Endometriotic ovarian cysts do not negatively affect the rate of spontaneous ovulation

Study question: Do endometriotic ovarian cyst influence the rate of spontaneous ovulation? Summary answer: Endometriotic cysts, independently from their volume, do not influence the rate of spontaneous ovulation in the affected ovary. What is known already: It has previously been suggested that endometriotic ovarian cysts may negatively affect spontaneous ovulation. Study design, size, duration: This prospective observational study was per- formed between September 2009 and December 2012 in an academic referral centre for the treatment of endometriosis. Participants/materials, setting, methods: Inclusion criteria were: monolateral endometriomas (diameter ≥ 20 mm); regularity of menstrual cycle (24-35 days); desire to conceive. Exclusion criteria were: hormonal therapies in the 3 months before the study; previous adnexal surgery. Patients underwent serial transvaginal ultrasound to determine the side of ovulation (for up to six cycles). Main results and the role of chance: Ovulation was monitored in 1026 cycles in 214 women (age, mean + SD, 34.4 + 5.0 years). 56.5% of the patients had left endo- metriomas and 43.5% had right endometriomas (p , 0.001). The mean (+ SD) diameter of the endometriomas was 4.8 cm (+ 1.5 cm); the volume of the endome- triomas was 41.1 cm3. Ovulation occurred in 551 cycles in the healthy ovary (53.7%; 95% C.I., 50.6%-56.8%) and in 475 cycles in the affected ovary (46.3%; 95% C.I.,43.2%-49.4%; p 1⁄4 0.122). This observation was confirmed in patients with diameter of the cyst ≥ 4 cm (n 1⁄4 148) and in those with diameter of the cyst ≥ 6 cm (n 1⁄4 41). 83 patients conceived (38.8%; 95% C.I., 32.2%-45.7%). Limitations, reason for caution: The major limitation of this study consists in the fact that histological diagnosis of endometriosis was not required for inclusion in the study; however, transvaginal ultrasound has been shown to be accurate in the diagnosis of endometriomas. Wider implications of the findings: Since ovarian endometriomas do not impair spontaneous ovulation, surgical excision of the cysts should not be routinely per- formed with the aim to improve spontaneous fertility. Study funding/competing interest(s): None. Trial registration number: None.