Estimation of a lower bound for the cumulative incidence of failure of female surgical sterilisation in NSW: a population-based study.

Abstract

Female tubal sterilisation, often referred to as "tubal ligation" but more often performed these days using laparoscopically-applied metal clips, remains a popular form of contraception in women who have completed their families. A review of the literature on the incidence of failure of tubal sterilisation found many reports of case-series and small clinic-based studies, but only a few larger studies with good epidemiological designs, most recently the US CREST study conducted during the 1980s and early 1990s. The CREST study reported a conditional (life-table) cumulative incidence of failure of 0.55, 0.84, 1.18 and 1.85 per 100 women at 1, 2, 4 and 10 years of follow-up respectively. The study described here estimated a lower bound for the incidence of tubal sterilisation failure in NSW by probabilistically linking routinely-collected hospital admission records for women undergoing sterilisation surgery to hospital admission records for the same women which were indicative of subsequent conception or which represented censoring events such as hysterectomy or death in hospital. Data for the period July 1992 to June 2000 were used. Kaplan-Meier and proportional-hazards survival analyses were performed on the resulting linked data set. The conditional cumulative incidence per 100 women at 1, 2 4 and 8 years of follow-up was estimated to be 0.74 (95% CI 0.68-0.81), 1.05 (0.97-1.13), 1.33 (1.23-1.42) and 1.51 (1.39-1.62) respectively. Forty percent of failures ended in abortion and 14% presented as ectopic pregnancies. Age, private health insurance status and sterilisation in a smaller hospital were all found to be associated with lower rates of failure. Strong evidence of time-limited excess numbers of failures in women undergoing surgery in particular hospitals was also found. The study demonstrates the feasibility of using linked, routinely-collected health data to evaluate relatively rare, long-term outcomes such as sterilisation failure on a population-wide basis.