Recent studies on the effects of marijuana use have shown wide-ranging positive effects on health, including aiding in the treatment of cancer and other debilitating diseases such as diabetes. It is important to keep in mind, however, that most of these positive effects occur in adults. Marijuana use during pregnancy and early childhood has more commonly been associated with a litany of negative health consequences to both mother and child – both pre- and post-natal.

Marijuana is still considered dangerous for childhood use. Although some evidence of seizure treatment in children has been seen, significant decrease in cognitive and motor functionalities have also been observed in habitual underage cannabis consumers. The instance of accidental ingestion of marijuana by children has also seen a slight uptick since legalization.

Marijuana use during pregnancy is still widely devoid of tangible research compared to the volumes of research performed on post-natal children and adults. The instance of marijuana use during pregnancy is seemingly overlooked as a fringe consequence of legalization. Because of this, the risk of the prevalence of marijuana use during pregnancy is much higher than that of the risk of cigarette or alcohol use. Ironically, tangible results of the consequence of only cannabis use during pregnancy are often confounded by concomitant cigarette and alcohol use.

Nonetheless, studies on the effects of marijuana use during pregnancy are beginning to be published. Like any newly studied issue, some results are conflicting. Most research confirms, however, that marijuana use during pregnancy leads to increase in preterm birth, maternal asthma, and even lower-than-average birth weight.

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Marijuana Use During Pregnancy: Not Recommended

Gestational Consequences

A study published online April 30, 2016 and appearing in the July 2016 issue of Reproductive Toxicology shows a five fold increase of spontaneous preterm birth (SPTB) in 5500 women researched who used marijuana before, up to, and beyond 20 weeks gestation¹.

In Table 1 (below), the predicted length of gestation is exponentially decreased in relation to the number of marijuana uses up to 20 weeks, and linearly decrease in relation to the number of marijuana uses up to 15 weeks. Note that ceasing of marijuana use prior to 15 and 20 weeks gestation leads to slightly longer gestation periods overall than continuing to use marijuana through these periods. This is true for both minimal (<50 times marijuana used) and heavy (200+ times of marijuana use) marijuana consumption.

decreased gestation due to marijuana use during pregnancy
Marijuana use is associated with decreased gestation. Courtesy: Science Direct

As a reference, a ‘normal’ human gestation period is 40 weeks, but can vary between 37 and 42 weeks. So, while marijuana use during pregnancy does show decreased gestation, it does not show a decrease to the point of prematurity.

Surprisingly, the effects of marijuana use on SPTB were shown by the study to be rapidly diminished if marijuana use during pregnancy was stopped prior to the 20 week gestation cutoff. Ceasing of marijuana use prior to 20 weeks gestation led to a similar rate of premature birth equal to that of no marijuana use, whatsoever. The study did not go so far to say marijuana use is ‘safe’ up to 20 weeks gestation, but the results suggest minimal risk of premature birth/decreased gestation when ending marijuana use prior to 20 weeks gestation.

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An alternative study published in the May 4 issue of Biology of Reproduction shows similar results². Researchers submitted mice to continuous excessive cannabinoid flooding of the CB1 receptor in the placenta. Mice subjected to cannabinoid flooding showed increased instance of stillborn pups as opposed to wild type mice. Lead researcher Chen Sun, et. al determined the increase in stillborns to be influenced by increased levels of p38 protein kinase, which is activated by cannabinoid receptor CB1. Down regulation of cannabinoid flooding showed less instance of stillborn pups in affected type mice, confirming the researcher’s results.

Maternal Consequences

While marijuana use during pregnancy can lead to premature birth, low birth rate, and undocumented prenatal mental issues, harm does not extend only to the growth of the baby. A study published in the January 2016 issue of the American Journal of Obstetrics and Gynecology links marijuana use during pregnancy to an increase in maternal asthma³. Table 2 (below) shows the results of the study published. The ‘Adjusted OR’ column indicates a high instance of maternal asthma in patients research who used marijuana during pregnancy. The small ‘p’ value (p = 0.001) indicates little to no result interference due to undocumented variables or environmental pressures.

marijuana use during pregnancy table
Table 2 – Maternal asthma risk increased with marijuana use during pregnancy. Courtesy: AJOG

Confounding Results?

Like the research subjects, themselves, research on the effects of marijuana use during pregnancy is very much in its infancy. A study of nearly 8200 women published September, 2015 in the very same American Journal of Obstetrics and Gynecology indicates that when results of a study on marijuana use during pregnancy were adjusted for body mass index (BMI) socioeconomic status/index (SEI), and other drug use including tobacco, the results showed no statistical significance between marijuana use and premature birth4.

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A simple explanation of the conflicting results from the very same source could be indicated in the women tested in both groups. In the study published in September, 2015, women were of a variety of ethnic backgrounds, where as in the studies published in the AJOG in January 2016 as well as in Reproductive Toxicology, subjects tested were nearly 90% Caucasian³,4.


1. Chabarria K, Racusin D, Sachs M, Suter M, Mastrobattista J, Aagaard K. 126: To inhale or not to inhale: a descriptive study of marijuana use and its effects in pregnancy from a contemporary large, population based cohort. American Journal of Obstetrics and Gynecology. 2016;214(1):S86-S87. doi:10.1016/j.ajog.2015.10.162.

2. Gerhardt K. WORLD OF REPRODUCTIVE BIOLOGY: Marijuana Exposure May Affect Pregnancy Outcomes. Biology of Reproduction. 2016. doi:10.1095/biolreprod.116.141168.

3. Leemaqz S, Dekker G, McCowan L et al. Maternal marijuana use has independent effects on risk for spontaneous preterm birth but not other common late pregnancy complications. Reproductive Toxicology. 2016;62:77-86. doi:10.1016/j.reprotox.2016.04.021.

4. Conner S, Carter E, Tuuli M, Macones G, Cahill A. Maternal marijuana use and neonatal morbidity.American Journal of Obstetrics and Gynecology. 2015;213(3):422.e1-422.e4. doi:10.1016/j.ajog.2015.05.050.