Do Alcohol and Marijuana Affect Egg Quality?

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I’m wondering about how my choices in the period of egg development (i.e., 90 days before conception) affect fetus health and the ultimate health of a baby. I listened to a podcast about the use of alcohol and cannabis edibles, though the studies weren’t referenced. While there were comments on correlation with miscarriage, fetus development/baby health is tangentially referenced without much info, and it’s freaking me out. Can you outline any science or study-debunking evidence on these impacts, if any?
—Your Faithful Reader

Citations are very important. Not to soapbox too much, but one of the primary goals of ParentData is to be as transparent as possible about why I think some studies are better than others, and about where data is (or is not) enough to make some conclusion.

On these particular topics, I’ve written pretty extensively about alcohol in Expecting Better and elsewhere (with many citations). Excessive drinking during the period right around conception does seem like it can be linked with not conceiving (see, e.g., this study in Denmark). I am not aware of any evidence that alcohol consumption in the pre-pregnancy period has any causal relationship with any baby outcomes.

For cannabis, the conversation is more complicated for a few reasons. First, the data isn’t as good. Use of cannabis is more selected, even than use of alcohol, partly because it’s historically been illegal. We’re starting to get some more evidence on cannabis use during pregnancy, and the landscape is complex (I wrote more about that here).

In terms of use before pregnancy, the primary concern — indeed, the only concern I have really seen in the academic literature on it — is that marijuana use will lower fertility. In animal models, the active component THC lowers fertility (libido, sex drive, etc.); those are experimental data. In people, we see correlations between heavy marijuana use and lower sperm count; that data is mostly observational, so it’s not as airtight as the animal models, but it seems like a plausible link.

Actual research on the impact on fertility is less obvious in the data. The best evidence I could find on this is from a study that followed couples as they tried to conceive and surveyed them about marijuana use. It did not find any association between marijuana use and fertility for either men or women. A more recent study found a small negative relationship between regular cannabis use and infertility, although the research design was less convincing.

It seems possible that there are impacts on fertility that are small enough that we do not pick them up in these data; it’s an open research area. What I will say is that I cannot find any evidence to support the claim that using marijuana preconception would cause birth defects.