The paper discusses problems of model specification in birth interval analysis. Using Bongaarts’s conceptual framework on the proximate determinants on fertility, the paper tests the hypothesis that all important variation in fertility is captured by differences in marriage, breastfeeding, contraception and induced abortion. The paper applies a discrete time hazard model to study the second birth interval using data from the Egyptian Demographic and Health Survey 2000 (EDHS), and the month by month information on contraceptive use, breastfeeding, and postpartum amenorrhea available in the EDHS calendar. The paper shows the importance of including both information on contraceptive use by types, breastfeeding, and postpartum amenorrhea period in birth intervals analysis