[Risk factors of ectopic pregnancy. A case-control study at 7 maternity units in the Paris area]

A case-control study was conducted in seven maternity hospitals in the Paris area in 1988 to evaluate the role of several risk factors in ectopic pregnancy (EP). A total of 279 cases and 307 controls were compared for sociodemographic characteristics, cigarette smoking, sexual reproductive and surgical histories and for the conditions under which conception occurred. Many factors were found to be associated with an increased risk of EP: cigarette smoking related to the number smoked at the time of conception (Odds Radio (OR) 1.26 to 2.72), appendicectomy (OR 1.25, 95% CI = 1.02-1.56), prior tubal surgery (OR = 2.42, 95% CI = 1.37-4.22), prior use of intrauterine devices (OR = 1.34, 95% CI = 1.02-1.80), induced ovulation cycle (OR = 1.66, 95% CI = 1.01-2.74) and prior EP (OR = 3.90, 95% CI = 2.27-6.75). Chlamydia trachomatis seropositivity was associated with an increased risk of EP (OR = 1.50, 95% CI = 1.04-2.13), but clinically reported pelvic inflammatory disease was not. Maternal age, parity, previous induced abortion and previous spontaneous abortion were not associated with EP. Use of an intrauterine device, progestagen micro-pill or the combined oestrogen/progestagen pill at the time of conception were associated with a lower risk of intrauterine pregnancy than of EP. These findings confirm the importance of several of the previously reported risk factors for EP; STD's, previous EP and cigarette smoking. They also identify new risk factors: appendicectomy, induced ovulation cycle, and showed that the combined oestrogen/progestagen pill does not prevent ectopic pregnancy as effectively as it prevents intrauterine pregnancy.