Equipoise of recent estimated Down syndrome live births in Japan.

To support people with Down syndrome (DS), it is essential to know and predict the number of live births of children with this condition. In this study, we estimated DS live birth rates on the basis of maternal age distribution and numbers of births in the general population, the maternal-age specific chance for a live birth of a child with DS, and the prenatal diagnosis/termination rate. The total number of live births in Japan decreased to less than 1 million in 2016 and the percentage of women aged 35 years old or over giving birth has increased by sixfold. Prenatal genetic testing in Japan has gradually become more widespread, and 20% of all cases of DS were diagnosed prenatally in 2016. Meanwhile, the annual projected number of DS live births has remained steady at around 2,200 (22 per 10,000 births). In 2016, it was estimated that 70% of all DS babies were born to women of advanced maternal age (AMA). Given that Japan is facing a decreasing birth rate and an aging population, adoption of the practice of prenatal genetic testing for AMA has balanced the number of DS births over the last 7 years from 2010.