A quasi-experimental study of abortion rates following gestational age limit changes in Japan

The relationship between of legislative changes in abortion regulations on women's decision-making remains understudied. In 1991, Japan reduced the gestational limit for abortion from 24 to 22 weeks of pregnancy. Here, using national data on abortions, stillbirths and live births at ≥12 weeks from 1989 to 1994 (n = 7,364,783), we examined the association of the change with abortion incidence rate and cumulative incidence between 12 and 27 weeks using quasi-experimental interrupted time-series and regression discontinuity analyses. After the change, incidence rates increased at 20 weeks (incidence rate ratio (IRR) 1.28, 95% confidence interval (CI), 1.15-1.43) and 21 weeks (IRR 1.33, 95% CI, 1.18-1.50), while decreasing at 22 weeks (IRR 0.25, 95% CI, 0.21-0.30, P < 0.001) and 23 weeks (IRR 0.07, 95% CI, 0.06-0.10, P < 0.001), and no meaningful changes for ≤19 or ≥24 weeks. Cumulative incidence decreased only for women at 19-23 weeks. In conclusion, the legislative change shifted abortions to earlier gestational ages, and was associated with fewer abortions among women who had reached 19th week of pregnancy.