The deleterious effects of cannabis during pregnancy on neonatal outcomes.

OBJECTIVES: To evaluate whether cannabis use during pregnancy is associated with adverse neonatal outcomes that are independent of cigarette smoking. DESIGN: Prospective cohort study. SETTING: Adelaide (Australia), Auckland (New Zealand), Cork (Ireland), and Leeds, London and Manchester (United Kingdom). PARTICIPANTS: 5610 pregnant nulliparous women with low risk pregnancies recruited for the Screening for Pregnancy Endpoints (SCOPE) study, November 2004 - February 2011. At 14-16 weeks of pregnancy, women were grouped by self-reported cannabis use. MAIN OUTCOME MEASURES: Infant birthweight, head circumference, birth length, gestational age, and severe neonatal morbidity or mortality. RESULTS: 314 women (5.6%) reported using cannabis in the 3 months before or during their pregnancy; 97 (31%) stopped using it before and 157 (50%) during the first 15 weeks of pregnancy, while 60 (19%) were still using cannabis at 15 weeks. Compared with babies of mother who had never used cannabis, infants of those who still used it at 15 weeks had lower mean values for birthweight (adjusted mean difference [aMD], -127 g; 95% CI, -238 to -17 g), head circumference (aMD, -0.5 cm; 95% CI, -0.8 to -0.1 cm), birth length (aMD, -0.8 cm; 95% CI, -1.4 to -0.2 cm), and gestational age at birth (aMD, -8.1 days; 95% CI, -12.1 to -4.0 days). The differences for all outcomes except gestational age were greater for women who used cannabis more than once a week than for those who used it less frequently. CONCLUSIONS: Continuing to use cannabis during pregnancy is an independent risk factor for poorer neonatal outcomes.