Temporal trends in incidence and outcome of hydatidiform mole: a retrospective cohort study

Reported incidence rates of hydatidiform mole (HM) show wide geographic and temporal variations, making reliable international comparisons difficult. The aim of the current study was to examine temporal trends in the incidence of HM and post-molar gestational trophoblastic neoplasia (GTN) in Stockholm County.

Data of all women with a diagnosis of HM in Stockholm County 1991-2010 was collected. The incidence of HM was assessed both in relation to number of births and viable conceptions (births and pregnancy terminations). The risk of post-molar GTN was analysed for all HM, as well as for the subtypes complete (CHM) and partial hydatidiform mole (PHM). Temporal trends were analysed by stratifying the study period into five-year intervals.

The overall incidence rate of HM was 2.08/1000 deliveries and 1.48/1000 viable conceptions. A significant temporal increase in the incidence rate of HM, as well as in the total number and proportion of PHM, was seen. Among 956 women with HM, 77 (8%) progressed into post-molar GTN. There was evidence of a slight, but non-significant increase in the risk of malignancy in the two last five-year periods under study.

We found evidence of a significant temporal increase in the incidence rate of HM, which could not fully be explained by an increase in maternal age over time. Changes in diagnostic methods probably contributed to the increased incidence rate of PHM. The risk of post-molar GTN remained constant over time.