Clinical overview
Adnexal masses are found in approximately 1–4% of pregnancies, with the rate now higher because of routine first-trimester ultrasound. The clinical challenge is multifaceted: most are benign (functional cysts, corpus luteum, dermoid), a meaningful minority are persistent benign neoplasms requiring surgical consideration, and a small but important subset (~1–6% of masses persisting beyond 16 weeks) are malignant. The pregnant uterus distorts surgical access, complicates anaesthesia, and changes risk-benefit calculations for both observation and intervention. Add the time pressure of advancing gestation and the patient's understandable anxiety, and you have a high-stakes counselling and decision-making scenario.
The fundamental triage question is symptomatic or asymptomatic, simple or complex, persistent or resolving, and malignancy-suspicious or not. For symptomatic masses (the focus of this objective) the dominant concerns are acute torsion, haemorrhage into a cyst, rupture, infection of a tubo-ovarian collection adjacent to gravid uterus, and a degenerating endometrioma. Each trimester carries its own surgical and obstetric considerations.
A registrar must be able to (1) generate a trimester-aware differential, (2) safely investigate while protecting the pregnancy, (3) counsel on observation vs intervention, and (4) operate timing surgery — usually second trimester — to minimise risks to both mother and fetus.
Core knowledge
Differential by mass type
- Functional (corpus luteum) cyst. Persists until ~10–12 weeks, then regresses as placenta takes over progesterone production. Usually unilocular, thin-walled, <6 cm.
- Theca lutein cysts. Multilocular, often bilateral; associated with high β-hCG (GTD, multiple pregnancy, OHSS).
- Mature cystic teratoma (dermoid). Most common neoplastic mass in pregnancy. Pre-existing; presence of fat and calcifications on imaging.
- Serous cystadenoma. Usually unilocular, thin-walled.
- Mucinous cystadenoma. Multilocular, can become very large.
- Endometrioma. Pre-existing; may decidualise in pregnancy (can mimic malignancy on imaging).
- Hyperreactio luteinalis. Bilateral cysts from exaggerated response to hCG; commonly with GTD or twins.
- Pedunculated fibroid. Mimics adnexal mass; check origin from uterus.
- Heterotopic pregnancy — rare in spontaneous, ~1:100 in ART. Important not to miss; see Ectopic pregnancy management.
- Malignancy — germ cell tumours (most common malignant in pregnancy because of young patient age — dysgerminoma, immature teratoma), borderline ovarian tumours, epithelial cancers, sex cord–stromal tumours.
Trimester-specific considerations
First trimester:
- Most masses are functional and will resolve by 16 weeks.
- Surgery rarely indicated unless severe symptoms (suspected torsion or rupture).
- Anaesthetic risk to embryogenesis (organogenesis 4–10 weeks); avoid teratogenic drugs.
- Risk of miscarriage from any surgery ~5–10%.