Cohort Analysis of Pregnancy Attempts

The number of pregnancy attempts that do not result in live birth is estimated for the cohorts born between 1953 and 1988 (sampled every five years) based on data for age-specific fertility rates from the Vital Statistics of Japan and on a theoretical model of the probability of infertility and spontaneous abortions derived from the literature on medicine and demography studies. I obtain an age profile to use for estimating the probability of pregnancy attempts by women in each cohort. For women born in the 1950s, the probability of a pregnancy attempt was high in their 20s, at 20 %, and rapidly decreased in their 30s. For women born in the 1960s, the rate was 10–15 % in their 20s and rapidly decreased in their 30s. The cohort total fertility rate thus started to decline in the 1960s cohort, due to declines in marriage and a delayed social life-cycle. For women born after the 1970s, this trend has continued. Reproduction is now mainly conducted by women in their 30s. Despite the considerable increase in the number of pregnancy attempt by women older than 35 years in today’s Japan, the number of childbirths has not increased, because of the increasing possibility of infertility and spontaneous abortions stemming from biological causes.