ABSTRACT
STUDY QUESTION: Do daughters of women with endometriosis exhibit an increased risk of endometriosis and impaired long-term reproductive prognosis when compared with daughters of women without endometriosis? SUMMARY ANSWER: Daughters of women with endometriosis have over a 2-fold higher risk of endometriosis but no difference in long-term reproductive prognosis compared with controls. WHAT IS KNOWN ALREADY: Several studies have found an increased prevalence of endometriosis in sisters and mothers of women with endometriosis, but none have examined the long-term reproductive prognosis in daughters of these patients. STUDY DESIGN, SIZE, DURATION: A controlled historical cohort study with a 33-year follow-up. PARTICIPANTS/MATERIALS, SETTING, METHODS: Among women 15-49 years old during the period 1977-1982, 24 691 were diagnosed with endometriosis during the study period. These women were age matched to 98 764 women without endometriosis. Daughters of these two groups were followed until 31 December 2009 for an endometriosis diagnosis and reproductive outcomes. Women were excluded from the study at death or if they emigrated. MAIN RESULTS AND THE ROLE OF CHANCE: Except for 4-6% of emigrated women, the follow-up rate of the study was almost 100%. Daughters of women with endometriosis (n = 12 389) had a 2.12-fold (95% confidence interval 1.89-2.37, P < 0.0001) increased risk of being diagnosed with endometriosis, compared with daughters of women without endometriosis (n = 52 371). Delivery rate, risk of spontaneous abortions and ectopic pregnancies were similar for the two cohorts, whereas induced abortions were slightly more frequent in the exposed cohort. LIMITATIONS, REASONS FOR CAUTION: The most important limitation of the study was the lack of data concerning the attempt to become pregnant. Also, some women with endometriosis might never be diagnosed with the condition. This applies to both the control mothers and the control daughters, but also the daughters of mothers with endometriosis. Other limitations are lack of accounting for potential confounders and the lack of data on preterm birth. However, the influence of most confounding factors was expected to be minimal because of the close matching by age of controls. WIDER IMPLICATIONS OF THE FINDINGS: The external validity of the study is expected to be high owing to the unselected inclusion criteria. The encouraging finding was that despite the increased risk of being diagnosed with endometriosis, daughters of women with endometriosis have a reproductive prognosis comparable with that of daughters of women without endometriosis. STUDY FUNDING/COMPETING INTEREST(S): The Department of Gynaecology at Rigshospitalet University Hospital, Copenhagen, covered all expenses of the study. Ø.L. has, within the last 3 years, received honoraria for speeches in pharmacoepidemiological issues and has been expert witness in a legal US case in 2011-2012. None of the other authors have any conflicts of interest.
