MODELS RELATING THE TIMING OF INTERCOURSE TO THE PROBABILITY OF CONCEPTION AND THE SEX OF THE BABY

The probability that conception will result from intercourse on partic ular days of the menstrual cycle is of biological, demographic, and pe rsonal interest to many. We describe an existing model for conception as related to the timing of intercourse, and develop a method for fitt ing it by means of the expectation-maximization (EM) algorithm, using widely available software (GLIM). We then generalize the model to allo w for effects on its parameters due to reproductively toxic exposures. A further extension allows one to address the question of whether the pattern of intercourse in a conception cycle has an influence on the sex of the resulting baby. We illustrate the methods by application to data from a prospective study of couples trying to begin a pregnancy.