In utero cannabis exposure linked to low birth weight and preterm birth in large study | Research

The takeaway

Among nearly 365,000 infants, in utero cannabis exposure was associated with 20% higher odds of low birth weight and 24% higher odds of small for gestational age, with dose-response relationships for these outcomes.

Pregnant individuals using cannabis, obstetricians, neonatologists

6.2% of pregnancies exposed

What the researchers found

After adjustment, in utero cannabis exposure was associated with low birth weight (aOR 1.20, 95% CI 1.12-1.28), small for gestational age (aOR 1.24, 95% CI 1.18-1.30), preterm birth <37 weeks (aOR 1.06, 95% CI 1.00-1.13), and NICU admission (aOR 1.06, 95% CI 1.01-1.11). Dose-response for low birth weight and SGA with increasing use frequency.

Why it matters

This is one of the largest studies examining cannabis and neonatal outcomes. The dose-response relationship for birth weight and SGA strengthens the evidence that cannabis exposure, not just confounding factors, contributes to these outcomes.

The numbers in context

364,924 infants, 22,624 (6.2%) cannabis-exposed. Low birth weight aOR: 1.20 (1.12-1.28). SGA aOR: 1.24 (1.18-1.30). Preterm <37 weeks aOR: 1.06 (1.00-1.13). NICU aOR: 1.06 (1.01-1.11). Early preterm <34 weeks aOR: 1.11 (1.00-1.23, p=0.055).

How the study worked

Population-based retrospective cohort of 364,924 singleton births at Kaiser Permanente Northern California (2011-2020). Cannabis exposure defined by self-report and/or positive urine toxicology. Models adjusted for demographics, other substance use, comorbidities, and prenatal care adequacy.

What this study cannot tell us

Observational design cannot prove causation. Cannabis use may be underreported. Cannot separate effects of smoking cannabis from THC itself. Some outcomes (preterm, NICU) had borderline significance.

How to read the evidence

Very large population-based cohort with objective exposure measurement, confounder adjustment, and dose-response analysis provides strong evidence.

When this study was published

2024 study of Kaiser Permanente data from 2011-2020

The bigger picture

The consistent finding of dose-response relationships across multiple studies and populations builds a compelling case that prenatal cannabis use has real, if modest, effects on fetal growth. The 6.2% exposure rate means a substantial number of pregnancies are affected.

Questions still open

Do different routes of cannabis administration (smoking vs. edibles) produce different neonatal risks? Is the birth weight effect clinically meaningful for individual infants?

Common questions

How much does cannabis affect birth weight?

Cannabis exposure was associated with 20% higher odds of low birth weight and 24% higher odds of being small for gestational age. The risk increased with more frequent use, supporting a dose-response relationship.

Were these effects independent of other substance use?

Yes. The analysis adjusted for other prenatal substance use, and sensitivity analyses further supported the associations, though some outcomes like preterm birth had borderline significance.

Read the original research

Neonatal outcomes associated with in utero cannabis exposure: a population-based retrospective cohort study.

American journal of obstetrics and gynecology, 231(1), 132.e1-132.e13

View on PubMed ↗Publisher’s paper ↗

Citation

Avalos, Lyndsay A; Adams, Sara R; Alexeeff, Stacey E; Oberman, Nina R; Does, Monique B; Ansley, Deborah; Goler, Nancy; Padon, Alisa A; Silver, Lynn D; Young-Wolff, Kelly C. (2024). Neonatal outcomes associated with in utero cannabis exposure: a population-based retrospective cohort study.. American journal of obstetrics and gynecology, 231(1), 132.e1-132.e13. https://doi.org/10.1016/j.ajog.2023.11.1232