Marijuana Use During Different Times of Pregnancy Can Affect Growth of a Newborn

Marijuana use throughout pregnancy compared to use early on has the most significant impact on fetal growth, affecting newborn weight and head circumference. Though, the size of weight and circumference seem most affected when use of the drug is during different trimesters.

Data from a survey conducted by Central Michigan University College of Medicine found that newborn weight can be reduced somewhat by marijuana exposure even if it only occurs early in the pregnancy, while reduced head circumference was caused by exposure continued through the second trimester.

Published in Frontiers in Pediatrics in May, authors of the study suggest that women should be encouraged to avoid marijuana use at any point in pregnancy. Though, its recreational use has grown as 21 states plus Washington D.C have legalized recreational marijuana use in the past decade.

Legalization has resulted in increased concern, especially following research that has revealed many dispensaries recommending marijuana use to pregnant women to ease symptoms of pregnancy, especially morning sickness.

Previous studies have observed marijuana use and its effects on pregnancy and newborns, however, many questions remain unclear.

In this study, researchers wanted to examine whether the timing of marijuana use while pregnant negatively impacts fetal growth, and if these effects are global or specific to certain growth parameters.

To conduct this study, data was collected from electronic medical records of marijuana users (N=109) and a randomly selected control group of biochemically verified non-users (n=171). Given the known high rates of denial of substance use during pregnancy, researchers required self-report and biochemical confirmation of no use for non-users.

Alcohol and other drug use, including tobacco use, were eliminated as possible factors for differences between groups.

It was found that there was a significant decrease (p < .05) in newborn weight after marijuana use in the first trimester (−154 g) and throughout the pregnancy (−185 g) compared to non-users.

There was also a significant deficiency in head circumference following marijuana use in the first and second trimester only (−.83cm) and marijuana use throughout pregnancy (−.79 cm) compared to non-users.

Newborn length was not predicted by marijuana use.

Data found that most fetal weight gain and growth occurred in the third trimester with an estimated fetal weight velocity accelerating throughout pregnancy and peaking at 35 weeks pregnant. Researchers suggest this may be a potential reason for larger size deficits linked to late pregnancy, compared to early pregnancy exposure.

Authors note that low birth weight and decreased head circumference could result to neurological and psychological issues, health complications in childhood, and the development of various non-communicable diseases in adulthood.

Multiple studies suggest an increased risk of cognitive delay and neurodevelopmental disorders (including ADHD) among babies born at a low birth weight. In addition, low birth weight has also been associated with obesity later into adulthood with the possibility of early catch-up growth.

It’s noted that the sooner marijuana use is ended during pregnancy, the better chance a fetus has for normal growth and ultimately better child health and development.

There are several strengths to the study, one being the expansion of previous research by including timing of marijuana use during pregnancy.

Limitations include limited sample size, the chance of missing a drug exposure following patient denial and the limited window for urine drug screens. There was also no method to did not compare the total amount of substance being consumed.