A review and meta-analysis in JAMA Network Open revealed women exposed to marijuana in pregnancy were at significantly increased risk for adverse neonatal outcomes, including low birth weight, small for gestational age, and preterm delivery.
“Our research group noticed the publication of several new, high-quality studies on the use of marijuana in pregnancy,” said senior author Greg Marchand, MD, director of the Society of Laparoscopic Surgeons fellowship program in minimally invasive gynecologic surgery (MIGS) at Marchand Institute for Minimally Invasive Surgery in Mesa, Arizona. “It has also been a few years since a full analysis of all available data, so we decided it was time to see if the old conclusions still held.”
The authors searched PubMed, Medline, ClinicalTrials.gov, Cochrane, Scopus, and Web of Science databases from inception to August 2021. The analysis encompassed 16 studies and nearly 60,000 patients.1
There were significant increases in 7 adverse neonatal outcomes among women who were exposed to marijuana during pregnancy compared to those not exposed.
Marijuana users were over 2 times more likely to have an infant birth weight less than 2500 g (P = 0.005); 1.61 times more likely to have a small for gestational age offspring age (defined as less than the fifth percentile fetal weight for gestational age) (P < 0.001); 1.28 times more likely to incur preterm delivery (defined as before 37 weeks gestation), (P < 0.001); and 1.38 times more likely to have a neonatal intensive care unit (NICU) admission (P < 0.001).
Additionally, these women had a decreased mean birth weight with a mean difference of −112.30 g (P < 0.001); an Apgar score at 1 minute with a mean difference of −0.26 (P = 0.002); and infant head circumference with a mean difference of −0.34 cm (P = 0.02).
“We had not expected to see such a clear connection between preterm deliveries and lower birth weights,” Marchand told Contemporary OB/GYN.
Based on the review, there is now a very high level of evidence “to say that smoking marijuana during pregnancy is harmful, and we, physicians especially, can no longer state that we ‘just don’t know.’ This means that deciding to smoke marijuana during your pregnancy is also deciding to do something that can harm your baby,” Marchland said.
The review will also force some difficult decisions for mothers who use marijuana to treat medical issues, according to Marchand, who noted there may not be good substitute treatments for some conditions, especially chronic pain and anxiety. “This will set up a difficult ‘risk vs benefits’ situation, where these mothers, hopefully with the help of their physician, will have to decide if the risks of stopping marijuana outweigh the possible harm to the unborn baby,” he said.
Marchand advocates cessation for pregnant women who use marijuana for recreation only. “We don’t have the data yet to say how much you’d have to cut down in order to significantly reduce the risk, but using as little as possible definitely makes sense,” he said. “If you’re using marijuana to treat a medical condition, it is a good idea to discuss with your doctor if there is a different therapy you could use while you are pregnant. It would be preferable to have this clarified before you become pregnant to avoid exposing the unborn baby.”
The review is just the beginning, according to Marchand. “We need some well-designed, longer-term trials to tell us what, if anything, marijuana is truly doing to these children down the road,” he said. “It was fairly simple to correlate birth weight and preterm delivery to smoking marijuana in pregnancy, but to draw the connection to developmental and behavioral disorders years down the road, that will be tricky.”