Adding Cannabis to Alcohol During Pregnancy Increases Risk of Small Babies | Research

The takeaway

Among pregnancies with alcohol diagnoses, co-occurring cannabis use was associated with 21% higher risk of small-for-gestational-age infants, while adding tobacco raised preterm birth risk by 44%.

Pregnant individuals, OB-GYNs, substance use counselors, and perinatal epidemiologists

What the researchers found

Compared to alcohol alone, co-occurring alcohol+cannabis increased SGA risk (aRR=1.21); alcohol+tobacco increased extreme/very preterm birth (aRR=1.44), late preterm (aRR=1.25), and SGA (aRR=1.31); all three substances had the highest extreme preterm risk (aRR=1.68).

Why it matters

This is one of the first large studies to isolate cannabis's additive effect on birth outcomes beyond alcohol — showing that polysubstance use compounds risk in measurable, clinically significant ways.

The numbers in context

California births 2007-2021; alcohol+tobacco: aRR=1.44 extreme/very PTB, 1.25 late PTB, 1.31 SGA; alcohol+cannabis: aRR=1.21 SGA; all three: aRR=1.68 extreme/very PTB, 1.29 SGA.

How the study worked

Population-based retrospective cohort linking California birth certificates (2007-2021) to maternal/infant hospitalization records, using ICD-9/10 codes for substance use diagnoses with adjusted risk ratio analysis.

What this study cannot tell us

ICD codes may undercount substance use; cannot determine dose, timing, or frequency; California-specific population; unmeasured confounders possible despite adjustment.

How to read the evidence

Large population-based cohort using 15 years of linked administrative data with adjusted analyses, though limited by ICD-based exposure ascertainment.

When this study was published

Published in 2026 with 2007-2021 California data, spanning both pre- and post-legalization periods.

The bigger picture

Prenatal substance use rarely involves just one substance — understanding how combinations multiply risk is essential for targeted screening and intervention during pregnancy.

Questions still open

Does cannabis alone (without alcohol) carry similar SGA risk? At what gestational period is polysubstance exposure most harmful?

Common questions

Does cannabis make alcohol more dangerous during pregnancy?

Yes — this study found that adding cannabis to alcohol during pregnancy increased the risk of having a small-for-gestational-age baby by 21%, and adding tobacco made risks even higher.

Which substance combination is most risky during pregnancy?

All three together (alcohol, tobacco, and cannabis) carried the highest risk — 68% increased risk of extreme preterm birth compared to alcohol alone.

Read the original research

Adverse birth outcomes in alcohol-exposed pregnancies with or without tobacco and cannabis.

Preventive medicine, 202, 108427

View on PubMed ↗Publisher’s paper ↗

Citation

Anunziata, Florencia; Frankeberger, Jessica; Baer, Rebecca J; Chambers, Christina; Bandoli, Gretchen. (2026). Adverse birth outcomes in alcohol-exposed pregnancies with or without tobacco and cannabis.. Preventive medicine, 202, 108427. https://doi.org/10.1016/j.ypmed.2025.108427