Letrozole-Induced Ovarian Hyperstimulation Syndrome Resulting in Quadruplet Pregnancy in a Young Nulligravida: A Case Report

Letrozole, an aromatase inhibitor, is widely used for ovulation induction due to its favorable safety profile, lower estrogen levels, and reduced risk of ovarian hyperstimulation syndrome (OHSS) and multiple pregnancy compared to clomiphene citrate and gonadotropins.Despite this, excessive ovarian response and high-order multiple gestation may rarely occur.We report a case of a 23-year-old nulligravida with primary infertility who underwent ovulation induction with letrozole.During her second cycle, she developed mild to moderate OHSS and subsequently conceived a quadruplet intrauterine pregnancy.One gestational sac underwent spontaneous demise, followed by selective fetal reduction from triplets to twins at 12 weeks of gestation.The antenatal period was uneventful until spontaneous preterm labour at 30 weeks, resulting in the vaginal delivery of live preterm twins.This case highlights that although letrozole is considered a low-risk ovulation-induction agent, clinicians should remain vigilant for rare complications such as OHSS and high-order multiple pregnancies.Careful monitoring and thorough patient counselling are essential to ensure optimal maternal and fetal outcomes.