Pregnant women on antidepressants are more likely to give birth to children with persistent pulmonary hypertension, according to a study published by the British Medical Journal on Thursday.

Persistent pulmonary hypertension is an increase in blood pressure in the lungs and can lead to shortness of breath and difficulty breathing, and although rare, it is a severe disease with strong associations to heart failure.

Researchers at the Centre for Pharmacoepidemiology at Karolinska Institutet in Stockholm Sweden evaluated 1,618,255 births between the year 1996 to 2007 in Denmark, Finland, Iceland, Norway and Sweden.

According to researchers, approximately 11,000 of the mothers were taking anti-depressants in late pregnancy and roughly 17,000 were taking the drugs in early pregnancy. Researchers said that those who did fill out a prescription were generally older mothers who also smoked, and 54,184 mothers had previously undergone psychiatric diagnosis but were not taking medication at the time of pregnancy.

Researchers analyzed several drugs that had been taken by expectant mothers including fluoxetine, fluvoxamine, citalopram, paroxetine, sertraline, fluvoxamine and escitalopram. The study noted that fluvoxamine had rarely been used, and none of the children with persistent pulmonary hypertension were exposed to it.

Researchers found 33 babies born with persistent pulmonary hypertension in the 11,014 mothers who took anti-depressants in late pregnancy, and 32 babies born with the disease out of the 17,053 mothers who used anti-depressants in early pregnancy. The study also found that a total of 114 babies whose mothers had previously been diagnosed with a mental illness suffer the disease.

Factors that were taken into account by researchers include infant’s year of birth, gestational age at birth, birth weight and infant signs of persistent pulmonary hypertension, as well as maternal smoking, body mass index during early pregnancy and maternal diseases including epilepsy, malignancies, arthritis, bowel disease, lupus and pre-eclampsia.

Researchers concluded that while the risk of developing pulmonary persistent hypertension is low at about three cases per 1000 women, the risk more than doubles if anti-depressants are taken during late pregnancy.