Use of the selective serotonin-reuptake inhibitor (SSRI) type of antidepressants, such as Prozac or Zoloft, during late pregnancy seems to raise the risk of a serious problem called pulmonary hypertension of the newborn (PPHN), investigators report.

PPHN occurs when blood pressures within the lung get too high, causing poorly oxygenated blood to be pumped to the rest of the body, Dr. Christina D. Chambers and her associates explain. Up to 20 percent of infants affected by the disorder do not survive.

Previous work by Chambers’ group suggested that use of fluoxetine (Prozac) in late pregnancy may be a risk factor for transient newborn complications, including PPHN.

Their current study, reported in The New England Journal of Medicine, included 377 infants with possible PPHN and 836 comparison infants born in one of four metropolitan areas. The mothers were interviewed within 6 months of delivery regarding their use of antidepressants.

Use of SSRIs overall or during the first half of pregnancy was not associated with the risk of PPHN. By contrast, taking such drugs after 20 weeks into pregnancy did seem to raise the risk of PPHN.

Chambers’ group suggests that the SSRIs may raise the risk of PPHN by increasing levels of serotonin in the lungs. This chemical could then work to tighten the blood vessels, resulting in elevated pressures.

Nonetheless, “about 99 percent of women exposed to one of these medications late in pregnancy will deliver an infant unaffected by PPHN,” the researchers stress.

“Pending further studies to confirm these findings,” they conclude, “clinicians and their patients must consider both the benefits of SSRIs in the treatment of depression and the potential risk of PPHN relative to the risks and benefits of alternative treatments or nontreatment.”

Echoing these recommendations in a related editorial, Dr. James L. Mills, from the National Institute of Child Health and Human Development in Bethesda, Maryland, observes that the study is based on a small number of cases, and that a mother’s untreated depression can also adversely affect the fetus.

“There is a pressing need,” he writes, “for experts to compare SSRIs with other forms of treatment to determine which are the safest, the most effective, and the best tolerated by pregnant women.”

SOURCE: The New England Journal of Medicine, February 9, 2006.