Estimation of Unintended Fertility in Japan

Miho Iwasawa, National Institute of Population and Social Security Research, Japan

This paper evaluates a model that estimates the number of conceptions during the course of one year by all Japanese women of reproductive age (20-44). Data have been obtained from the Japanese National Fertility Survey, conducted in June 1997 (on reproductive intentions and fertility control behaviors) and from the official statistics on births and induced abortions for the year following the survey. In the model, the process of reproduction involves four stages: (1) intercourse, (2) reproductive intention, (3) conception, and (4) gestation and parturition. With some assumptions about fecundability and contraception failure, unknown parameters are estimated and the number of unintended pregnancies and unintended births can be calculated by this model. The model was applied to the female population in 1997 and suggested that the amount of unintended births could be between thirty and fifty percent of all births in contemporary Japan.