Objective：To show that it is possible to capture pregnant women by identifying newborns and their mothers using JMDC database and examine a generalizability to Japan.

Methods：We identified a newborn who was born between 2016 and 2020 and his/her mother using health insurance association's registry owned by JMDC Inc. First, we identified a newborn whose relationship to the insured was “child” and who joined the health insurance association at birth month. And we linked a woman member aged 18 to 49 who belongs to the same family at the newborn's birth month to the newborn as a mother. We assessed a generalizability of these mothers and newborns obtained from this method by an age distribution of mother at birth month and proportion of newborn against women aged between 18 and 49 using Vital Statistics, National Census, and Population Estimates in Japan as index.

Results：We identified 194,036 mother-newborn pairs in JMDC database from 2016 to 2020. The mean mother's age at newborn's birth was 31.9. On the other hand, the number of births in Japan during the same period was 4,538,786, and the mean mothers' age was 31.5. Number of newborns per 1,000 women in JMDC database in 2020 was 19.0, and that in Japan was 37.0.

Conclusion：We concluded that our method of identifying pregnant women and newborns is useful for study of pregnant women and newborns.