Prenatal marijuana exposure was linked to smaller birth size even without tobacco use | Research

The takeaway

Among 325 pregnant women, marijuana-only exposure was associated with a 66% higher risk of small-for-gestational-age birth and more than double the risk of very small birth size, independent of tobacco use.

Obstetricians, midwives, prenatal care providers, and pregnant individuals using cannabis.

2.26x higher risk of very small birth size with marijuana-only exposure

What the researchers found

Marijuana-only exposure was associated with SGA <10th percentile (43% vs. 26%, aRR 1.66) and SGA <5th percentile (30% vs. 13%, aRR 2.26). Tobacco-only was associated with SGA <5th percentile but not <10th percentile. Co-use effects emerged in sensitivity analysis using cotinine-verified tobacco exposure.

Why it matters

This study used objective biomarker confirmation of marijuana exposure and separated marijuana from tobacco effects, providing clearer evidence that marijuana alone may restrict fetal growth.

The numbers in context

Sample: 325 mothers. Neither exposure: 46%. Marijuana-only: 11%. Tobacco-only: 20%. Co-use: 23%. Marijuana-only SGA <10th: 43% vs. 26% (aRR 1.66). SGA <5th: 30% vs. 13% (aRR 2.26).

How the study worked

Secondary analysis of the prospective LEAF cohort (2010-2015). Marijuana use assessed by urine THC-COOH testing, self-report, and medical records. Modeled as four exposure groups: co-use, marijuana-only, tobacco-only, and neither. SGA defined using 2017 US natality reference data.

What this study cannot tell us

Moderate sample size (325). High rates of co-exposure complicate separation of effects. Single urine sample may miss intermittent use. LEAF cohort may not be nationally representative.

How to read the evidence

Prospective design with biomarker-confirmed exposure, though moderate sample size limits precision.

When this study was published

Published in 2022 using data from 2010-2015.

The bigger picture

With marijuana increasingly perceived as safe during pregnancy, objective evidence linking it to fetal growth restriction is important for prenatal counseling.

Questions still open

Is there a dose-response relationship between prenatal THC exposure and birth size? Do the growth effects persist after birth?

Common questions

Does marijuana use during pregnancy affect birth size?

In this study, marijuana-only exposure was associated with a 66% higher risk of small-for-gestational-age birth and more than double the risk of being very small at birth.

Is the risk from marijuana or tobacco?

Both contribute independently. Marijuana-only exposure showed significant growth restriction even without any tobacco use, using objective urine testing to confirm exposure.

Read the original research

Association between Prenatal Marijuana and Tobacco Smoke Exposures and Small for Gestational Age at Birth.

American journal of perinatology, 39(16), 1726-1734

View on PubMed ↗Publisher’s paper ↗

Citation

Abdelwahab, Mahmoud; Klebanoff, Mark A; Venkatesh, Kartik K. (2022). Association between Prenatal Marijuana and Tobacco Smoke Exposures and Small for Gestational Age at Birth.. American journal of perinatology, 39(16), 1726-1734. https://doi.org/10.1055/s-0042-1753489