Most pregnant women do not need to be screened for vitamin D deficiency, nor given additional supplements, according to an official statement issued by the American College of Obstetricians and Gynecologists.

Vitamin D provided by the mother's body helps build a baby's bones and teeth before it's born. Vitamin D is manufactured in the skin in response to sunlight and occurs naturally in some foods, as well as being added to others such as milk.

Pregnant women do not generally have tests to check their vitamin D levels. But many are asking if they should, or whether they should take supplements, said Dr. George Macones, chair of ACOG's committee on obstetric practice. "And for the most part, the answer is no."

Macones and his colleagues came to that conclusion after reviewing available evidence about the value of screening for low vitamin D levels in every woman who's pregnant - and finding a lack of data to prove a benefit to mother or baby.

Performing an additional blood test that has no benefit would be a waste of healthcare resources, said Macones. "If there isn't a reason to do it, you're just wasting money and time."

The only pregnant women who might benefit from a blood test for vitamin D deficiency - and it's not clear even for them -- are those who are at high risk for the problem in the first place due to certain diseases or other circumstances.

Last November, the Institute of Medicine said the highest amount of vitamin D women could safely take during pregnancy or breastfeeding was 4000 international units (IU) per day. For the average pregnant woman, the Institute recommends 600 IU of vitamin D daily. Most prenatal vitamins contain 400 IU, according to the ACOG report.

In an interview with Reuters Health, Macones explained that women can obtain extra amounts through sunlight and eating fish, as well as through milk and juices that have been specially fortified with vitamin D.

"I have no problem with women deciding to drink some extra fortified milk, or fortified juices," he said. And if a woman asked if she could take a supplement with modest amounts of vitamin D, "I would be okay with that," Macones added. "I just wouldn't routinely recommend it."

Although experts suspect that relatively high levels of vitamin D are safe in pregnancy, there could be some risks to supplements that researchers haven't uncovered yet, Macones said. "We think it's safe, but sometimes unexpected things turn up."

Still, a study last year by researchers in the United States suggested that pregnant women should dramatically increase their intake of vitamin D, in the form of supplements, to as much as 4000 IUs per day. The authors said there is little danger at that level. A review of previous studies published earlier this year concluded that many women have low blood levels of vitamin D early in pregnancy, but it's unclear whether a deficiency stunts fetal growth or causes other pregnancy-related complications.

To date, researchers have not published a randomized controlled study of the effects of vitamin D on pregnancy. That type of trial yields the most reliable results.

Given the lack of conclusive evidence, the ACOG committee did not recommend that pregnant women be screened routinely for vitamin D deficiency and take supplements. Its report appeared online June 20th in ACOG's monthly medical journal, Obstetrics & Gynecology.

Dr. Carol Wagner at the Medical University of South Carolina told Reuters Health that the committee's conclusions are "sound based on the information published," but she and her colleagues recently conducted a randomized controlled study of 350 pregnant women who received either 400, 2000, or 4000 IUs of vitamin D per day. The results, which may be published in a few weeks, showed that 4000 IUs was the "optimal dose" to help pregnant women produce the active, hormonal form of vitamin D, Wagner said.

But does that lower mom's or baby's risk for problems before or after delivery? The answer is clear yet.

For now, as Wagner said in an email, "According to the IOM and the Endocrine Society, up to 4000 IU per day is safe during pregnancy; any dose above that should be taken in consultation with the patient's physician."