Adnexal masses in pregnancy: how often are they malignant?

The primary objective was to investigate the occurrence rates of benign and malignant ovarian tumors associated with pregnancy among women identified in three large California databases between 1991 and 1999. The secondary objective was to determine maternal and perinatal outcomes among these pregnancies.

This is a population-based study of 4,846,505 obstetrical patients using California hospital discharge records from 1991-1999. The California vital statistics birth/patient discharge database was linked to the California Cancer Registry (CCR). Cases of maternal ovarian cancers and low malignant potential (LMP) tumors were separated into three periods based on the timing of diagnosis and pregnancy: prenatal, at delivery, and postpartum. International Classification of Diseases, Revision 9 (ICD-9) codes were used to identify both diagnostic and procedural factors occurring during hospitalizations. The CCR database was used to identify cancer outcomes such as stage, histology, treatments, and vital status.

9375 women had a hospital diagnosis of an ovarian mass associated with pregnancy. CCR database identified 87 ovarian cancers and 115 LMP tumors in the same cohort. The occurrence rates were 0.93% (87/9375) ovarian cancers per total number of ovarian masses diagnosed during pregnancy, and 0.0179 ovarian cancers per 1000 deliveries. The summary stages of the ovarian cancers and LMP tumors were (respectively): localized 65.5% and 81.7%, regional 6.9% and 7.8%, remote 23.0% and 4.4%, and unknown 4.6% and 6.1%. 34 of the 87 ovarian cancers were germ cell tumors (GCT). Malignant ovarian tumors increased the likelihood of maternal outcomes such as cesarean delivery, hysterectomy, blood transfusions, and prolonged hospitalization compared to noncancer pregnant controls, but did not adversely affect neonatal outcomes. Cause-specific maternal mortality of patients with follow-up was 4.7% (9/191) at a mean of 2.43 years after diagnosis.

Ovarian malignancies are rare during pregnancy. Most maternal malignant ovarian neoplasms are early stage and associated with favorable maternal and neonatal outcomes. The low maternal mortality rate is likely due to the predominance of GCTs among the ovarian cancers.