Babies born to women who used lithium therapy to treat bipolar disorder during their first-trimester of the pregnancy could be at an elevated risk of developing major congenital malformations such as heart defects, finds a study.

The findings, published in The Lancet Psychiatry, showed that nearly one and one-half times as many babies exposed to lithium during the first trimester experienced major malformations compared to the unexposed group (7.4 per cent compared with 4.3 per cent). In addition, risk for neonatal hospital readmission was nearly doubled in lithium-exposed babies compared to the unexposed group (27.5 per cent versus 14.3 per cent).

However, lithium exposure was not associated with pregnancy complications or other delivery outcomes, such as pre-eclampsia, preterm birth, gestational diabetes, or low birth weight, the researchers said. "Women should be informed on malformation risk in first-trimester exposed infants, but also about very high relapse risks for mental illness both during pregnancy and during the postpartum period," said Veerle Bergink, Professor at the Icahn School of Medicine at Mount Sinai in New York City, US.

The team examined the risk of congenital malformations such as heart defects and pregnancy complications in a meta-analysis of primary data from 727 lithium-exposed pregnancies compared to a control group of 21,397 pregnancies in mothers with a mood disorder who were not taking lithium. Lithium therapy is widely recommended as a first-line treatment for bipolar disorder, which affects approximately two per cent of the world's population. It also helps prevent severe depression and mania.

"Given the well-documented effectiveness of lithium in reducing relapse in the perinatal period, some important clinical considerations are either to continue lithium in a lower dose during the first trimester or to restart lithium after the first trimester or immediately postpartum," Bergink said.