Lithium Teratogenicity — MRCPsych Paper B MCQ

Correct answer: C — 0.05–0.1%

Explanation lettering: B = shown as A · D = shown as B · A = shown as C · E = shown as D · C = shown as E

The traditionally quoted absolute risk of Ebstein anomaly following first-trimester lithium exposure is approximately 0.05–0.1%, or about 1 in 1,000–2,000, compared with a background risk near 1 in 20,000. The association is less certain and substantially smaller than early reports suggested; more recent studies have not consistently demonstrated a specific increase in Ebstein anomaly. This figure must not be confused with broader outcomes: one large cohort reported right ventricular outflow tract obstruction defects in 0.60% and all cardiac malformations in 2.41% of lithium-exposed infants. Thus options B and D may resemble broader cardiac-defect estimates but are too high for the traditionally quoted Ebstein-specific risk. Options C and E are also substantial overestimates. Counselling should balance this small potential fetal risk against the maternal and perinatal risks of bipolar relapse.

Reference: Royal College of Psychiatrists. Lithium in pregnancy and breastfeeding, section 'Does Lithium cause any birth defects?'. https://www.rcpsych.ac.uk/mental-health/treatments-and-wellbeing/lithium-in-pregnancy-and-breastfeeding