Lithium
Used for bipolar disorder. Early case reports (1970s Register of Lithium Babies) suggested a high rate of Ebstein anomaly (tricuspid valve defect), leading to decades of avoidance. More recent large cohort studies have substantially revised this estimate downward: the absolute risk of Ebstein anomaly is approximately 1 in 1,000 to 1 in 2,000 (versus 1 in 20,000 background) — a relative increase but low absolute risk. Fetal echocardiography at 18–22 weeks is recommended. Risk-benefit analysis is essential given that untreated bipolar disorder in pregnancy carries severe risks. Requires careful serum level monitoring as volume of distribution changes throughout pregnancy.
