MATERNAL CANNABIS USE AND BIRTH-WEIGHT - A METAANALYSIS

Aims. To estimate the effect of maternal cannabis use on birth weight. Design. Meta-analysis of published observational studies adjusted for cigarette smoking. Separate analyses were performed for studies of lo w birth weight and mean birth weight. We used fixed and random effects models, but in all cases the results were identical. Setting. From th e Medline database, we identified 10 studies in which the results were adjusted for cigarette smoking. In seven studies, information on cann abis use was collected prenatally. Five studies reported results for d ifferences in mean birth weight associated with maternal cannabis use. Participants. 32483 women giving birth to live-born infants. Measurem ents. Mean birth weight and odds ratio for low birth weight. Findings. Three analyses of the studies on mean birth weight were conducted to avoid double-counting women from one study. The largest reduction in m ean birth weight for any cannabis use during pregnancy was 48 g (95% c onfidence interval (CI) 83-14 g), with considerable heterogeneity amon g the five studies. Mean birth weight was increased by 62 g (95% CI 8 g reduction-132 g increase; p heterogeneity 0.59) among infrequent use rs (less than or equal to weekly) whereas cannabis use at leastfour ti mes per week had a 131 g reduction in mean birth weight (95% CI 52-209 g reduction; p heterogeneity 0.25). From the five studies of low birt h weight, the pooled odds ratio for any use was 1.09 (95% CI 0.94-1.27 , p heterogeneity 0.19). Conclusions. There is inadequate evidence tha t cannabis, at the amount typically consumed by pregnant women, causes low birth weight.