Women undergoing infertility treatment are advised to avoid NSAIDs in preovulatory period because
Prostaglandin stimulates smooth muscle contraction in ovary, contributing to ovulation.  prostaglandin synthetase inhibitors if taken in pre ovulatory period can cause luteinized unruptured follicle syndrome (LUFS).
Prostaglandins contribute to ovulation
NSAIDs inhibit LH surge
NSAIDs cause premature rupture of follicle
NSAIDs like aspirin cause endometrial shedding.