Epidemiology of endometriosis in women attending family planning clinics

Abstract

Objective: To describe the epidemiology of endometriosis in women attending family planning clinics with special reference to contraceptive methods.

Design: Non-randomised cohort study with follow up of subjects for up to 23 years. Disease was measured by first hospital admission rates since endometriosis can be diagnosed with accuracy only at laparotomy or laparoscopy.

Setting: 17 family planning centres in England and Scotland.

Subjects: 17,032 married white women aged 25-39 years at entry during 1968-74 who were taking oral contraceptives or using an intrauterine device or diaphragm. About 99% of the women approached agreed to participate and annual loss to follow up was about 0.3%.

Main outcome measures: Diagnosis of endometriosis, age, parity, and history of contraceptive use.

Results: Endometriosis was significantly related to age, peaking at ages 40-44 (chi 2 for heterogeneity = 30.9, p < 0.001). Endometriosis was not linked to duration of taking oral contraceptives. Nevertheless, the risk of endometriosis was low in women currently taking oral contraceptives (relative risk 0.4; 95% confidence interval 0.2 to 0.7), but higher in women who had formerly taken them (1.8; 1.0 to 3.1 in women who had stopped 25-48 months previously) compared with women who had never taken the pill. A similar pattern was seen for use of intrauterine devices (relative risk 0.4 (0.2 to 0.7) in current users and 1.4 (0.4 to 3.2) in users 49-72 months previously compared with never users). No association was found between endometriosis and use of the diaphragm.

Conclusions: Oral contraceptives seem to temporarily suppress endometriosis. Endometriosis may be diagnosed late in women using intrauterine devices as pain and bleeding occur with both.

PIP: Between 1968-1990, the Oxford Family Planning Association followed 313 women attending 17 family planning centers in England and Scotland who had been diagnoses with endometriosis as confirmed by laparoscopy and laparotomy to examine the epidemiology of endometriosis and its relation with contraceptive use. Only 4 women were infertile. Endometriosis rates rose significantly between the 25-29 year age group and the 40-44 year age group (0.13 vs. 0.81; p .001), so that the relative risk (RR) at 40-44 years was 6.1. Diaphragm use and endometriosis were not associated. Endometriosis was less likely to occur during pregnancy (RR = 0.05) and 4 years after pregnancy (RR = 0.4-0.6) than at most other times, but this was not significant. Current or recent (=or 12 months) use of oral contraceptives (OCs) appeared to protect against endometriosis (RR = 0.4). Yet, the risk of developing endometriosis was greater at least 1 year after stopping OC use (RR = 1.4-1.8). The researchers believed, however, that OCs only temporarily concealed the symptoms of endometriosis. Like OC use, current and recent IUD users and women who had last used an IUD 25-48 months earlier had a low risk of developing endometriosis (RR = 0.4 an 0.5, respectively). The RR increased for those who had last used an IUD at least 49 months prior to developing endometriosis (1.4). The researchers surmised that, since pain and bleeding are common clinical features of IUD use a endometriosis, providers removed the IUD rather than perform a laparoscopy or laparotomy to detect endometriosis, thereby accounting for the apparent protective effect. Further, providers probably diagnosed endometriosis later in IUD users because of the shared clinical features.