Hydatidiform mole in Nottingham: a 12-year retrospective epidemiological and morphological study.

The results of a 12-year retrospective study on the epidemiology of hydatidiform mole (HM) in Nottingham are presented. We have reviewed the histology of our cases of HM, tried to minimize selection bias, and have used the most reliable data available. Using data from two different sources we have calculated the frequency of HM as 1 in 1400 deliveries. The frequency of HM in this study is one quarter of that reported in an excellent study from Japan. We suggest that, with accurate epidemiological studies, the difference in frequency of HM between 'high risk' and 'low risk' areas is less than previously accepted. The present study also shows a lower incidence of persistent trophoblastic disease than previously generally accepted. We confirm that partial HM is a distinct clinicopathological entity and that two forms are distinguishable histologically. The malignant potential of partial HM is uncertain, and we suggest that the clinical management of partial HM should be no different from that of complete HM until further studies dictate otherwise.