BOSTON, June 27 (Reuters) - Newer antidepressant drugs may increase the risk of birth defects but the risk remains very remote, according to two new studies published on Thursday.
The drugs, known as selective serotonin reuptake inhibitors or SSRIs, may cause a very small increase in the number of heart defects, but even this is unclear, researchers report in this week's issue of the New England Journal of Medicine.
"Researchers, did, however, find associations between SSRI use and three specific birth defects: a defect of the brain, one type of abnormal skull development and a gastrointestinal abnormality," the U.S. Centers for Disease Control and Prevention said in a statement.
"CDC plans to continue to study the association to clarify whether a true risk exists," it added.
"Any increased risks of these malformations in association with the use of SSRIs are likely to be small in terms of absolute risks," Dr. Michael Greene of Massachusetts General Hospital wrote in a commentary.
About 10 percent of pregnant women suffer from depression, according to the March of Dimes. The CDC says every pregnancy has a 3 percent risk of a major birth defect, regardless of exposures.
Concern over SSRIs surfaced nearly two years ago when a survey of 527 fetuses whose mothers took GlaxoSmithKline's Paxil during their first three months of pregnancy found that 4.4 percent were born with major malformations, usually of the heart.
The rate was 2.2 percent among women taking other antidepressants.
The finding prompted a change in labeling and new studies.
In November, a committee of the American College of Obstetricians and Gynecologists recommended that such drugs be discontinued if possible when a patient becomes pregnant. Prozac, made by Eli Lilly and Co.; Lexapro, made by Forest Laboratories Inc. and Zoloft, made by Pfizer , are all SSRIs.
OVERBLOWN CONCERNS
The New England Journal studies suggest that such concerns may be overblown. One found small increases in some uncommon defects and the other found no links in most cases.
"It should be recognized that the specific defects implicated are rare and the absolute risks are small," wrote one team, led by Carol Louik of Boston University, which looked at the cases of 15,709 babies.
Her group found, for example, no overall increase in the risk of heart defects, an original cause for concern.
In the second study, a group led by Sura Alwan of the University of British Columbia in Vancouver assessed data from 13,714 births to conclude that when a link between the drugs and a problem was discovered, the number of cases was too small to be definitive.
For example, they found that the risk of a child being born without a brain was 2.4 times higher if the fetus was exposed to an SSRI during the first three months of development. But that number was based on only nine affected babies who had been exposed to a drug, out of the 214 born with the defect.
They said letting a mother suffer from depression during pregnancy or discontinue her medicine if she suffers from serious depression can be dangerous to both herself and the child.
