Effects of cyclic spouse separation on conception times

Abstract

The lengthening of conceptive delays under conditions of natural fertility by cyclic spouse separation is investigated as a problem in renewal processes. Separations are “complete” if they reduce the conditional monthly probability of conception, or fecundability, to zero, and “incomplete” if they merely reduce it, from f to r say. Earlier work respecting cyclic separation by Menken (1979) is extended with formulas for the mean and variance of conceptive delays conditional on T, the ordinal month of the cycle of separation and nonseparation when the woman passes from anovulation into the fecundable state. A simple expression relating fecundabilities f and r and the conditional proportions P s ( T) and P s -( T) conceiving during separation and nonseparation is obtained.