The management of an adnexal mass in pregnancy depends on the gestational age at which it is diagnosed and the likelihood that complications will develop. In early pregnancy, the corpus luteum is frequently observed using transvaginal ultrasound and appears as a simple cyst. The corpus luteum provides progesterone support of the pregnancy until the placenta assumes this role in the latter part of the first trimester. Although uncommon, corpus luteum cysts may enlarge and undergo hemorrhage or torsion and become symptomatic. If resection is required prior to 10 weeks' gestation, supplementation with progesterone should be given through the 10th week.
The management of asymptomatic adnexal masses identified in early pregnancy depends on the size and sonographic appearance of the mass. In general, masses that are smaller than 5 cm, cystic, and simple require no follow-up. Larger masses or those with complex features are usually followed with repeat ultrasound in the early second trimester. Those that persist may require surgical resection, particularly if they are 5 cm or larger or have features that are suspicious for malignancy, such as thick internal septations or papillary excrescences. Larger masses, even when benign, increase the risk for ovarian torsion, which can result in adnexal necrosis, peritonitis, and preterm labor. The risk for ovarian torsion appears to be greatest in the first half of pregnancy as the gravid uterus grows out of the pelvis. Elective removal in the early second trimester can prevent this complication. It should be emphasized, however, that the optimal management of persistent masses of intermediate size (5–10 cm) that are believed to be benign is unclear, and decisions should be made on an individual basis. If there is suspicion for ovarian cancer, preoperative consultation with a practitioner experienced in treating gynecologic malignancies is appropriate.
American College of Obstetricians and Gynecologists. Practice Bulletin No. 174: Evaluation and management of adnexal masses. Obstet Gynecol. 2016 Nov;128(5):e210–26.