A 32-year-old woman at 8 weeks of gestation with bipolar disorder is on lithium carbonate 900 mg daily (serum level 0.8 mEq/L). She is euthymic and wishes to continue the pregnancy. What is the most appropriate next step in management?

Explanation

## Lithium Use in Pregnancy: Risk–Benefit Analysis ### Teratogenic Risk of Lithium **Key Point:** Lithium is a Category D drug in pregnancy. First-trimester exposure is associated with a 2–3-fold increased risk of congenital heart defects, particularly **Ebstein's anomaly** (tricuspid valve abnormality). The risk is highest with exposure in weeks 2–8 of gestation (organogenesis). **High-Yield:** Despite teratogenic risk, lithium is NOT absolutely contraindicated in pregnancy. The decision to continue must weigh maternal psychiatric stability (risk of relapse, suicide, infanticide) against fetal risk. Many women benefit from continuation with close monitoring. ### Teratogenic Profile of Lithium | Trimester | Risk | Clinical Significance | |---|---|---| | **First (weeks 2–8)** | Ebstein's anomaly, other cardiac defects | Absolute risk ~1:1000 (vs. 1:20,000 in general population) | | **Second & Third** | Polyhydramnios, nephrogenic diabetes insipidus, goiter, hypothyroidism | Risk of maternal toxicity increases due to changing renal clearance | | **Neonatal** | Lithium toxicity, poor feeding, hypotonia, cardiac arrhythmias | Serum levels must be monitored postpartum | ### Recommended Management Strategy **If continuing lithium:** 1. **Informed consent and counselling** — discuss 2–3-fold increased cardiac defect risk vs. psychiatric relapse risk. 2. **Dose adjustment** — reduce dose by 25–50% in first trimester to minimize fetal exposure while maintaining maternal stability. Lithium clearance increases ~20–30% in pregnancy. 3. **Serum level monitoring** — check levels every 2–4 weeks (vs. every 3 months in non-pregnant patients). Target level: 0.4–0.6 mEq/L (lower than usual 0.6–1.2 mEq/L). 4. **Fetal echocardiography** — arrange at 18–20 weeks to screen for Ebstein's anomaly and other cardiac defects. 5. **Thyroid and renal function** — monitor maternal TSH and serum creatinine; assess for polyhydramnios on ultrasound. 6. **Postpartum planning** — anticipate dose increase after delivery (renal clearance normalizes); neonatal screening for lithium toxicity. **Alternative if stopping lithium:** - Valproate is **NOT safer** — it is Category X (contraindicated) due to high teratogenic risk (neural tube defects, developmental delay). - Lamotrigine is safer than valproate but less effective for bipolar disorder. - Atypical antipsychotics (e.g., quetiapine, aripiprazole) are Category C and may be used as adjuncts. **Clinical Pearl:** The absolute risk of Ebstein's anomaly with lithium is ~1 in 1000 (vs. 1 in 20,000 baseline). Many women with severe bipolar disorder choose to continue lithium because the risk of untreated maternal psychiatric illness (suicide, infanticide, poor prenatal care) often exceeds the fetal teratogenic risk. **Mnemonic: LITHIUM in pregnancy — Lower dose, Inform consent, Therapeutic monitoring, Hydrops/cardiac screening, Inform neonatology, Ultrasound (fetal echo), Monitor postpartum** [cite:KD Tripathi 8e Ch 12] [cite:Harrison 21e Ch 297]