Data Mixed with Respect to Cannabis and Preterm Birth Risk, Other Neonatal Outcomes

Columbus, OH: Newly published data exploring the relationship between maternal cannabis exposure and the risk of preterm birth (births prior to 37 weeks) shows inconsistent results.

In one recent study, published in the American Journal of Perinatology, investigators affiliated with the Ohio State University College of Medicine assessed the impact of self-reported cannabis use during pregnancy in 363 women at high risk of having a preterm birth. Authors determined, “Marijuana use was not associated with total preterm birth in this cohort, suggesting that among women already at high risk of preterm birth, marijuana does not increase risk further.”

Those findings are inconsistent with those of a separate paper published recently in the journal Pediatric and Perinatal Epidemiology. Researchers with John Hopkins University and the Boston University School of Medicine evaluated whether maternal cannabis use was independently associated with preterm birth and/or shorter gestational age in a cohort of 8,261 subjects. They reported that the concurrent use of cannabis and tobacco was associated with an increased risk of preterm birth, as was the use of marijuana alone if it was consumed in the final weeks of pregnancy. Maternal cannabis exposure was also associated with decreases in gestational age at birth. Authors acknowledged that prior studies on the subject have yielded mixed results and concluded, “Future studies need to confirm [these] findings before conclusions can be made regarding the risks of marijuana use a preterm birth.”

A third study, published by a team of British and Australian researchers in the Medical Journal of Australia, assessed the impact of cannabis use patterns on birth outcomes in 314 women. Investigators reported that the continued use of cannabis after 15 weeks of pregnancy was independently associated with “significant reductions in infant gestational age at birth,” as well as other adverse neonatal outcomes.

A fourth study, published in Nature: Journal of Perinatology, similarly identified an elevated risk of both preterm birth and shorter gestational age among marijuana-exposed newborns as compared to non-exposed controls. “[These] effects could not be attributed to other comorbidities, including other drug exposure and sociodemographic risks,” because the study “involved rigorous matching” of marijuana-using subjects and controls, authors wrote. Their findings, however, are inconsistent with those of another, similarly designed case-control study, recently published in The Journal of Maternal-Fetal & Neonatal Medicine. That study reported no significant differences in either birth weight or rates of pre-term delivery among mothers who used cannabis during their pregnancy as compared to those who did not.

Yet another study, published this month in the Journal of Maternal-Fetal & Neonatal Medicine, assessed both maternal and neonatal outcomes among women with hypertension in pregnancy. Researchers identified no differences in outcomes that could be attributable to cannabis exposure between users and non-users. They concluded, “Marijuana use in pregnancy was not associated with maternal or neonatal outcomes or worsened hypertensive disease among women with hypertension in pregnancy after adjusting for maternal characteristics.”

In May, a team of Columbia University researchers published a systematic review in the journal Frontiers in Psychology of 40 longitudinal studies assessing cognitive and developmental skills in marijuana-exposed offspring. That study concluded, “The [available] evidence [to date] does not support an association between prenatal cannabis exposure and clinically relevant cognitive deficits” later in life.

Additional information on maternal marijuana exposure and neonatal outcomes is available in the NORML fact-sheet.