A retrospective multicenter study of the natural history of fetal ovarian cysts

Aim: We investigated the natural history of fetal ovarian cysts to estimate the risk of torsion according to size. Methods: Cases were identified from 1/1/2000 until 1/1/2015. Data were collected pre- and postnatally on cyst size and sonographic features until an outcome of surgery, torsion, or resolution. Fisher's exact test for categorical data and logistic regression for continuous data were used to test the significance of size on torsion; P value < 0.05 was considered significant. Results: 37 patients with unilateral ovarian cysts were included. 12 (32%) resolved spontaneously prenatally, 14 (38%) resolved spontaneously postnatally, 5 (14%) underwent surgery postnatally and 6 (16%) cases underwent torsion. Rate of torsion increased with size from 0% (n = 0) in cysts ≤ 20 mm to 33% (n = 2) in cysts > 50 mm; however, the overall trend failed to reach statistical significance (P = 0.1). Cysts of 0–40 mm had a significantly higher rate of spontaneous resolution (90% vs. 44% in > 40 mm, P = 0.003), but the rate of torsion was not significantly different (10% in 0–40 mm vs. 25% in > 40 mm, P = 0.26). The median time to postnatal resolution was 10 (5–27) weeks in those treated conservatively. Conclusion: Cysts > 40 mm are significantly less likely to resolve spontaneously; however torsion showed no significant correlation with cyst size. No complications were observed in cysts < 20 mm. Level of Evidence: IV, case series with no comparison group.