Morphological changes of endometriomas during pregnancy and after delivery detected using ultrasound

OBJECTIVE: To assess changes in morphology and size of endometriomas during pregnancy and after delivery. DESIGN: This was a prospective observational cohort study performed during 2013-2024 at a tertiary care center (Ultrasound Unit, Department of Obstetrics and Gynecology, Skane University Hospital, Malmo, Sweden). Women were offered repeated ultrasound examinations every month during pregnancy and thereafter at 3 and 12 months after delivery. Ultrasound examinations were performed either transvaginally or transabdominally depending on the gestational week and assessability of the ovaries. SUBJECTS: Pregnant women with an ovarian cyst suggestive of endometrioma based on subjective assessment were eligible and those with the pregnancy that continued beyond gestational age of 22 weeks were included. In total, 57 women were included. EXPOSURE: Pregnancy. MAIN OUTCOME MEASURE(S): Changes in morphology (cyst type, cyst content, and signs of decidualization) and size of the endometrioma and the largest solid component were assessed during follow-up ultrasound examinations. RESULT(S): During pregnancy, endometriomas changed in morphology in 42/57 women (74%; 95% confidence interval [CI], 60-84) and decreased in size in 42/57 women (74%; 95% CI, 60-84). Decidualization of endometrioma was observed in 33/57 women (58%; 95% CI, 44-71) and was detected first time at gestational age of 17 weeks (median, interquartile range, 15-22; range, 6-29). The size of endometriomas decreased although the size of solid components increased from gestational age of 22+0 weeks. Signs of decidualization disappeared after delivery. CONCLUSION(S): Three out of four endometriomas undergo morphological changes during pregnancy. Decidualized endometrioma may mimic borderline malignancy, however, changes regress after delivery. Knowing the natural behavior of endometriomas during pregnancy is crucial to reducing the risk of misclassification of endometriomas as malignant masses. Follow-up ultrasound examination after delivery helps to reassure the benign nature of the cyst.