Unsuspected pregnancy loss in healthy women.

A sensitive and specific radioimmunoassay was used to determine human chorionic gonadotropin (hCG) in serum samples obtained from 91 normal healthy women during 226 ovulatory cycles in which contraception was not being practised. Known conceptions occurred in 85 of these cycles; 74 ended in the births of live normal babies and the remaining 11 aborted spontaneously. Vaginal bleeding occurred at the expected time on the remaining 141 occasions and was accepted as normal menstruation by the patients; but concentrations of hCG consistent with pregnancy were detected in the serum of 7 individuals. Expressed as a proportion of conceptions, about 8% of human pregnancies are lost at such an early stage of development that the patients are unaware that conception has occurred.