Ectopic pregnancies following female sterilization. A matched case-control analysis.

The present study compared 15 ectopic pregnancies occurring after female sterilization (EPs) with 30 non-pregnant control patients who had also undergone female sterilization (NPCs) for a history of induced abortion, any pelvic surgery, abdominal surgery, or pelvic infection. EP cases and controls were individually matched for clinic, surgeon, surgical approach, tubal occlusion technique, and date of operation, as well as patients age and parity. The only significant difference was the greater proportion of EP patients, reporting a history of induced abortion (matched triplet odds ratio = 9.0, 95% confidence limits = 1.39, 58.26). Women with EPs were further compared with 78 women with post-sterilization intra-uterine pregnancies (unmatched). Results again show a significantly greater risk of conceiving an EP following previous induced abortion (odds ratio 5.8, 95% confidence limits = 1.78, 18.60). Women with previous abdominal surgery also ran a significantly higher risk of post-sterilization EP (odds ratio 10.0 95% confidence limits = 2.45, 40.83). Limitations of the data and clinical implications of the results are discussed.15 cases of ectopic pregnancy following sterilization and 30 matched nonpregnant, sterilized controls were compared for a history of induced abortion, adbominal surgery, and for several other characteristics. The 15 ectopic pregnancy cases constituted all ectopic pregnancies known to have occurred among the 23,640 wemen who were sterilized between 1973-79 at International Fertility Research Program (IFRP) study centers around the world and followed up for at least 6 months. The controls were selected from the same population. An attempt was made to match 2 controls to each case in regard to sterilization provider characteristics and acceptor characteristics. Provider characteristics included the specific clinic, the surgeon, the surgical approach, the tubal occlusion technique, and the data of sterilization; acceptor characteristics were age and number of live births. All matching requirements were met for 9 of the cases and all but 1 requirement were met for the remaining 6 cases. Matched triplet odds ratios were calculated, and 95% confidence intervals were computed. The only significant difference between the cases and controls was that a greater proportion of cases (40.0%), compared to controls (13.3%), reported a history of 1 or more induced abortions prior to sterilization. The odds ratio was 9.0, and the 95% confidence limits were 1.39 and 58.26. Most of the abortions occured before the last pregnancy prior to sterilization. 3 of the cases and 1 of the controls had more than 1 induced abortion prior to sterilization. 26.7% of the cases and only 13.3% of the controls reported abdominal surgery prior to sterilization; however, the difference between the 2 groups was not significant. No significant differences between cases and controls were observed in reference to race, residence, education, contraceptive use prior to sterilization, outcome of last pregnancy, pregnancy status at the time of sterilization, systemic disease histories, prior spontaneous abortions, prior child loss, or pre-existing pelvic infection at the time of sterilization. 14 of the ectopic pregnancy cases were further compared with 78 unmatched cases of intrauterine pregnancy following sterilization. The 78 cases were drawn from the same IFRP population. Again, the ectopic pregnancy cases had a higher proportion of prior induced abortions than the intrauterine pregnancy group. The odds ratio was 5.75, and the 95% confidence limits were 1.78 and 18.60. In addition, a significantly higher proportion of ectopic cases compared to the intrauterine pregnancy cases experienced abdominal surgery prior to sterilization. The clinical implications of the findings and the limitations and advantages of the study's design were discussed.