On the estimation of mean infecundable period following childbirth.

Abstract

Assuming that the expiration of lactation is caused by 2 competing forces a model is presented to estimate with best possible precision the mean period of natural infecundability following childbirth. In general a lactating mother following childbirth is considered infecundable. Sometimes however menstruation may freshly recommence before the end of the period of lactation and place the mother at risk of reconception. Assuming that post partum amenorrhoea (PPA) expires sometime soon after the end of lactation what is the expected longevity of the lactation period? This mathematical model offers a solution to estimating both the mean length of PPA when lactation period continues after the end of the former. The model accomplishes this task by weighting the mean infecundable period with the respective probabilities that lactation will last longer that PPA or vice versa. A precise estimation lies somewhere between the 2 scenarios. Freunds 1961 bivariate exponential model is used to illustrate the methodology.