**Core Concept**
Antenatal corticosteroids, such as betamethasone, are administered to pregnant women at risk of preterm birth to accelerate fetal lung maturation and reduce the incidence of respiratory distress syndrome. This therapy is typically given in conditions where preterm delivery is anticipated but not immediately necessary.

**Why the Correct Answer is Right**
Chorioamnionitis, an infection of the fetal membranes, is a contraindication for antenatal corticosteroid administration. The use of corticosteroids in this setting may mask the clinical presentation of infection, potentially leading to delayed diagnosis and treatment. Infection in the fetal membranes can progress rapidly, causing severe complications for both the mother and the fetus. Administering corticosteroids may compromise the ability to promptly diagnose and manage chorioamnionitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Prolonged rupture of membranes for more than 24 hours is a condition where antenatal corticosteroids may be given to reduce the risk of respiratory distress syndrome in the preterm fetus. However, the decision to administer corticosteroids should be individualized based on the specific clinical scenario.

**Option B:** Pregnancy-induced hypertension is a common indication for antenatal corticosteroids, as these medications can help reduce the risk of respiratory distress syndrome in preterm infants.

**Option C:** Diabetes mellitus in pregnancy may be associated with an increased risk of preterm birth, and antenatal corticosteroids can be administered to promote fetal lung maturity in this context.

**Clinical Pearl / High-Yield Fact**
Antenatal corticosteroids are most effective when administered before 32 weeks of gestation, as their effects on fetal lung maturation are most pronounced at this stage. However, their use should be individualized based on the specific clinical scenario and the presence of any contraindications.

**✓ Correct Answer: D. Chorioamnionitis**