Use of contraceptives prior to and after conception and exposure to other fetal hazards.

In a large prospective study, set up to determine whether reproductive outcomes are affected by prior contraceptive use, 34,344 women were recruited at their first antenatal visit and followed until pregnancy termination. This paper summarizes the study methods and describes the demographic differences between subjects who used various contraceptives shortly before conception, and those who experienced contraceptive failures. Thirty percent of the women had used oral contraceptives (OCs) during the 5 months prior to conception and 2.4% had continued using them after their LMP. IUDs had been used by 5.8% of women before conception and 1.1% after. If these rates are also true for the whole population of the U.S., they indicate that approximately 70,000 babies are born each year following pill-failures and 30,000 following failures of IUD's. Exposure to other fetal hazards was common, with 48% of pregnant women drinking alcohol, 28% smoking, and 15% receiving diagnostic X-rays. OC use was more common among smokers and drinkers, and OC failures were significantly associated with the use of anti-epileptics, aspirin, and with exposure to radiation.