Indomethacin as a tocolytic is contraindicated after 32 weeks because of risk of:

• A. Hyperglycemia
• B. Premature closure of the fetal ductus arteriosus with oligohydramnios due to impaired renal function
• C. Neural tube defects
• D. Hepatic toxicity

Answer: (B)

Prostaglandins keep the fetal ductus arteriosus open and also support fetal kidney blood flow and urine production. Indomethacin blocks prostaglandin synthesis, so it can cause the ductus arteriosus to constrict and close prematurely. After about 32 weeks, closing the ductus arteriosus can lead to adverse fetal circulation changes and markedly reduce fetal urine output, resulting in oligohydramnios. This combination poses risks to the fetus, making indomethacin tocolysis contraindicated late in pregnancy. While NSAIDs can have other toxicities, the key late-pregnancy concern is premature ductus arteriosus closure with oligohydramnios due to reduced renal perfusion.