Fecundability and coital frequency.

Abstract The analysis previouslyreported (Population Studies, 23, 1969) of the risk of conceptionon different days of the menstrual cycleis extended so as to take someaccount of the agesof wives. The risks are estimated from data (basal body temperatures and occurrences of coitus) recorded by 241 married couples not using any contraceptives, to whom at least one child had previously been born. A mathematical formula relating natural fecundability to coital frequency is proposed and considered.