The aim of this study was to examine the incidence and characteristics of women who develop a second molar pregnancy after a previous episode of gestational trophoblastic disease.A retrospective analysis was carried out on completed registration forms from referring hospitals in the North of England to the Sheffield Trophoblastic Screening Service over a 13-year period. All cases of second molar pregnancy were identified. Details of histology, blood group, ethnic origin, age, and subsequent pregnancies were examined.Between 1 January 1985 and 31 December 1997, 5030 patients were registered for follow-up and 275 (5.5%) required treatment for persistent disease. Thirty-five women had a subsequent molar pregnancy, a total of 0.70% of all registrations. There was no significant difference in age at first registration between those who were registered for one molar event and those who developed a subsequent molar pregnancy. The risk of a second molar event was highest in the second year after the initial diagnosis and reduced thereafter. There was a trend toward an increased risk of second molar pregnancy in Indian/Pakistani women when compared to Caucasian women (relative risk 2.4) but this was not significant at conventional levels. There was a significantly increased incidence of blood group B in patients that developed a molar pregnancy when compared to the normal population (P0.05), but there was no difference in distribution of blood group between those registered for their first molar event and those with two or more events. Patients who presented with a partial mole tended to have a partial mole as the second event but patients who presented with a complete mole were at risk of a subsequent complete mole, partial mole, or choriocarcinoma. Six percent of patients required chemotherapy for the second molar event, indicating no increase in aggressiveness in second moles. Two patients had three molar events.In the United Kingdom the risk of second molar pregnancy is less than 1%. There is an increased risk of molar pregnancy in women with blood group B and a trend toward an increased risk of second molar pregnancy in Indian/Pakistani women. Only 6% of patients required chemotherapy for the second mole; a second molar pregnancy is not an indication for chemotherapy.
