Risk factors for ectopic pregnancy: a multi-center case-control study.

BACKGROUND: Ectopic pregnancy (EP) is the leading cause of maternal death during the first trimester of pregnancy. A better understanding of EP risk can help prevent its occurrence. We carried out a multi-center, large-sample, case-control study to evaluate the risk factors for EP in Shanghai, China.

METHODS: Women who were diagnosed with EP (n = 2411) and women with intrauterine pregnancies (n = 2416) were recruited from five hospitals in Shanghai, China. Information regarding the sociodemographic characteristics; reproductive, gynecological and surgical history; and previous and current use of contraceptives was collected from all participants. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated and adjusted for potential confounding factors via multivariate logistic regression analysis.

RESULTS: The study revealed that the risk of EP was associated with the traditional risk factors including previous EP (Adjusted odds ratio [AOR] = 2.72, 95% CI: 1.83-4.05), previous Chlamydia trachomatis infection (Adjusted OR = 3.18, 95% CI: 2.64, 3.84), previous infertility (AOR = 2.18, 95% CI: 1.66-2.88), previous adnexal surgery (AOR = 2.09, 95% CI: 1.49-2.93), previous appendectomy (AOR = 1.64, 95% CI: 1.13-2.37), and previous use of intrauterine devices (IUDs) (AOR = 1.72, 95% CI: 1.39-2.13). Additionally, EP risk was increased following the failure of most contraceptives used in the current cycle including IUDs (AOR = 16.43, 95% CI: 10.42-25.89), oral contraceptive pills (AOR = 3.02, 95% CI: 1.16-7.86), levonorgestrel emergency contraception (AOR = 4.75, 95% CI: 3.79-5.96), and female sterilization (AOR = 4 .73, 95% CI: 1.04-21.52). Stratified analysis showed that in vitro fertilization and embryo transfer (IVF-ET) was the main risk factor for EP in women with tubal infertility (AOR = 8.99, 95% CI: 1.98-40.84), although IVF-ET showed no association with EP in women with non-tubal infertility (AOR = 2.52, 95% CI: 0.14-44.67).

CONCLUSION: In addition to the traditional risk factors, IVF-ET and current IUD use play dominant roles in the occurrence of EP. Attention should be given to women with tubal infertility who have undergone IVE-ET treatment.