The familial risk of endometriosis.

Objective: To study the occurrence of endometriosis or adenomyosis in mothers and sisters of patients with endometriosis.

Methods: A total of 563 patients with endometriosis were interviewed about endometriosis or adenomyosis in their mothers or sisters. Five hundred and twenty-eight patients (94%) gave information about their relatives. Six patients were adopted and had no knowledge about their relatives. Among 522 patients were seven pairs of sisters, of which only one was included, giving a total of 515 cases. The control group consisted of 149 women without endometriosis documented at a recently diagnostic laparoscopy performed in connection with sterilization. The controls were likewise interviewed about their relatives, and none refused to give information. If a gynecological operation in a relative was reported, medical records were obtained (68%) or a description of the medical history was given by the proband.

Results: Endometriosis or adenomyosis was disclosed in 3.9% of mothers of cases and in 0.7% of mothers of controls, in 4.8% of sisters of cases and in 0.6% of sisters of controls. The relative risk of endometriosis in a first-degree relative (expressed as odds ratio), was 7.2 (95% confidence interval 2.1, 24.3). Severe manifestations of endometriosis were found more often among patients with a positive family history than among those without (26% versus 12%, p < 0.01).

Conclusion: The study demonstrates a seven fold increased risk of endometriosis in mothers and sisters of patients with endometriosis. It is assumed that daughters of patients with endometriosis have a similar risk of developing endometriosis.