About one in 100 babies born to mothers taking certain types of antidepressants may develop an uncommon respiratory condition, researchers say.

The antidepressants studied were selective serotonin reuptake inhibitors, or SSRIs, such as Prozac, Paxil and Zoloft.

Infants born to mothers who took SSRIs in the second half of pregnancy had six times the expected risk of persistent pulmonary hypertension, an uncommon lung condition that can lead to serious neurological abnormalities. Out of every 1,000 babies born, two could develop this condition, which can clear up on its own.

Women who are taking the antidepressants are advised to check with their doctor before stopping the medication. Sudden withdrawal can be more dangerous than the relatively low risk of the lung condition. Untreated depression during pregnancy can also be a problem. It's estimated that 10 per cent of pregnant women suffer from clinical depression.

Last year, both Health Canada and the U.S. Food and Drug Administration warned of reports of possible side-effects of SSRIs on the fetus. The regulatory warnings did not include recommendations on alternative therapies.

Christina Chambers of the University of California, San Diego and her colleagues estimated about 99 per cent of women who took the antidepressants late in pregnancy would deliver an infant unaffected by persistent pulmonary hypertension.

They interviewed 337 women whose infants had the condition, compared to 836 other mothers.

They asked both groups of women about their use of medication during pregnancy, six months after they gave birth.

No increased risk of lung problems from SSRI was found before the 20th week of pregnancy or from taking other antidepressants while expecting.

"There is a pressing need for experts to compare SSRIs with other forms of treatment to determine which are the safest, the most effective and best tolerated by pregnant women," said Dr. James Mills in a journal commentary.

Five of the study's seven authors reported receiving funding from drug companies.