Why is it that when trying to conceive, doctors don't want you to take nsaids?

See below: Nsaids are nonsteroidal antiinflammatory analgesics. They are not recommended in pregnancy, particularly during trimester. They are linked to premature births & miscarriages. They may affect the fetal kidney functions & premature closure of ductus arteriosus (vessel connecting pulmonary artery to aorta for fetal oxygen exchange). Acetaminophen (tylenol) is regarded as a safer alternative.

NSAIDS: Interefere with prostaglandin production, which is necessary for ovulation. In animal studies from late 1980s-90s ovulation could be inhibited by high-dose nsaid.