Once a woman becomes visibly pregnant, it isn't long before she's being asked extremely personal questions by complete strangers:

"Are you going to have an epidural or go natural?

"You're not drinking alcohol, are you?"

"Have you tried ginger for your morning sickness?"

Often, such questions are followed up with unsolicited advice based on folk wisdom or anecdotes.

Myths and folklore about pregnancy, labor and delivery abound. They persist in part because of the difficulties in conducting properly controlled scientific studies on pregnant and breast-feeding women and their newborns. In particular, researchers are loath to test medicines on pregnant women in the wake of the thalidomide disaster.

Much of the advice women get is relatively harmless — abstain from alcohol, caffeine and sex — but because of the research gap, it often isn't backed up by rigorous scientific study. Putting women on bed rest to prevent miscarriages is a prime example: There's very little evidence of effectiveness, yet it persists in medical practice for lack of better, research-based treatment options. "Pregnancy and birth are two of the greatest unknowns in science," says Tonia Moore-Davis, director of the nurse-midwife practice at Vanderbilt University School of Nursing in Nashville.

Such recommendations can seem like benign ways of ensuring a healthy pregnancy and baby, but the pressures on women pile up: Eat only the best foods (or your baby won't like broccoli later), gain weight in a very narrow range (or your child will be diabetic and obese); breast-feed exclusively for six months (even if you have to go back to work in six weeks).

In the last year, however, several studies or reviews of studies have looked carefully at popular pregnancy recommendations, and what they've found turns some of the folk wisdom on its head. Here's a look at what scientific evidence can really tell us — or not — about five topics in pregnancy, labor and delivery. Knowing what the science says gives women the chance to make their own informed decisions instead of relying on Internet rumors, kaffeeklatsch gossip and well-meaning, but sometimes uninformed, advice.

No good options for morning sickness

Though it's not a life-threatening condition, nausea associated with pregnancy is exhausting and miserable and can cause major losses in productivity. Unfortunately, research into effective treatments is lacking.

"It's seen as a 'normal' sign of pregnancy. But most women do suffer the effects of it, and the psychological effect can really get to people," says Anne Matthews, a midwife and lecturer of nursing at Dublin City University in Ireland. She's noticed more women turning to therapies such as acupressure, ginger and vitamin B6. "But there's a need for evidence. We don't really know if these are safe or effective."

Curious, she and a team of researchers reviewed the scientific literature to see which morning-sickness treatments had been tested in randomized, controlled trials. They found only 27 studies since 1959 that met the criteria. Treatments included acupuncture, acupressure, ginger, vitamin B6 and anti-nausea drugs such as hydroxyzine, thiethylperazine and doxylamine combined with B6. The review, published in September by the Cochrane Library, found that none of the remedies had enough scientific evidence behind them to be deemed effective.

"We were disappointed," Matthews says. "I'd prefer to have a clearer message. But there just isn't enough strong, reliable evidence to say whether things don't work or do work."

Her regretful recommendation to nauseated women: "Strictly speaking, I would have to say, nothing."

Sex during pregnancy is safe for most

It is one of the most common questions obstetricians get from patients: When is it OK to have sex during pregnancy?

"Many patients and their partners are afraid about having sex," says Dr. Claire Jones, a resident physician in obstetrics and gynecology at Mt. Sinai Hospital in Toronto. "People turn to the Internet for this kind of information, and the things you can read there are ridiculous."

Yet from a review she co-authored (published in January in the Canadian Medical Assn. Journal), the findings were clear: "For healthy women who have an otherwise healthy pregnancy, there is no reason not to have sex and enjoy it."