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Coffee, Sex And Sushi: An Evidence Update On Pregnancy Do's And Don’ts

For pregnant women, Dr. Nathan Fox recommends an average of 20 to 30 minutes of moderate-intensity exercise four or five times a week. (il-young ko/Flickr)
For pregnant women, Dr. Nathan Fox recommends an average of 20 to 30 minutes of moderate-intensity exercise four or five times a week. (il-young ko/Flickr)
This article is more than 5 years old.

Most of Dr. Nathan Fox's patients have high-risk pregnancies. They may be having twins, or they’re dealing with complications such as high blood pressure or diabetes. Still, he spends a lot of time in his New York practice answering the little questions that seem to nag at nearly all expectant mothers:

Should I eat fish? What kind and how much? What about coffee? Or sushi? What if I forget to take my prenatal vitamin? Will I hurt my baby if I sleep on my back? If I go swimming? If I have sex? If I fly?

"There is so much misinformation that is given to women by the media, by things they read, by their friends, by their family -- obviously now with the internet, they’re finding stuff -- and even by doctors,” Fox says.

Add to that the societal pressure to do everything just right during pregnancy and the deep desire to make the best choices -- the right choices -- for their child, and it’s a distressing mix, he said.

To cut through misconceptions and to help other medical staffers put women’s minds at ease, Fox has written a paper based on the medical literature that answers the questions he hears most often, briefly and in lay language. Published this month by the journal of Obstetrics & Gynecology (widely known as “The Green Journal”), it distills the latest research on 19 topics and makes clear where data is lacking.

"This is a very balanced review," said Dr. Aviva Lee-Parritz, chief of the department of obstetrics and gynecology at Boston Medical Center.

The list includes some commonsense reminders, she said, including that pregnant women, like everyone else, should wear a seat belt. (The small potential risk to the developing baby from wearing one is outweighed by the significant risk of being in an accident without one.)

And, Lee-Parritz said, it counters some of the cultural messaging that pushes women to be overly restrictive during pregnancy.

Women looking for absolute answers won’t find many here. In most cases, readers still need to decide for themselves how much uncertainty they can manage. But Fox offers a concise tool to help — and definitely more reliable data than the commenters in that online pregnancy forum you’ve been trawling. The full article is here, but his main points include:

• Don’t worry if you miss a prenatal vitamin. Pregnant women need to be sure they get adequate amounts of folic acid, vitamin D, iron and calcium. If you have a healthy diet, a prenatal vitamin may not do much for you or your baby. Vitamin supplements are important for women who are undernourished. For those with a nutritious diet, it “is likely not required,” Fox writes.

• Avoid alcohol (but that one glass of wine is probably OK). Heavy drinking is clearly linked to problems in the fetus. But Fox points to several large studies that have found no link between a mother’s light or moderate drinking and developmental or behavioral problems in their children later in life.

"It doesn’t mean there are zero problems with it," Fox said. "It just means that we have never been able to find one." So what does he tell his patients who ask about having a glass of wine here and there? He can’t promise it’s perfectly safe, but it doesn’t appear to be dangerous.

• Do indulge in that morning coffee. Another beverage, another moral dilemma. Most data suggests that low-to-moderate caffeine consumption is safe, Fox writes.

Dr. Monica Mendiola, an OB-GYN at Beth Israel Deaconess Medical Center, said she tells her patients who are regular coffee drinkers that they can drink a cup of coffee daily or take a Tylenol to cope with the headaches they’ll have if they stop. Neither is harmful.

• Sure, have some sushi. And eat fish — the cooked kind — regularly, but avoid species that are high in mercury. Warnings against eating raw fish during pregnancy are mostly prompted by fear of parasites that are uncommon in developed countries and “are also not particularly dangerous,” Fox writes.

• Don’t do bed rest. Even if your grandmother says you need it, you almost certainly do not. Bed rest once was recommended for a wide variety of complications and concerns during pregnancy. The latest data shows it is not beneficial in preventing preterm birth or pregnancy loss, and it could be associated with risks, Fox writes.

• Do exercise. It’s good for you. Fox recommends an average of 20 to 30 minutes of moderate-intensity exercise -- that means you can still talk while doing it -- four or five times a week.

• Do feel free to get it on. For many women, there comes a point when you just can’t. You’re too big, too tired, too -- everything. But there’s no medical reason to avoid sex at any point in pregnancy, for most women.

Fox writes that it’s not clear whether sex could increase the risk of bleeding or infection in women who have vaginal bleeding or whose membranes have ruptured. And while there are no clear data to support it, doctors generally recommend that women whose cervix is covered by the placenta, called placenta previa, avoid sex after 20 weeks to prevent bleeding.

• Do travel, if you’d like. Air travel is safe while pregnant, Fox writes. Compression socks and getting up frequently is a good idea on longer flights. Whether (or when) to stop traveling as the end of pregnancy approaches -- and as the risk of some complications increases -- is an individual choice, to be weighed against the benefit of the trip, Fox writes.

As for the newer backscatter X-rays at security? No need to forgo them for a patdown, Fox said. The radiation exposure from the scan is about 1/600th the amount of cosmic radiation received during the flight itself.

• Don’t smoke cigarettes.
They’re not good for anybody. If you can’t quit entirely, then reduce smoking as much as possible, Fox writes. Nicotine replacement is acceptable for cessation. Vaping, sometimes used to quit cigarettes, may not be. There is not adequate research on vaping’s effect on pregnancy, Fox writes: “Logically, (electronic nicotine delivery systems) should not be more dangerous than smoking, but it is possible they are not as safe as other nicotine replacements such as patches and gum.”

• Marijuana is probably not a good idea, either. It is not linked to any adverse outcomes, but it also hasn’t been studied enough, Fox writes. Marijuana use among pregnant women has been growing in the United States. And some have used it to deal with nausea during pregnancy. Beth Israel's Mendiola said there are other ways of dealing with nausea. "Just because we don’t know what [marijuana] is causing, doesn’t mean it’s not causing harm," she said.

• Don’t panic when you wake up on your back. Many pregnant women go to bed each night with a pile of pillows and a mantra of “left is best” playing in their head. It’s thought that lying on the left side aids circulation to the baby and lying supine is linked to stillbirth.

But, Fox writes, the studies that made that link were limited because they were based on what women recalled about their past behavior, which can be imperfect. Plus, Fox writes, there’s no data that shows side-sleeping actually prevents stillbirths.

Mendiola said she hears often from women worried that they started out the night on their side and woke up on their back. Her response is simple: “That’s OK.”

Chelsea Conaboy is a freelancer who writes often about health care. Find her at and on Twitter @cconaboy. Photo via il-young ko via Flickr.



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