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If you’ve just discovered you’re pregnant, it won’t be long before you hear about the "rules."

Don’t drink alcohol, avoid raw meat and sushi like the plague, give up hot tubs and hair dye or risk birth defects—the list can seem restrictive and overwhelming.

But is there any truth to these pregnancy myths that many expectant moms are subjected to?

Tracking Down the Evidence

Advice can differ among practitioners, as well as country to country due to wide-ranging governmental health guidelines and long-standing cultural beliefs.

On the hunt for some scientific evidence, June turned to Emily Oster, a professor of economics at Brown University who wrote Expecting Better while pregnant with her daughter Penelope.

The Harvard-educated Oster has applied her research skills to deconstruct the reasoning behind several well-known "mommy myths."

“A lot of the genesis for the book was in my own—and to an extent my friends’—frustrations with their experiences,” the mother of two explains.

“The central tension is between the pregnant woman and some broad pregnancy establishment that’s setting the rules.

“There’s a laundry list of things you should [avoid]—be it coffee or alcohol or smoking or soft cheese or sushi.

“Every culture has a different random set of things they’re not supposed to do, and there’s no ranking.

“How do I know which of these things is really bad and which is OK? And how do we know why they’re bad?”

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“I got pretty frustrated and confused about why there was not more understanding of the role of people’s preferences or any reference to data at all.

“The larger issue was this feeling that my autonomy was being compromised and no one was listening to the things that I might want and the fact that I’m a person.

“Part of the value of evidence is leveling the playing field for what’s not a good idea and what’s OK.”

Here, June assesses the evidence on four so-called pregnancy rules to help you make your own choices during this important time.

The Truth About…


The Rule: Just say no. Hong Kong’s Family Health Service advises avoiding all alcohol as it can "seriously affect your baby’s development."

Emily Oster’s Bottom Line:

Binge drinking can negatively impact your baby. Women can be comfortable with light drinking: one to two drinks a week in the first trimester; up to one drink a day in the second and third trimesters.

The Evidence:

Multiple studies confirm binge drinking during pregnancy can result in physical deformities and lead to cognitive problems known as fetal alcohol spectrum disorders (FASD).

The risk comes with drinking four or more drinks in a day, according to researchers from the U.K.’s University of Nottingham.

One study published in the British Journal of Obstetrics and Gynaecology actually shows that light to moderate drinking (consuming two to 10 standard drinks a week) is not a risk factor for the development of child behaviorial problems.

The exception is the first trimester, with mixed studies. A large Danish study in 2012 associated even low amounts of alcohol consumption with an increased risk of fetal death in the early months of pregnancy.

When you drink slowly, your liver processes most or all of the alcohol before it reaches the fetus.

If you drink quickly, your liver cannot cope and the toxins are passed to the baby across the placenta

Sushi's bad rap dates back to times when safety standards were more lax


The Rule: Avoid all raw fish as it contains Salmonella and Campylobacter, two strains of bacteria that can cause diarrhea, nausea and vomiting.

Emily Oster’s Bottom Line:

Don’t worry too much about sushi—it may carry bacteria, but these are no worse when you are pregnant than when you are not.

Be as sensible about the source of your raw fish as you would be pre-pregnancy.

The Evidence:

Improved safety standards mean that pregnant women no longer need to avoid food like sushi and sashimi, according to a report from the College of Family Physicians of Canada.

Illnesses caused by Salmonella or Campylobacter are not more likely during pregnancy. They also do not typically affect the fetus directly.

The exception to be aware of is Salmonella enterica, a strain of bacteria sometimes found in raw eggs that poses a high risk to a fetus.

Listeria (a bacteria) and Toxoplasma goudii (a parasite) are two common foodborne pathogens that can be damaging to your baby.

Listeriosis is associated with raw-milk/unpasteurized cheeses and deli meats. Toxoplasmosis is linked to raw/rare meat and poultry as well as unwashed fruit and vegetables.

Hair Dye

The Rule: Ditch the hair dye as it contains toxic chemicals that will affect the baby.

Emily Oster’s Bottom Line:

Don’t inject hair dye, but topical exposure to get rid of a few gray hairs or touch up your roots is fine!

The Evidence:

Some of the chemical components of hair dye (phenylenediamine, aminophenols and ethanolamine) have been found to increase birth defects and cause cancer when injected in high doses into rats.

Unless there are burns or abscesses on the scalp, the likelihood of these chemicals entering the bloodstream in humans is very limited.

They’re also unlikely to reach the placenta in substantial amounts or cause harm, according to a report by the Motherisk Team at the Hospital for Sick Children in Toronto.

Hot Tubs

The Rule: Stay out of hot tubs as the excessive heat can lead to birth defects.

Emily Oster’s Bottom Line:

Getting too hot in your first trimester—from a hot tub or hot yoga—can lead to an increased risk of neural tube defects. Cooler versions that do not exceed 38 C would be fine.

The Evidence:

Raising your body temperature above 38 C in the first trimester can lead to neural tube birth defects such as spina bifida and anencephaly, according to numerous studies.

This applies to getting a high fever as well as using a hot tub, saunas or electric blankets, reported researchers from the Texas Department of Health.

What about living in hot countries? There’s no evidence it causes birth defects, but one Spanish study did find unusually hot and humid days sent women into labor early—by about five days!

So what does the research tell us? That as pregnant women, we can make our own informed decisions!

Oster's conclusions have ruffled some mothers and experts with strong views in favor of following the so-called rules, and she's OK with that.

“I see some of the ultimate value of the book in giving you a launching point into having a more involved conversation with who’s treating you,” she says.

“There’s this attitude that the act of self-sacrifice somehow makes you a good mom, which I think is pretty counterproductive.

“There are some things which you should not do because you are pregnant, but there are a lot of other [restrictions] you’re just suffering for no reason.”