Age at first birth and the pacing of subsequent birth intervals: A cohort analysis

This study elaborates on previous research which has explored the relationship between age at first birth and subsequent fertility. Using life tables and proportional hazard models, data from the 1973 and 1988 cycles of the National Survey of Family Growth for two cohorts--1930-34 (the Baby Boom period) and 1945-49 (post Baby Boom period)--are analyzed. Consistent with previous research, findings suggest that the relationship between age at first birth (under 25 vs. 25 and older) and the pace of subsequent births has weakened for the second birth interval because younger women at first birth have experienced longer intervals than younger women in the past, and older women at first birth have experienced about the same birth interval lengths. However, for the third interval, the relationship between age at first birth and the pace of the third birth interval has not weakened and may indeed be stronger; both younger and older women in the recent cohort experienced longer intervals than women in the earlier cohort. The present study adds to previous research in two crucial respects. First, it incorporates into data analysis measures of contraceptive use, mother's labor force participation, and marital disruption during the second and third birth intervals. Second, it examines in detail the effects of contraceptive sterilization on the relationship between age at first birth and subsequent birth pacing. Results of these analyses suggest that further research along these lines will add substantially to understanding changes in the relationship between age at first birth and the pacing of subsequent births since the Baby Boom period.