Prior studies have shown surgical excision of endometriomas are associated with a decline in ovarian reserve as assessed by serum anti-Mullerian Hormone (AMH) levels. However, the natural history of serum AMH levels in the presence of untreated endometriomas are unknown. Purpose of this study is to determine whether the presence of endometriomas cause a faster decline in serum AMH levels than in healthy women over a six months period.

The study is a prospective cohort study. Women diagnosed with endometriomas by transvaginal or transabdominal ultrasound or MRI will be recruited from a tertiary care endometriosis clinic. Age matched healthy controls will be recruited from the staff of the same hospital. A priorly published historical group of women who underwent endometrioma excision will be a second comparator.

Inclusion Criteria:

• Reproductive age
• Endometrioma without indication for surgery or treatment with combined contraceptive, progestin or other hormonal intervention.

Exclusion Criteria:

• Menstrual cycle irregularity
• Polycystic ovarian syndrome
• Women who were pregnant or contemplating pregnancy in the next six months
• History of ovarian surgery
• Using medication which could affect ovarian function during six months before recruitment
• Indication for surgical excision

The decision to include a healthy control group was taken five months after starting recruitment of women with endometrioma. Only 12 women with endometriomas had been recruited until then and none of them had six month serum AMH level measured.

Since healthy controls were reluctant to undergo transvaginal ultrasound examination, antral follicle counts were not measured as another marker of ovarian reserve for healthy controls and some women in the endometrioma group.