But while some of those nutrients are important, there are many more that might be unnecessary, according to a new paper published in the British Medical Journal's Drug and Therapeutics Bulletin
It turns out that only folic acid and vitamin D have any evidence to support their use in dietary supplements for pregnancy, said Dr. James Cave, editor-in-chief of the bulletin and a practitioner at the Downland Practice in Newbury, Berkshire.
"I think we were surprised," Cave said. "Vitamin deficiencies are common in women of child-bearing age and you would therefore expect there to be plenty of good evidence that taking a multivitamin helps in some way."
Prenatal vitamins are often marketed as a way to get all of the vitamins and minerals an expectant mother and her unborn baby need that may not be provided in a daily diet. Prenatal supplements can cost as much as $16.64 per month in the United Kingdom, according to the paper.
"Women can be reassured that taking a folic acid supplement ... and vitamin D is all they need to do, and can save themselves a great deal of money not buying expensive branded multivitamins," Cave said. "If they have any specific concerns about a vitamin or mineral deficiency they should discuss this with their doctor or pharmacist."
Digging through the data
For the paper, dozens of previous studies, systematic reviews and individual trials were reviewed. The researchers examined the evidence available for supporting the use of folic acid, iron and vitamins D, C, E and A, among other nutrients, in prenatal supplements.
Many of the previous studies were carried out in countries where expectant mothers have poorer nutrition than in the United Kingdom, Cave said. The researchers aimed to focus on the needs of the United Kingdom population.
The researchers did not identify clear evidence that vitamins and nutrients other than folic acid and vitamin D helped to prevent birth complications
. Rather, the use of supplements containing vitamin A was not recommended during pregnancy.
The paper concluded that folic acid has the strongest evidence support, followed by vitamin D, which was less clear cut. "What we found was that the human is a tougher being than perhaps we realize and seems to be able to function completely well with some vitamin levels lower than are considered normal," Cave said.
What's recommended, what's not
However, some doctors are quick to point out that these findings are not representative of the needs of expectant mothers in the United States.
While the American Congress of Obstetricians and Gynecologists has no specific guidance about whether or not pregnant women need to take a prenatal vitamin, Dr. Scott Sullivan, a fellow at the group, said that taking specific evidence-based minimums of nutrients are suggested:
- 400 micrograms of folic acid
- 27 milligrams of iron
- 1,000 milligrams of calcium
- 600 international units of vitamin D
"It is certainly more convenient to take one supplement rather than five things and probably improves compliance," said Sullivan, an associate professor at the Medical University of South Carolina who was not involved in the new paper.
"It's not time to abandon the multivitamin or prenatal vitamin and it's not one size fits all," he said. "Nutrition is important in pregnancy, and should be maximized. The choice of prenatal vitamins should be individualized, made in conjunction with a woman's OB-GYN or provider, with attention to the minimums mentioned."
Even though doctors may have differing thoughts on the importance of supplements, many agree on what foods should be a part of a pregnant woman's diet.
For instance, a growing consensus is that cooked seafood
, such as salmon, tilapia or cod, is beneficial, Sullivan said.
"It's really interesting that women were scared of seafood because of mercury, which absolutely mercury is terrible, but that's a very small amount of what's available in seafood," Sullivan said. "There's conclusive evidence that for women who eat a regular amount of seafood during pregnancy, their children may have better performance on cognitive and motor tests."
Additionally, he recommends that pregnant women eat a balanced diet of fruits, vegetables, grains, proteins and dairy.