Prenatal THC Exposure Linked to Smaller Babies Who Then Grow Rapidly | Research

The takeaway

Babies exposed to THC in the womb had less body fat at birth but then grew rapidly, with breastfeeding potentially stabilizing the growth pattern.

Prenatal care providers, perinatal researchers, parents who used cannabis during pregnancy

THC-exposed babies had 95g less fat at birth but grew rapidly afterward

What the researchers found

Among 128 mother-child pairs, prenatal THC exposure (12% of children) was associated with 95g less fat mass and 2.1% lower adiposity at birth, followed by rapid postnatal growth (0.42 BMI z-score increase per square root year). Shorter breastfeeding duration amplified this pattern, with 1.1 higher BMI z-score by age 3.

Why it matters

The pattern of being born small then growing rapidly is associated with metabolic problems later in life. This study identifies a specific cannabinoid-driven growth trajectory that could have long-term health consequences.

The numbers in context

128 pairs, 15 (12%) THC-exposed, 3 with concurrent CBD. THC associated with -95g fat mass (95% CI: -174 to -14), -2.1% adiposity (CI: -4.2 to -0.4). Rapid growth: +0.42 BMI z-score/sqrt year. Short breastfeeding: +1.1 BMI z-score at age 3.

How the study worked

Prospective cohort following 128 mother-child pairs through 3 years, with mid-gestation urinary THC and CBD measurement, neonatal body composition assessment, and longitudinal BMI tracking.

What this study cannot tell us

Small sample with only 15 THC-exposed children limits statistical power. Urinary measurement captures recent use rather than cumulative exposure. Breastfeeding may also transfer THC, complicating the protective finding. Only followed to age 3.

How to read the evidence

Prospective design with objective biomarker exposure measurement, but very small exposed group limits statistical confidence.

When this study was published

2025 study with follow-up through age 3.

The bigger picture

Born-small-then-grow-fast is a well-known risk pattern for later obesity and metabolic syndrome. If prenatal THC creates this trajectory, it has implications for the growing number of pregnancies with cannabis exposure.

Questions still open

Does the rapid growth pattern persist beyond age 3? Does breastfeeding help by stabilizing growth or is it a proxy for other factors? Would these children face higher metabolic risk later in life?

Common questions

Does using cannabis during pregnancy affect the baby's growth?

This study found THC-exposed babies had less body fat at birth but then grew rapidly in the first three years. This born-small-then-grow-fast pattern is associated with metabolic health risks later in life.

Does breastfeeding help THC-exposed babies?

Breastfeeding appeared to stabilize growth patterns in THC-exposed infants. However, since breast milk can also contain THC, the researchers note that the impact of lactational exposure needs further investigation.

Read the original research

Impact of prenatal exposure to delta 9-tetrahydrocannabinol and cannabidiol on birth size and postnatal growth trajectories.

Pediatric obesity, 20(1), e13187

View on PubMed ↗Publisher’s paper ↗

Citation

Moore, Brianna F; Mueller, Noel T; Perng, Wei; Sauder, Katherine A; Hébert, Emily T; Hoyt, Adrienne T; Wymore, Erica M; Boyle, Kristen E; Su, Emily J; Shapiro, Allison L B; Kinney, Gregory; Sempio, Cristina; Klawitter, Jost; Christians, Uwe; Dabelea, Dana. (2025). Impact of prenatal exposure to delta 9-tetrahydrocannabinol and cannabidiol on birth size and postnatal growth trajectories.. Pediatric obesity, 20(1), e13187. https://doi.org/10.1111/ijpo.13187