Lithium has been used in the treatment of pregnant women with bipolar disorder for many decades but information on the effects of its exposure on perinatal variables is scarce.

To determine the effects of in-utero exposure to lithium on neonatal outcomes among infants born to women with treatment with lithium during pregnancy.

Prospective and observational study including all consecutive cases of pregnant women with bipolar disorder type I or II (N = 22) and maintenance treatment with lithium monotherapy (n=13) or polytherapy (n=9), attended at the PERINATAL PSYCHIATRY PROGRAM CLÍNIC-BARCELONA between 2005 and 2012. We evaluated sociodemographic data, lithium plasma concentrations in maternal blood and umbilical cord, obstetric and neonatal variables.

No statistically significant differences were found regarding sociodemographic data between both groups. Rates for umbilical cord:maternal plasma lithium levels were higher in women treated with polytherapy than in women who received lithium alone (1.08 vs. 1.05). Neonates exposed to polytherapy had a higher weight percentile at birth (p70 vs p50) and greater gestational age (39.72 vs. 38.28 weeks), than those exposed to lithium alone. Acute neonatal complications were more frequently observed in infants that were exposed to lithium monotherapy (33.3% vs. 38.50), being all complications transitory and not severe.

The infants exposed to lithium polytherapy presented a higher weight at birth compared to those who received lithium monotherapy. However, no statistically significant differences were found between treatment groups. Further research is needed to better clarify safety of lithium and its effect on neonatal outcomes.