Comparison in Incidence of Hydatidiform Mole in Okinawa Islands and Mainland Japan

In East Asia, the incidence of hydatidiform mole is reported to be higher in Taiwan, Philippines and Indonesia than in Japan. The purpose of this study was to determine the incidence of the disease in Okinawa prefecture which is located near Taiwan, and to verify whether it is higher than that in mainland Japan. We determined the number and the incidence rate (per 100,000 population and per 1,000 live births) of trophoblastic disease by reviewing the cases of the disease registered from 1986 to 1995 in Okinawa prefecture and compared these figures with those obtained in prefectures of the mainland. During the 10 years, a total of 417 cases of hydatidiform mole were registered in Okinawa prefecture. It was reported that, during the same 10 years, a total of 13,322 cases of hydatidiform mole were registered in 21 prefectures of the mainland. The incidence rate per 1,000 live births of mole was not higher in Okinawa than in the mainland (p=0.8061), though the incidence rate per 100,000 population of mole was significantly higher in the former than in the latter (p=0.0111). The incidence of hydatidiform mole during the 10 years declined gradually and was approximately 1.5 per 1,000 live births, namely 1 in 500 live births in the recent years. In conclusion, the incidence rate per 1,000 live births of hydatidiform mole in Okinawa prefecture was not high compared with that in mainland Japan. Environmental factors did not seem to have a more profound effect on occurrence of molar pregnancy than ethnical factors.