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Prenatal vitamins are a staple of modern pregnancy.  But a report out Monday in the journal Drug and Therapeutics Bulletin suggests they don’t make much difference in preventing complications such as premature birth, low birth weight, and stillbirth.

The nitty gritty:

The journal reviewed dozens of clinical trials testing the effect of several vitamins and nutrients commonly included in prenatal supplements. Some of the trials were quite large, with up to 24,000 participants. 

The review found no clear evidence that vitamin C or E supplements helped prevent stillbirth, low birthweight, preterm birth or pre-eclampsia. It further suggested that vitamin A supplements could be harmful to a pregnancy, and that iron should not be routinely prescribed for pregnant women because of side effects such as constipation.

What they’re saying:

Prenatal supplements packed with nutrients are an “unnecessary expense,” the researchers wrote.

“Pregnant women may be vulnerable to messages about giving their baby the best start in life, regardless of cost,” they wrote.”The marketing of such products does not appear to be supported by evidence of improvement in child or maternal outcomes.”

The trade group that represents supplement makers disagreed, pointing out that pregnant moms need to be sure they’re getting a slew of nutrients beyond those the researchers studied, including calcium, iodine, and protein. The group, the Council for Responsible Nutrition, said dissuading mothers-to-be from taking supplements — like those sold by some of its member companies — “could lead to serious repercussions.”

You’ll want to know: 

The researchers do recommend that pregnant women take vitamin D and folic acid supplements, both of which are available in inexpensive generics. And they call for more attention to a healthy overall diet.

But keep in mind:

The review focuses mostly on the babies, not their mothers, said Dr. Hyagriv Simhan, a professor of maternal and fetal medicine at University of Pittsburgh Medical School.

He pointed to iron as one example. “Having normal iron at the time of delivery reduces the need for blood transfusions, and it helps prevent some of the effects of maternal blood loss during childbirth,” he said.

Simhan also questioned the study’s emphasis on the need for vitamin D supplements, saying there’s not a lot of evidence behind that recommendation.

The obstetrician also said that he would likely continue recommending prenatal multivitamins to his patients. “It’s really hard to get a pregnancy-appropriate level of nutrients through diet alone,” he said.

The bottom line:

Many ingredients in prenatal supplements don’t appear to be necessary to support fetal health, but women should consult with their obstetricians about their particular needs.

This story has been updated with comments from the Council for Responsible Nutrition.

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