Caffeine. Alcohol. Raw eggs. Deli meat. Tuna. Unpasteurized cheese.
The list of restrictions can get pretty long. But how many of these things should we really be worried about while pregnant?
Many of the food-related restrictions are pretty standard and your care team can help you figure out which ones are most important for you.
But what about hair dye? Or hot yoga? Or cat litter? Or gardening?
That’s where we turn to Emily Oster’s book “Expecting Better” to guide us.
“Pregnant women are told to avoid cold cuts, sushi, alcohol, and coffee without ever being told why these are forbidden,” says the publisher. “Moms-to-be desperately want a resource that empowers them to make their own right choices.”
During her own pregnancy, Emily (an award-winning economist) looked into the research. She found many of the rules of pregnancy are misguided or plain wrong.
We’ve excerpted the top tips about restrictions from Expecting Better to share with you here.
- Hair Dye
“The primary concern with hair dye is that toxic chemicals in the dye will affect the baby. In very high doses, some of the chemical components of hair dye can increase birth defects in rodents. They can also cause cancer (again, in rats). This is a concern in principle, of course, but it is something of a stretch to compare the impact of directly injecting the pregnant rat with high doses of chemicals every day during pregnancy to three or four incidents of topical exposure (which is what you get from actually dyeing your hair).
Human studies have generally not shown any association with an increased risk of birth defects. Although a couple of small studies have suggested a link with childhood cancer, later and larger studies have not confirmed this. Overall, the rat evidence doesn’t seem to translate into a human link.
In addition to birth defects and cancer, one study comparing Swedish hairdressers to the rest of the Swedish population showed a small but statistically significant increase in low birth weight babies among the hairdressers. Since hairdressers work with hair dye more than the average person, this finding led to the concern that perhaps at high doses hair dye affects birth weight. In the end, this finding wasn't supported by other studies and it seems likely the result is driven by other aspects of the job (for example, the fact that hairdressers spend all of their time standing up).
There are a number of detailed reviews of this issue, and they all argue pretty compellingly that there is no reason to worry about hair dye use any time in pregnancy.
In fact, even the American Congress of Obstetricians and Gynecologists suggests it's fine after the first trimester. To be fair, I think you probably should avoid injecting yourself with hair dye during the first trimester (or, really, at any time). Getting rid a few grey hairs, or touching up your roots, is a different story.”
The verdict: Dye away! Concerns about hair dye are overblown.
- Hot Tubs, Baths & Hot Yoga
“It turns out that at least some hot yoga is frowned upon during pregnancy. This is for the same reason that very hot baths or extended periods in hot tubs are verboten: it has been suggested that raising your body temperature during the first months of pregnancy can lead to birth defects. Some evidence for this comes from a 2011 study. The authors identified about 11,000 babies with birth defects and 7,000 without. They compared their mothers’ behavior during pregnancy and looked at whether the mothers of the babies with birth defects were more likely to use hot tubs during early pregnancy.
The authors considered seventeen birth defects. For two of them (an intestinal problem called gastroschisis and a neural tube defect called anencephaly) they found an association with hot tub use. On its own, it is a little hard to draw confident conclusions from this. Maybe these findings just showed up by chance since the authors were testing so many outcomes. However, other studies found the same effects on neural tube defects. This connection is supported by animal studies which can be done in a more controlled environment (researchers randomly heat up some pregnant animals and not others).
All together [sic], this makes it seem quite likely that elevated temperature in the first trimester increases the risk of birth defects like spina bifida and anencephaly. This means that anything that elevates your temperature increases that risk: fever, hot tub use, very hot baths and, yes, hot yoga.
It's probably important to note: the real concern is about an increase in body temperature to above 101 degrees or so. Hot tubs are typically about 105 degrees, as is Bikram Yoga. Spending time working out in a 105-degree environment can increase your body temperature. But a cooler hot tub, or a cooler version of hot yoga (some are only 85 or 90 degrees) would be fine. In addition, the neural tube defect concern is limited to the first trimester; by the end of that period, neural tube formation is complete.”
The Verdict: Skip these. Getting too hot during your first trimester can lead to an increased risk of neural tube defects like spina bifida.
- Cat Litter
“When I got pregnant I received a large number of emails (from my mother, my friend Nancy, etc., etc.) with dire warnings about the cat: "Do not clean the litter box!" Sometimes multiple exclamation points.
My doctor was kind of dismissive about this concern ... The worry about cat litter is toxoplasmosis. If that sounds familiar, it should: it comes up in the context of food restrictions: most common source of toxoplasmosis is uncooked meat. Recalling the discussion there: if you have been exposed to toxoplasmosis before pregnancy, there is no cause for concern. But if you are exposed for the first time during pregnancy, it can be dangerous for the baby, causing low IQ, vision problems, or death.
Although uncooked meat is the primary source of toxoplasmosis, it is also possible to get it from cat feces. If your cat has been eating uncooked meat, that is.
Despite the cat litter emphasis, the circumstances under which you can get this from a cat are fairly specific. Cats are infected by eating something (like raw meat) which gives them the parasite. The first time they are exposed they excrete the parasite eggs in their feces for several weeks; you can be infected through exposure to these. Once they are exposed once, they typically acquire immunity and are not exposed again. This means you’re at risk if you’re exposed to a cat during their first exposure. If your cat is old, even if they live outside, they probably have already had this.
Perhaps for this reason, cat litter is not the main source of toxoplasmosis infection. In fact, in many studies it’s not even a significant source of infection ... The one caveat to this is that you may want to be a little careful if you get a kitten for the first time while pregnant, especially if you feed it a lot of raw meat. In fact, one study in the US did find that owning three or more kittens (although not owning one or two) was associated with higher toxoplasmosis rates…
Somewhat surprisingly: although cat litter seems to have little risk, there is significant toxoplasmosis risk from gardening. That study in Europe which was reassuring on cats did find a strong association between toxoplasmosis and working with soil. This suggests that if you are planning to garden while pregnant you should use gloves, and possibly consider a mask to avoid inhaling any particles…”
The Verdict: Changing cat litter is probably fine, but skipping gardening during your pregnancy might be wise.
For more conventional wisdom-breaking info, grab a copy of Expecting Better for yourself.
Excerpts above from Expecting Better by Emily Oster, Penguin Random House, 2019.
About Emily Oster
Emily Oster is an American economist and bestselling author. She currently holds the rank of Professor of Economics at Brown University. Her research interests span from development economics and health economics to research design and experimental methodology. She is the author of two books, Expecting Better and Cribsheet, which discuss a data-driven approach to decision-making in pregnancy and parenting.