Lithium is an effective mood stabilizer and is widely used as a first-line treatment for bipolar disorder in the perinatal period. Several guidelines have provided clinical advice on dosing strategy (dose reduction versus stop lithium) in the peripartum period to minimize the risk of neonatal complications. An association has been observed between high neonatal lithium concentrations (> 0.64 mEq/L) and lower 1-min Apgar scores, longer hospital stays, and central nervous system and neuromuscular complications.

To quantify the rate of lithium placental passage at delivery. To assess any association between plasma concentration of lithium at delivery and neonatal outcome.

In this retrospective observational cohort study, we included women treated with llithium at least in late pregnancy. Maternal (MB) and umbilical cord (UC) lithium blood level measurement were collected at delivery. Lithium serum concentrations were determined by means of an AVL 9180 electrolyte analyzer. The limit of quantification (LoQ) was 0.20 mEq/L and detection limit was 0.10 mEq/L. From the medical records, we extracted information on neonatal outcomes (preterm birth, birth weight, Apgar scores, pH-values, and admision to NICU) and complications categoriced by organ system: respiratory, circulatory, hematological, gastro-intestinal, metabolic, neurological, and immune system (infections).

Umbilical cord and maternal lithium blood levels were strongly correlated: mean (SD) range UC/MR ratio 1.15 (0.24). Umbilical cord lithium levels ranged between 0.20 to 1.42 mEq/L. We observed no associations between umbilical cord lithium blood levels at delivery and neonatal outcomes.

In our study, newborns tolerated well a wide range of lithemias, between 0.20 and 1.42 mEq/L.

Women who take lithium during pregnancy and continue after delivery may opt to breastfeed, formula feed, or mix these options.

To evaluate the neonatal lithium plasma concentrations and nursing infant outcomes based on these three feeding trajectories.

We followed 24 women with bipolar disorder on lithium monotherapy during late pregnancy and postpartum (8 per trajectory). Lithium serum concentrations were determined by an AVL 9180 electrolyte analyser with a 0.10 mEq/L detection limit and a 0.20 mEq/L limit of quantification (LoQ).

The mean ratio of lithium concentration in the umbilical cord to maternal serum being 1.12 (0.17). We used the Turnbull estimator for interval-censored data to estimate the probability that the LoQ was reached as a function of time. The median times to LoQ was 6–8, 7–8, and 53–60 days for formula, mixed, and breastfeeding, respectively. Generalised log-rank testing indicated that the median times to LoQ differed by feeding trajectory (p = 0.037). Multivariate analysis confirmed that the differences remained after adjusting for serum lithium concentrations at birth (formula, p = 0.015; mixed, p = 0.012). We did not found any acute observable growth or developmental delays in any of the neonates/infants.

Lithium did not accumulate in the infant under either exclusive or mixed-breastfeeding. Lithium concentrations declined in all trayectories. The time needed to reach the LoQ was much longer for those breastfeeding exclusively. Lithium transfer via breastmilk is much less than via the placenta. We did not found any acute observable growth or developmental delays in any infant during follow-up.

No significant relationships.