CHICAGO – Longer oral contraceptive use plus parity were protective against the development of endometriosis in a retrospective cohort study of young women in the Australian Longitudinal Study on Women’s Health.
Researchers analyzed data at four time points over a 10-year-period from a subset of 9,427 women aged 18-23 years at the time of entry in the ALSWH. The study is prospectively following 40,000 women over a 20-year period to better estimate the association between oral contraceptive (OCP) use and risk of endometriosis.
A total of 514 new endometriosis cases occurred over the 10 years, with an incidence rate of 670 per 100,000 person-years of risk, Dr. Frank Tu and his associates reported in a poster at the annual meeting of the International Pelvic Pain Society.
Dr. Frank F. Tu
Univariate analysis revealed that immediate prior OCP use was a risk factor for endometriosis. In bivariate analysis, however, OCP use was a risk factor for endometriosis in nulliparous women but not in parous women.
The researchers then conducted a multivariate Cox regression analysis that adjusted for such confounders as body mass index (BMI), parity, geographical location, OCP use for other reasons, urinary pain, marital status, SF-36 (Short-Form–36) pain score, dysmenorrhea, total years of OCP use, and its interaction with parity.
In this analysis, nulliparous women with prior exposure to OCPs had a dose-dependent increased risk of developing endometriosis; however, prior exposure to OCPs was protective among parous women, reported Dr. Tu of the NorthShore University Health System in Chicago.
Compared with nulliparous women who never used OCPs, the risk for a subsequent diagnosis of endometriosis was 1.8 times higher in nulliparous women who had used OCPs for less than 5 years, and 2.3 times higher in those with at least 5 years of OCP use.
In contrast, parous women with 5 years or more of OCP exposure had a significant 59% reduced risk of endometriosis, compared with those who never used OCPs. The risk of endometriosis was reduced 55% in parous women with less than 5 years of OCP, but this did not reach statistical significance.
"While our study revealed that longer OCP use plus parity were protective against endometriosis, rigorous mechanistic studies are needed to validate if use of exogenous sex hormones is a risk factor for the development of endometriosis and pelvic pain conditions among nulliparous women," the authors concluded.
At midstudy, endometriosis patients were significantly more likely than controls to report having heavy menstrual periods "sometimes or often" (46% vs. 25%), having constipation (19% vs. 13%), painful urination (17% vs. 8%), severe period pain (64% vs. 38%), low back pain (48% vs. 37%), and depression (4% vs. 2%).
Roughly two-thirds of cases and controls had an acceptable BMI of 18.5-25 kg/m2 (68% vs. 69%), one-third had some post–high school education (29% vs. 30%), and few were married (10% vs. 9%).
Dr. Tu disclosed no conflicts of interest.