Prenatal cannabis use was not significantly associated with cognitive, motor, or language development at age 2 in a large Canadian cohort, with an unexpected positive association with language in girls.
Parents, prenatal care providers, developmental researchers studying early childhood outcomes.
No significant developmental associations at age 2
What the researchers found
In 1,489 mother-infant dyads from the 3D prospective cohort, prenatal cannabis use (2.6% of women) showed no significant associations with cognitive (B=0.016), fine motor (B=0.029), gross motor (B=0.060), or language development (B=0.200) at age 2. An unexpected positive association between cannabis use and language development was found in girls only.
Why it matters
Concerns about prenatal cannabis effects on child development are widespread, but this large prospective study found no measurable impact at age 2. The use of clinician-administered developmental assessments rather than parent report strengthens the findings, though the majority of exposed women stopped after the first trimester.
The numbers in context
1,489 mother-infant dyads analyzed. 2.6% of women used cannabis during pregnancy. Most users stopped after first trimester. No significant associations with any developmental domain. Positive language association in girls only.
How the study worked
Data from 1,489 dyads in the 3D prospective pregnancy cohort (2010-2012). Prenatal cannabis use was measured via interviews each trimester. Child development was assessed using Bayley Scales of Infant and Toddler Development (BSID-III) for cognition and motor skills, and MacArthur-Bates Communicative Development Inventories for language at age 2. Multiple linear regressions with sex-stratified analyses were performed.
What this study cannot tell us
Self-reported cannabis use (no biomarker confirmation) likely underestimates true exposure. Only 2.6% reported use, limiting statistical power. Most users stopped after first trimester. Age 2 assessment may be too early to detect subtler cognitive effects. No measure of dose or potency.
How to read the evidence
Moderate: large prospective cohort (N=1,489) with validated clinical assessments, though self-reported exposure and early assessment age limit conclusions.
When this study was published
2025 study (data from 2010-2012)
The bigger picture
This study adds to mixed evidence on prenatal cannabis effects. The lack of association at age 2 does not rule out later-emerging effects, as some neurodevelopmental impacts may not manifest until school age. The low prevalence of use and early cessation in most users may also limit the ability to detect effects of heavier or sustained exposure.
Questions still open
- Would effects emerge at school age when cognitive demands increase? Would results differ with biomarker-confirmed exposure or in populations with higher-potency products? What explains the unexpected positive language association in girls?
Common questions
Did prenatal cannabis affect children's brain development?
Why was there a positive language association in girls?
Read the original research
Longitudinal Associations Between Cannabis Use during Pregnancy and Child Cognitive, Motor, and Language Development at 2 Years Old.
Maternal and child health journal, 29(4), 549-562
Citation
Pleau, Justine; Tanguay, Noémie; Courtemanche, Yohann; Séguin, Jean R; Herba, Catherine M; Simard, Marie-Noelle; MacLeod, Andrea A N; Fraser, William D; Muckle, Gina. (2025). Longitudinal Associations Between Cannabis Use during Pregnancy and Child Cognitive, Motor, and Language Development at 2 Years Old.. Maternal and child health journal, 29(4), 549-562. https://doi.org/10.1007/s10995-025-04077-8
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