Prolonging the period between marriage and the first birth reduces the effective age of childbearing in a woman and thus fewer children during her life. This paper aimed to study the interval between the beginning of the marriage till the conception of the first birth in terms of the length of this interval, childbearing probabilities, and the determinants that had a significant effect, for two groups of women, the first is for women who got married in the period that was characterized by a high total fertility rate. The second included the women who married during periods that were characterized by an acceptable downward trend in fertility rates. The life table, Cox Proportional Hazard Model, and the Egypt Demographic and Health Survey for the year 2014 were used. The results showed a decrease in this interval in the first group, as compared to the second group. The differences between the two groups appeared slight in terms of the childbearing probabilities. There was no difference between the two groups in terms of the variables with a significant effect during that interval. According to Cox's analysis, the woman's education level, age at her first cohabitation, and the previous use of family planning methods are the only significant variables. It is necessary to raise and spread awareness about the married couples' need of getting reassured about the continuation of their marriages before deciding to have a child. This aims to reduce the effective age of a woman's ability to bear more children.