A recent study by Oxford Academic states that Cannabis use while conceiving may be associated with reduced fecundability. The study involved 1228 women, who were followed for up to six cycles while trying to conceive, as well as throughout pregnancy if they conceived. The women ranged from 18 to 40 years old and had a history of pregnancy loss. Each woman provided up to four urinary metabolite measurements, during preconception and early pregnancy, to measure reproductive hormones and identify early pregnancy losses. Cannabis use was measured using a biomarker and a self-report assessment.
The study showed that approximately 42% of marijuana users became pregnant throughout the study, compared to 66% of women who didn’t use the drug. While marijuana users had reduced fecundability, there also were associated with having increased frequency of intercourse per cycle, and a higher Luteinizing hormone (LH) to Follicle Stimulating Hormone (FSH) ratio. There were no relations noted between preconception cannabis use and pregnancy loss, likely due to the study’s limited sample size. The self-reporting measures of the study may also have underestimated cannabis use, due to the stigma associated with it. Regardless, the findings of the study emphasize the importance of further research to note the effects of the drug on reproductive health.
There are a few possible mechanisms that are causing the underlying effects of Cannabis on fertility—
First, some evidence suggests the drug may inhibit the release of the Gonadotropin hormone-releasing hormone (GnRH). GnRH, a tropic peptide hormone, is a key regulator of the reproductive axis. It is released from the hypothalamus and stimulates the pituitary gland to produce LH and FSH, both essential to female reproductive health. With loss of GnRH, there will be an imbalance with the reproductive hormones, and loss of regulation with ovulatory function, uterine receptivity, and implantation. This is supported by the high LH to FSH ratio noted in the study. In addition, there have been animal studies, especially with rhesus monkeys, that offer significant support for this mechanism by showing the impact of cannabis disruption on the hypothalamic pituitary gonadal (HPG) axis and the consequent alteration of GnRH levels.
Second, there is a likelihood that impaired endocannabinoid signaling decreases uterine receptivity. The Endocannabinoid system is composed of CB1 and CB2 receptors, which are dispersed throughout the brain and other regions of the body. CB1 receptors are especially highly expressed in the uterus, and are integral to several female reproductive events such as preimplantation embryo development, oviductal transport, and ultimately implantation in the uterus. With the use of Cannabis, the increased concentration of bound CB1 receptors may have embryotoxic effects that influence implantation.
Third, the impaired endocannabinoid system may affect sperm transport in the female reproductive tract and fertilization.
With the increasing normalization of marijuana use today, there has been an increased use of the drug during pregnancy, especially between 2009 and 2016. While this specific study hasn’t established a strong association between the drug and fertility, it’s important to recognize the association and possible mechanisms involved and to continue to stay well informed on the effects of the drug.
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