32 weeks [8] | |
| Follow-up ultrasound for growth and fluid, per baby | Repeat growth scans [15] | |
| Doppler of the umbilical artery | The main surveillance test in FGR [15] | |
| Doppler of the middle cerebral artery | Brain-sparing check, mainly in late FGR [15] | |
| Biophysical profile with non-stress test (76819 without it) | Checks of movement, tone, breathing and fluid [15] | |
| Substance use in pregnancy (ICD-10-CM) | ||
| Drug use complicating pregnancy, third trimester (O99.321 and O99.322 for earlier trimesters) | Paired with a code from F11-F16 for the substance [14] | |
| Cannabis use, unspecified, uncomplicated (F12.10 abuse, F12.20 dependence) | Names cannabis as the substance [14] | |
| Other stimulant use, unspecified, including methamphetamine | Names a stimulant as the substance [14] | |
A code on your record describes what was documented at a visit. It is not a judgment, and it does not by itself trigger a report to anyone.
Treatment and monitoring: can FGR improve?
There is no medicine that makes a growth-restricted baby grow normally in the womb. Bed rest, sildenafil and blood thinners have all been tried, and SMFM recommends against them for this purpose [8]. What works is careful watching and choosing the right moment for birth, so the baby is born before the placenta falls too far behind and not so early that prematurity adds its own harm [9]. ISUOG puts it plainly: in early FGR, delivery is the only effective therapy [9].
Here is what usually happens between diagnosis and birth:
- Growth scans about every 2 weeks, so the trend, not one number, guides decisions [10].
- Umbilical artery Doppler at diagnosis and then on a schedule set by the results, from every 1-2 weeks up to several times a week [8].
- Fetal heart rate tracing (non-stress test) or a biophysical profile, usually weekly once the baby could survive outside the womb [8].
- Blood pressure, urine and blood tests for preeclampsia, which often travels with early FGR [9].
- Steroid shots to mature the baby’s lungs if birth before 34 weeks is likely, and magnesium sulfate to protect the brain before 32 weeks [8].
- A planned delivery date, by induction or cesarean depending on Doppler, fetal tracing and your health [9].
Can FGR be reversed or go away?
Sometimes the label goes away: a later scan shows the baby back on a steady curve, and the first measurement or the dating turns out to be off. When the placenta is the cause, though, growth restriction does not reverse with treatment; it is managed until birth [9]. After birth, many growth-restricted babies catch up in size over the first years.
Aspirin: who it is for
Low-dose aspirin started early in pregnancy is prescribed to people at high risk of preeclampsia or placental problems, and it lowers the chance of a small baby in that group [10]. It is not a treatment once FGR is found, and SMFM does not recommend it for preventing FGR alone [8]. Take it only if your clinician prescribes it.
Is cannabis or CBD used to treat FGR?
No. No guideline uses cannabis, CBD or any cannabinoid to treat or prevent fetal growth restriction, and no study has tested it for that purpose. ACOG advises stopping cannabis in pregnancy [5], and the research on this page points the same way.
Complications and long-term outcomes
Most growth-restricted babies go home healthy, but FGR raises several risks, and knowing them helps you ask the right questions. The size of each risk depends on how early FGR started, how small the baby is and how early birth happens [9].
When do these show up?
Pick a stage of life, or keep all in view.
Stillbirth
Babies below the 10th percentile have a higher risk, and those below the 3rd the highest [9]. Finding FGR and timing birth well is how that risk is lowered.
Newborn problems
Low blood sugar, trouble keeping warm, jaundice and breathing problems are more common, especially with early birth [7]. Small babies often need closer checks in the first days.
Birth defects
FGR does not cause birth defects. It works the other way: some chromosomal and structural conditions cause poor growth, which is why the work-up includes a detailed anatomy scan [8].
Growth and feeding
Many babies catch up in size during the first year or two. Feeding plans and weight checks are part of early pediatric visits.
Development and learning
FGR is linked with a higher chance of developmental delay and lower school attainment, including in late FGR [9]. Studies link it with autism risk too, but they have not shown that FGR causes autism; prematurity and shared causes are part of the picture.
Heart and metabolism
Being born growth restricted is linked with more high blood pressure, insulin resistance, type 2 diabetes, heart disease and stroke in adulthood [9]. Healthy habits and regular checkups matter more for these children later.
Why cannabis comes up, and how it can reach the placenta
People reach for cannabis in pregnancy for the same reasons they reach for it at other times: nausea, poor sleep, anxiety and pain. Some were using it before they knew they were pregnant. And the product has changed: the average THC concentration in cannabis roughly doubled in under a decade.
THC crosses the placenta. The body has its own cannabinoid system, which helps with implantation and placental growth, and outside THC can interfere with it [4]. Researchers have followed four possible paths, all in animals or in lab cells:
Follow the path
Pick a step to see what the studies found there.
Uterine blood vessels
Oral THC or CBD oil disturbed the immune cells that remodel the uterine spiral arteries, so the placenta was set up with poorer blood supply [16].
Placenta cells
THC at 20 µM for 48 hours cut energy (ATP) production by 43.2% and slowed the cells that form the placental barrier and its hormones [17].
Nutrient supply
THC lowered the placental glucose carrier GLUT1 by 35% and left blood-vessel defects in the exchange layer of the placenta [18].
Baby’s brain blood flow
A synthetic cannabinoid given with alcohol reduced blood flow to the fetal brain, and the drop predicted which pups would die around birth [19].
These are lab and animal findings; they explain why researchers look, not what happens in a given pregnancy.
Is cannabis in pregnancy linked to FGR? What studies in people show
Yes, cannabis use in pregnancy is linked with smaller babies, and the link shows up in several cohorts. No study in people has shown that cannabis causes FGR, because no one can ethically assign pregnant people to use it: all the human data are observational, gathered by watching what happened. People who use cannabis in pregnancy also differ in tobacco use, income and stress, and those differences can explain part of the link [1][20].
| Level | What exists | What it can and cannot tell you |
|---|---|---|
| Trials in people | None. Randomly assigning cannabis in pregnancy would not be ethical. | Proof of cause is not available and is unlikely to be. |
| Cohort studies | Hospital and multicenter cohorts that compared exposed and unexposed pregnancies, using urine tests, newborn stool tests or self-report [1][12][21]. | Show a link with smaller babies; cannot fully separate cannabis from tobacco and other differences. |
| Reviews | A narrative review of human and animal findings on growth and metabolism [4]. | Summarizes other studies; adds no new data. |
| Animal and lab work | Mouse and rat pregnancies, and human placental cells [16][17]. | Explains possible mechanisms; doses and exposure differ from human use. |
How much more often did these outcomes happen after exposure?
How to read it: the dot is the study’s best estimate; the line is the likely range (95% CI); the gray line is “no difference”. A hollow dot means the study could not tell a difference.
Baby born small for gestational age
Other outcomes
Show as a table
| Outcome and comparison | Measure | Estimate (95% CI) | Study |
|---|---|---|---|
| Small for gestational age, THC-positive vs negative urine screen | Adjusted rate ratio | 1.69 (1.22-2.34) | Cohort, 2020 [1] |
| Small for gestational age, marijuana use vs none | Odds ratio | 5.16 (2.24-11.89) | Cohort, 2013 [20] |
| Preterm birth, THC-positive vs negative | Rate ratio | 1.06 (0.64-1.77) | Cohort, 2020 [1] |
| Major structural birth defects, THC-positive vs negative | Rate ratio | 0.58 (0.17-2.0) | Cohort, 2020 [1] |
| Abnormal 12-month social-emotional screen (ASQ-SE) | Adjusted rate ratio | 1.9 (0.92-3.91) | Cohort, 2020 [1] |
| Death within 1 year of birth, exposed vs unexposed | Odds ratio | 1.35 (1.12-1.62) | Narrative review, 2021 [4] |
The larger study followed 3,435 women in one health system; 283 of them (8.2%) had a positive urine THC screen [1]. The urban cohort was small, 166 low-income women, 39% of whom reported marijuana use, and it used a convenience sample with self-reported data [20], which is why its range is so wide. The death-in-the-first-year figure comes from a review that pooled other studies, so it carries the limits of those studies [4].
How many babies were born small?
How to read it: each bar is the share of babies born small for gestational age in one group of a multicenter study of 9,163 first pregnancies, 136 of them exposed to marijuana [12]. The choice of growth chart changes how many babies count as small, so both are shown.
In the same study, the growth curves of exposed babies began to fall behind at about 28 weeks, and the analysis was adjusted for tobacco [12].
Browse the studies yourself
Every study cited on this page, in plain words. Neutral results are included.
Urine THC screens, birth size and early development
A positive screen was linked with small-for-age birth (rate ratio 1.69); preterm birth, birth defects and the 12-month screen showed no clear difference [1].
Marijuana use, fetal growth and uterine artery Doppler
136 exposed pregnancies (1.5%); growth curves fell behind from about 28 weeks, and more exposed babies were born small on both kinds of chart [12].
Marijuana, placental weight and placental tissue
Among 224 stillbirths and 803 live births, about 4.45% used marijuana. In term stillbirths the baby-to-placenta weight ratio was lower with use (6.84 vs 7.8), while placental tissue looked no different [22].
Brain-to-cord blood-flow ratio in exposed, growth-restricted babies
Among babies exposed to marijuana, 13.5% had FGR; an abnormal cerebroplacental ratio went with more severe restriction [11].
Growth patterns and placental resistance in daily users
Third-trimester growth restriction was more common in daily marijuana users than in matched controls (p = 0.002); use was self-reported [23].
Partner violence, substance use and newborn outcomes
In low-income urban women, marijuana use was linked with small-for-age birth (odds ratio 5.16); 19% reported partner violence, a separate risk the study also tracked [20].
Detecting exposure in newborn stool, and the role of tobacco
Tested the baby’s first stool (meconium) to confirm exposure and looked at how tobacco used alongside cannabis affected newborn growth [21].
Metabolic effects of cannabinoid exposure before birth
Pulls together human and animal findings: higher THC potency, dispensary advice on nausea, and an odds ratio of 1.35 for death in the first year [4].
Oral THC or CBD oil and the uterine arteries
Fetal weight was 4.9% lower with THC, and offspring behavior changed [16].
CBD alone and the placenta
Fetal weight was 10% lower than in controls, with vessel defects in the placenta [2].
THC and symmetrical growth restriction
Fetuses were small in proportion, and the placental glucose carrier GLUT1 fell by 35% [18].
Alcohol with a cannabinoid and fetal brain blood flow
The combination raised blood alcohol by about 25% and reduced fetal brain blood flow, which predicted death around birth [19].
Omega-3 in the diet and THC-exposed offspring
DHA and EPA added to the mothers’ food eased THC-related growth restriction and heart changes in male offspring [24].
THC and the energy supply of placental cells
Energy production fell by 43.2% and the cells formed the placental barrier less well [17].
No studies of this type are cited on this page.
What kinds of studies is this evidence built on?
How to read it: each row is one kind of study, and the bar shows how many published studies on cannabis and fetal growth restriction are of that kind. People-based designs are at the top. Gray bars are animal, lab and commentary work, which cannot show what happens in a pregnancy.
Show as a table
| Design | Studies |
|---|---|
| Cohort studies | 17 |
| Case reports | 2 |
| Narrative reviews | 3 |
| Animal studies | 9 |
| Cell and lab studies | 3 |
| Who was studied | Studies |
|---|---|
| People observed, not treated | 23 |
| Whole populations | 4 |
| Cells and molecules | 5 |
| Not classified | 2 |
Animal studies are not data about people
Animal studies can do what human studies cannot: give a measured dose at a set time and look directly at the placenta. That is their value. Their limit is just as real. Rodents carry litters, pregnancies last three weeks, and the doses are given by injection or by tube in amounts that do not match how people use cannabis. Every result below happened in rats or mice.
Filter by substance
Pick one, or keep all five studies in view.
Oral THC or CBD oil
Given by mouth from early to mid-pregnancy in 65 mice, THC lowered fetal weight by 4.9% and disrupted spiral artery remodeling. Fewer pups were born alive in the THC group (13, against 38 in controls and 34 with CBD) [16].
CBD alone
In 12 pregnant rats, CBD was followed by 10% lower fetal weight (p = 0.0017) and vessel defects in the exchange layer of the placenta. The authors urge caution with CBD in pregnancy [2].
THC and symmetrical FGR
Fetuses were small in proportion (symmetrical FGR), and the placenta carried 35% less of the glucose transporter GLUT1 [18].
Synthetic cannabinoid with alcohol
In 40 pregnant mice, the combination raised blood alcohol by about 25% and cut blood flow to the fetal brain more than either alone. The brain-to-cord flow ratio predicted death around birth with 81% sensitivity and 85.7% specificity [19].
Omega-3 with THC
Omega-3 fats in the mothers’ diet eased THC-related growth restriction and heart-function changes in male offspring. The outcome is the offspring’s heart; this is not advice to take omega-3 [24].
Doses per kilogram in rats and mice do not translate to a human dose.
How these studies were done
Most of the rat studies injected THC or CBD into the abdomen (intraperitoneal injection), a route people do not use [18][2]. The mouse study of oral cannabis used a feeding tube at a high dose and studied human immune cells as a stand-in for the uterine ones [16]. The alcohol study used vapor chambers and a synthetic cannabinoid that is not in dispensary products [19]. The omega-3 study looked only at male offspring and did not test whether effects lasted into adulthood [24].
Does the form matter? Smoke, vapor, edibles, tinctures and creams
Cannabis is not only smoked. People vape it, swallow gummies and capsules, hold drops under the tongue or rub it on the skin. The human studies on fetal growth mostly did not record the form: they measured THC in urine or asked whether people used marijuana at all [1][20]. So no form has been shown to avoid the link with smaller babies. Each form has its own extra risks, and none is a safe substitute in pregnancy.
How is it used, or how would it be?
Choose the closest; most people combine more than one.
Specific to smoking
Joints, blunts, pipes and bongs burn plant material, and the smoke carries many of the same combustion products as tobacco smoke [3]. Blunts are wrapped in tobacco leaf, so they add nicotine as well. Smoke also reaches anyone else in the room.
Specific to vaping and dabbing
Dry-herb vaporizers, oil pens and cartridges avoid burning, but hot aerosol still travels the same airways. Concentrates used for dabbing, such as wax, shatter or rosin, are very strong, so the THC dose reaching the blood can be high.
Specific to edibles and capsules
Gummies, chocolates, drinks, capsules and swallowed oils avoid smoke, but THC still enters the blood after passing through the liver, and it crosses the placenta the same way. Effects start late and last long, so a second piece “because nothing happened” is a common mistake. The mouse study that found lower fetal weight gave cannabis by mouth [16].
Specific to tinctures and sprays
Drops under the tongue and mouth sprays skip the lungs, but they are absorbed into the blood, and part of each dose is swallowed. Many tinctures are made in alcohol.
Specific to topicals and patches
Creams and balms act mainly where they are applied, and no study has looked at them in pregnancy. Transdermal patches are different: they are designed to deliver cannabinoids into the bloodstream, so they count like any form that reaches the blood.
Specific to prescription cannabinoids
Dronabinol (Marinol, Syndros), nabilone (Cesamet) and cannabidiol (Epidiolex) are FDA-approved medicines with exact doses, prescribed by a doctor and filled at a pharmacy, not bought with a medical card. If you take one, do not stop on your own: ask the prescriber and your obstetric clinician together.
True of every form
- Whatever reaches your blood can reach the placenta.
- The studies in people did not separate forms, so no form is known to be safer for fetal growth.
- THC can add to the drowsiness of sleep aids, anti-nausea medicines and other sedating drugs.
- Product labels are not always accurate about THC and CBD content [3].
Choosing anything to use in pregnancy is a conversation for your clinician.
All forms as a table
| Form | What it avoids | What remains |
|---|---|---|
| Smoking | Nothing specific | THC in the blood, combustion products, often tobacco, secondhand smoke |
| Vaping & dabbing | Burning plant material | THC in the blood, hot aerosol, very strong concentrates |
| Edibles & capsules | Smoke and aerosol | THC in the blood, slow and long effect, risk of a repeat dose |
| Tinctures & sprays | Smoke and aerosol | THC or CBD in the blood, alcohol in some products |
| Topicals | Most absorption into the blood | No pregnancy data; label accuracy |
| Transdermal patches | Smoke, aerosol and swallowing | Cannabinoids in the blood, as with other forms |
| Prescription cannabinoids | Unknown product content | Effects of the drug itself; a decision for the prescriber |
CBD only, delta-8 and other products in pregnancy
Many people switch to CBD because it does not cause a high and feels gentler. A review notes that about 62% of CBD users take it for pain, anxiety or depression [4]. In pregnancy, though, there are no human studies of CBD-only products at all. What exists is animal work, and in pregnant rats CBD alone was followed by 10% lower fetal weight and placental vessel defects [2]. The FDA strongly advises against CBD, THC and marijuana in any form during pregnancy [3].
Filter by where the product comes from
Pick a group, or keep all in view.
| Product | What it is | What is known in pregnancy |
|---|---|---|
| Dispensary products | ||
| THC products | Flower, vapes, edibles and tinctures with THC as the main cannabinoid | Linked with small-for-age babies in cohort studies [1][12] |
| CBD products | High-CBD oils, gummies and creams | No human studies; lower fetal weight in rats [2] |
| THC + CBD products | “Balanced” products containing both | Carry what is known about THC; CBD does not cancel it out |
| Hemp-shop and gas-station products | ||
| CBD from hemp | Unregulated CBD oils, drinks and gummies | No human studies; may contain THC, pesticides or heavy metals [3] |
| Delta-8 THC and other isomers | THC variants made chemically from hemp CBD | No pregnancy data; intoxicating like THC, not FDA-evaluated, and made with chemicals that can leave harmful by-products [25] |
| Prescription medicines (FDA-approved, through a pharmacy) | ||
| Dronabinol (Marinol, Syndros) | Synthetic THC in capsules or liquid | Not studied for fetal growth; a decision for the prescriber with your obstetric clinician |
| Nabilone (Cesamet) | A synthetic cannabinoid in capsules | Not studied for fetal growth; same as above |
| Cannabidiol (Epidiolex) | Purified CBD for specific seizure disorders | The only FDA-approved CBD medicine [3]; never stop it without the prescriber |
Safety and interactions: alcohol, tobacco, blood pressure and medicines
Most of the study authors on this page give the same practical advice: stop cannabis and cannabinoids in pregnancy, and avoid combining them with alcohol [1][19]. Some risks below come from people, some only from animals; each is marked.
Filter by type of evidence
Pick one, or keep all in view.
Alcohol together with a cannabinoid Animal model
In pregnant mice, a synthetic cannabinoid given with alcohol raised blood alcohol by about 25%, worsened motor impairment and cut fetal brain blood flow more than either alone [19]. Alcohol is already a known cause of growth problems, so the combination is the one to avoid most.
Tobacco Studied in people
Tobacco is a cause of FGR on its own, and stopping helps [10]. Many people who use cannabis also smoke: 41.7% of THC-positive women against 5.9% of THC-negative women in one cohort [1]. Studies adjust for tobacco to separate the two [12], but the adjustment is never perfect. Using both means two sources of risk, not one.
Blood pressure and preeclampsia Studied in people
High blood pressure and preeclampsia are among the strongest causes of FGR, and about 70% of people with early FGR develop a hypertensive disorder [9]. The studies on this page did not test whether cannabis or CBD changes blood pressure in pregnancy, so neither should be used to manage it. Headache, vision changes and swelling of the face or hands need a same-day call.
Sleep aids and sedating medicines Studied in people
THC makes many people drowsy, and with antihistamine sleep aids, anxiety medicines or opioid pain relievers the effects add up. That raises the risk of falls, which matter more in pregnancy. Bring the full list of what you take, including over-the-counter products, to your next visit.
Anti-nausea medicines Studied in people
Nausea is the most common reason people turn to cannabis in pregnancy [4]. There are prescription options for nausea in pregnancy, and some of them are sedating, so adding THC on top can increase drowsiness. Ask your clinician what has been tried and what is left to try before you look elsewhere.
Placental cells and cannabinoid receptors Lab cells
In human placental cells, blocking the CB1 receptor fully prevented some of THC’s effects on placental hormones, and blocking CB2 prevented others [17]. This shows THC acts through the body’s own cannabinoid receptors in the placenta; it is a lab result, not a treatment.
What science doesn’t know yet
The gaps are large, and they are worth reading before drawing any conclusion about your own pregnancy. The researchers themselves list them.
- How much, how often and in what form people used cannabis is mostly unknown. Studies recorded “yes or no,” not dose or frequency [1][22].
- A urine test shows only recent use. Someone who used early in pregnancy and stopped can test negative and be counted as unexposed [1].
- Most human studies looked back at records from one health system, and some lost track of more exposed families than unexposed ones by the 12-month checkup [1].
- Self-reported use undercounts, so some “non-users” were probably users [22][23].
- Tobacco and other substances travel with cannabis, and statistics can only partly separate them [12].
- Small samples could not answer questions about specific birth defects or developmental delays [1][20].
- There are almost no human data on CBD-only products, delta-8, edibles, tinctures or creams in pregnancy.
- Animal studies used injections, feeding tubes, high doses or synthetic cannabinoids that do not match human use [2][16][19].
No data does not mean safe. It means nobody has measured it yet, and pregnancy is the time to choose the option with the fewest unknowns.
Your situation: where to start
The research is the same for everyone; the next step is not. Pick the description that fits you best, and the card shows what to say at your next visit.
Which is closest to you?
Pick one, or read all six below.
You used cannabis before you knew you were pregnant
This is very common, and it is not a reason to panic. Early exposure is one fact among many that your clinician weighs. Telling them helps them decide how closely to watch growth.
- Say roughly when you used, how often and in what form.
- Mention tobacco, alcohol or anything else used at the same time.
- Ask whether extra growth scans make sense for you.
You use it for nausea, sleep or anxiety
The symptom is real and deserves treatment. Stopping suddenly without a plan can leave you without relief, so the goal is a plan with your clinician, not white-knuckling it alone.
- Describe the symptom and how much it limits your days.
- Ask what pregnancy-tested options exist for it.
- Agree on what to do on the worst days.
Nausea · Insomnia · Anxiety (what is known outside pregnancy) · Prepare for your visit
You are planning a pregnancy
ACOG encourages people who are contemplating pregnancy to stop cannabis [5]. A preconception visit is the right place to plan how, especially if cannabis helps with a long-term symptom.
- Ask how long before trying to conceive to stop.
- Review every medicine for pregnancy safety.
- Ask about your own risk factors for preeclampsia and FGR.
Your baby has been diagnosed with FGR
Cannabis cannot help a baby grow, and if you still use it, stopping removes one factor you can control. The monitoring plan matters most now.
- Ask whether this is early or late FGR, and what the Doppler shows.
- Ask how often you will be seen and what would change the plan.
- Ask for the target delivery window.
You already have a medical card
A medical card, or its renewal, means a physician recommended cannabis for a condition at the time. It does not mean use in pregnancy has been approved. Talk with the clinician managing your pregnancy first; if your treatment plan changes, the physician who issued your recommendation should hear about it too.
- Tell your prenatal clinician about the card and the condition it covers.
- Ask how that condition will be treated during pregnancy.
- Check your state’s renewal rules before deciding anything about renewal.
You are a partner or family member
Support works better than pressure. Offer to come to appointments, help write down questions, and keep the home smoke-free: secondhand cannabis smoke shares harmful components with tobacco smoke [3].
- Ask how you can help, rather than checking whether they have stopped.
- Take over tasks on days when nausea or exhaustion is bad.
- Learn the warning signs below, so you can act on them too.
Prepare for your next prenatal visit
A visit goes better when the facts are on paper. Tap each item as you get it ready, then print the list or keep this page open in the waiting room.
What to bring
Questions worth asking
Privacy, drug testing and state rules
Fear of what happens after telling the truth keeps many people from saying anything. Here is what is generally true; the details depend on your state and your hospital, and this is not legal advice.
Is what I tell my clinician private?
Your health information is protected by the HIPAA Privacy Rule, which limits who your clinicians can share it with without your permission [26]. Information shared for your own treatment, between the clinicians caring for you, is allowed. ACOG recommends that obstetricians ask all patients about substance use as part of routine care [5].
Will I be drug tested during pregnancy or at delivery?
It depends on the state and the hospital. Some test only with a medical reason, some ask consent, and some test newborns after birth. ACOG recommends asking about use in conversation as a routine part of care [5]. The simplest way to know is to ask your clinician or the labor unit about their policy before delivery.
Will child protective services be told?
Reporting rules differ from state to state, and some states require clinicians to report substance use in pregnancy [6]. ACOG’s position is that seeking prenatal care should not expose a patient to criminal or civil penalties, and that fear of reporting should not keep anyone from care [6]. Ask your clinician how it works where you deliver.
Does a medical card protect me?
Not always. A card makes cannabis legal to buy and possess under your state’s program, but it does not necessarily change hospital testing policies or child welfare reporting rules. The rules for each program are on your state’s page.
What about drug testing at work?
Employment protections for card holders vary widely by state, and federal jobs and safety-sensitive roles follow federal rules. Check your state’s law and your employer’s policy before assuming a card covers you.
Talking to a physician: how an evaluation works
Start with the clinician who manages your pregnancy: they know your scans and your history. If you also want to talk through a medical cannabis plan, for example a recommendation you already hold or a condition you treated before pregnancy, a physician licensed in your state can review it with you one-on-one. That physician may recommend against cannabis while you are pregnant, and that is a normal, useful outcome of the appointment.
Fill in the intake form
Your state, your conditions, your medicines and that you are pregnant or planning to be.
See a physician licensed in your state
A one-on-one appointment, all online. You agree on the time with the physician; keep an hour free rather than a minute.
Get the physician’s decision
If the physician recommends medical cannabis, the signed recommendation arrives in your account. If not, you leave with the reasons.
Register with your state
Where required, you submit the recommendation to the state program, which reviews it and issues the card.
Across 250 reviews from patients in the states where we are licensed. We do not sort them by score and do not hide the low ones.
- 150,000+patients evaluated – everyone who has been through an appointment with us, in every state where we are licensed
- Since 2017doing only this: online evaluations for medical cannabis programs, and nothing else on the side
What happens after you book
You agree on the appointment time with the physician. Your documents stay in your account and documents, the price is shown before you pay, and how the medical card works explains the evaluation in detail. The physicians who see patients are listed on our physicians page.
Questions about fetal growth restriction and cannabis
Can fetal growth restriction improve?
Growth can look better on a later scan when the first estimate was off or the baby is simply small. When the placenta is the cause, FGR is managed with monitoring and a planned birth, not fixed in the womb [9]. See treatment and monitoring.
Can fetal growth restriction be reversed or go away?
No treatment reverses placental FGR; bed rest, sildenafil and blood thinners are not recommended for it [8]. After birth, many babies catch up in size over the first years.
How common is fetal growth restriction?
Can fetal growth restriction be misdiagnosed?
Yes. Ultrasound weight estimates have a margin of error, and a wrong due date shifts every percentile. That is why guidelines rely on growth over time and on Doppler, and why early dating scans matter [9].
Can fetal growth restriction cause autism?
FGR is linked with a higher chance of neurodevelopmental problems [9], and some studies also link it with autism, but a link is not proof of cause. Prematurity and the conditions behind FGR may explain part of it. For cannabis specifically, the 12-month social-emotional screen showed no clear difference (rate ratio 1.9, 95% CI 0.92-3.91) [1].
Can fetal growth restriction cause birth defects?
Can fetal growth restriction cause stillbirth?
FGR raises the risk, most of all below the 3rd percentile [9]. Monitoring and a timed delivery are designed to prevent it, which is why reduced movements always need a same-day check.
Does fetal growth restriction cause developmental delay?
It is linked with a higher chance of delay and learning difficulties, in both early and late FGR [9]. Most children with a history of FGR develop well; regular pediatric checks catch delays early, when help works best.
What is the abbreviation for fetal growth restriction?
FGR. The older term is IUGR, intrauterine growth restriction. SGA, small for gestational age, describes size only [7].
Is it safe to use CBD while pregnant?
That has not been shown. There are no human studies; in rats CBD alone lowered fetal weight by 10% [2], and the FDA advises against CBD in pregnancy [3]. See CBD and other products.
Is delta-8 different from THC in pregnancy?
Delta-8 is intoxicating like regular THC, is not evaluated by the FDA, and is often made with chemicals that can leave by-products [25]. There are no pregnancy data on it, so it should be treated as THC with extra unknowns.
Can a dispensary advise me during pregnancy?
Does a medical card protect me during pregnancy?
It makes purchase and possession legal under your state’s program, but it does not necessarily change hospital testing or child welfare reporting rules [6]. See privacy, testing and state rules.
Does the form of cannabis matter?
Smoke and vapor add airway and combustion risks, but edibles, tinctures and patches still put THC into the blood, and human studies did not separate forms. No form has been shown to avoid the link with smaller babies. See how the forms differ.
How does an online evaluation work if I am pregnant?
It is a telemedicine appointment: a physician licensed in your state reviews your history one-on-one, online, with nowhere to travel. Tell them you are pregnant in the intake form. They may advise against cannabis during pregnancy, and the price is shown before you pay. See how an evaluation works.
More research on cannabis and fetal growth restriction
This page cites a selection of studies. Our research library holds every study we track on cannabis and fetal growth restriction, from laboratory work to clinical trials, and lets you filter them by cannabinoid, study type and year.
- studies
- 35
- in people
- 27
- clinical trials
- 0
Share your experience
How this page was prepared and reviewed
This page summarizes published research on cannabis and fetal growth, read alongside the current fetal growth guidelines from ACOG, SMFM, ISUOG and RCOG. Every figure from a study carries a link to that study in the references below, and every clinical threshold links to the guideline it comes from. Studies in people and studies in animals are kept in separate blocks and labeled, so an animal result is never presented as a human one.
The content is reviewed by the Dr. Weedy medical team. We provide online evaluations for state medical cannabis programs, and this page does not recommend cannabis in pregnancy. It is education, not medical advice, and it does not replace prenatal care. If you see an error, tell us through the feedback form above and we will check it against the sources.
References
26 sources
- 1. Birth and early developmental screening outcomes associated with cannabis exposure during pregnancy. DOI: 10.1038/s41372-019-0576-6 PMID: 31911642
- 2. Cannabidiol Exposure During Rat Pregnancy Leads to Labyrinth-Specific Vascular Defects in the Placenta and Reduced Fetal Growth. DOI: 10.1089/can.2023.0166 PMID: 38364116
- 3. U.S. Food and Drug Administration. What You Should Know About Using Cannabis, Including CBD, When Pregnant or Breastfeeding. 2019.
- 4. Metabolic Consequences of Gestational Cannabinoid Exposure. DOI: 10.3390/ijms22179528 PMID: 34502436
- 5. American College of Obstetricians and Gynecologists. Marijuana Use During Pregnancy and Lactation: Committee Opinion No. 722. 2017.
- 6. American College of Obstetricians and Gynecologists. Substance Abuse Reporting and Pregnancy: The Role of the Obstetrician-Gynecologist. 2011.
- 7. American College of Obstetricians and Gynecologists. Fetal Growth Restriction: ACOG Practice Bulletin No. 227. 2021.
- 8. Society for Maternal-Fetal Medicine. Consult Series #52: Diagnosis and management of fetal growth restriction. 2020.
- 9. International Society of Ultrasound in Obstetrics and Gynecology. ISUOG Practice Guidelines: diagnosis and management of small-for-gestational-age fetus and fetal growth restriction. 2020.
- 10. Royal College of Obstetricians and Gynaecologists. Small-for-Gestational-Age Fetus and a Growth Restricted Fetus, Investigation and Care (Green-top Guideline No. 31). 2024.
- 11. Utility of the cerebroplacental ratio (CPR) in marijuana exposed growth restricted fetuses. DOI: 10.1080/14767058.2021.1983538 PMID: 34570659
- 12. Marijuana use, fetal growth, and uterine artery Dopplers. DOI: 10.1080/14767058.2021.1960973 PMID: 34470115
- 13. The Obstetrics & Gynecology Project. SMFM Recommendations: FGR Diagnosis and Management. 2020.
- 14. Centers for Medicare & Medicaid Services. ICD-10-CM code set. 2026.
- 15. American Medical Association. CPT (Current Procedural Terminology). 2026.
- 16. The impact of oral cannabis consumption during pregnancy on maternal spiral artery remodelling, fetal growth and offspring behavior in mice. DOI: 10.1016/j.ebiom.2025.105572 PMID: 39915201
- 17. Delta-9-tetrahydrocannabinol disrupts mitochondrial function and attenuates syncytialization in human placental BeWo cells. DOI: 10.14814/phy2.14476 PMID: 32628362
- 18. Δ9-tetrahydrocannabinol exposure during rat pregnancy leads to symmetrical fetal growth restriction and labyrinth-specific vascular defects in the placenta. DOI: 10.1038/s41598-019-57318-6 PMID: 31953475
- 19. Reduced fetal cerebral blood flow predicts perinatal mortality in a mouse model of prenatal alcohol and cannabinoid exposure. DOI: 10.1186/s12884-024-06436-9 PMID: 38605299
- 20. Intimate partner violence, substance use, and adverse neonatal outcomes among urban women. DOI: 10.1016/j.jpeds.2013.01.036 PMID: 23485028
- 21. Identifying prenatal cannabis exposure and effects of concurrent tobacco exposure on neonatal growth. DOI: 10.1373/clinchem.2010.147876 PMID: 20628142
- 22. Maternal Marijuana Exposure, Feto-Placental Weight Ratio, and Placental Histology. DOI: 10.1055/s-0040-1717092 PMID: 32971561
- 23. Effect of intrauterine marijuana exposure on fetal growth patterns and placental vascular resistance. DOI: 10.1080/14767058.2019.1683541 PMID: 31711334
- 24. Maternal dietary DHA and EPA supplementation ameliorates adverse cardiac outcomes in THC-exposed rat offspring. DOI: 10.1038/s41598-025-92844-6 PMID: 40064971
- 25. U.S. Food and Drug Administration. 5 Things to Know about Delta-8 Tetrahydrocannabinol. 2022.
- 26. U.S. Department of Health and Human Services. Summary of the HIPAA Privacy Rule. 2003.