This extract is from a 'full prescribing brochure'.
(Category B, which means that there is no known association with birth defects or other pregnancy-related complication and the drug is probably safe.)
Pregnancy- category B.
Reproductive studies has been performed in mice at doses up to 9 times the human oral dose, in rats up to 44 times the human oral dose, in rabbits at a dose of 10mg/day delivered locally within the uterus by an implanted device, in guinea pigs at approx one half the human oral doseand in Rhesys monkeys at doses approx the human dose, all based on body surface area, and have revealed little or no evidence of impaired fertility or harm to the fetus due to progesterone.
Rare cases of congenital anomalities including cleft palate, cleft lip, ventricular septal defect, patent ductus arteriosus, and congenital heart defects have been reported in the infants of woman using Prometrium for unapproved indications including the preventions of such outcomes. Studies in humans cannot rule out the possibility of harm. Therefore, Prometrium capsules should be used during pregnancy only if indicated.
I started taking prometrium as soon as I found out I was pregnant because I was bleeding. I was bleeding a lot during the first 14 weeks of my pregnancy, going every week to get an ultrasound to see if the baby was still alive. My son was born at full term, with an aortic valve stenosis. He had the first procedure at 17 days old and he will need a new valve as soon as they can do the surgery. He is 7 years old now.