Application of discrete time risk model to identify factors impacting on time to pregnancy

Objective To investigate the rationality of discrete time risk (DTR) model in identifying factors influencing time to pregnancy (TTP).Methods A questionnaire survey on TTP was conducted among 346 women taking prenatal examination at a third-grade class A hospital and 3 second-grade class A hospitals selected with random cluster sampling in Nanchong city of Sichuan province between October 2013 and January 2014.Discrete time risk model was adopted to analyze TTP among the women.Results Among the women,the estimated cumulative pregnancy probability (CPP) within 1-3,4-6,and 7-12 months were 60.69%,84.97%,and 94.51% based on the established DTR model A (excluding risk variables for TTP).The DRR model B(including history of induced abortionX₁and exposed to smoking of husband during the period of intended pregnancyX₂as the two risk variables of TTP) was also established.Base on the estimations of the model B,the CPP within 1-3,4-6,and 7-12 months were 60.41%,84.46%,and 93.96% for the women exposed to X₁,61.86%,85.58%,and 94.61% for the women exposed to X₂,and 56.46%,81.20%,and 91.95% for the women exposed to both X₁ and X₂; while for the women exposed to neither X₁ nor X₂,the estimated CPP within 1-3,4-6,and 7-12 months were 56.46%,81.20%,and 91.95%,respectively.Conclusion DTR model is a reasonable statistical technique for analysis of data on TTP,with the ability to identify risk factors and estimate CPP values under different covariates at given time intervals.