In March 2019 researchers from the USA published the results of their study to asses the association between infant birth weight and the use of cannabis during pregnancy. Information on cannabis use during pregnancy was collected using medical records with urine drug screens at the start of prenatal care and on delivery of the infant. Mothers who tested positive for other drugs during their pregnancy were excluded from the study. Results showed that babies born to mothers who took cannabis during their pregnancy tended to have a lower birth weight when compared to mothers who had tested negative. Cannabis use did not appear to have any effect on gestational age at birth although it did appear to increase the perinatal death rate.
Howard DS et al. Cannabis Use Based on Urine Drug Screens in Pregnancy and Its Association With Infant Birth Weight. J Addict Med. 2019 Mar 1. [Epub ahead of print]