[The age incidence of spontaneous abortion]

A series of studies on the age incidence of spontaneous abortion was conducted. The results of the studies is summarized as follows: A total of 16,179 deliveries accompanied by 1,537 cases of spontaneous abortion in 5 hospitals was investigated. The ratio (spontaneous abortion/deliveries) was 0.095 (1,537/16,179) in all age groups, 0.197 (15/76) in the under 20 years age group, 0.089 (215/2,422) in 20-24 years age group, 0.083 (705/8,478) in 25-29 years age group, 0.090 (404/4,496) in 30-34 years age group, 0.232 (149/641) in 35-39 years age group, 0.650 (39/60) in 40-44 years age group and 1.169 (7/6) in the over 45 years age group. The ratio in the under 20 years age group was higher than the ratio in 20-34 years age group (P less than 0.05). The ratio in the over 35 years age group was higher than the ratio in 20-24 years age group (P less than 0.001). This results indicated that spontaneous abortions depended on the maternal age. Deliveries in 20-34 years old occupied 95.2% of all 16,179 deliveries and the incidence of spontaneous abortions in 20-34 age group was stable. It is suggested, that the spontaneous abortion is natural selection in the mother's body and nature protects the older mother's body from deliveries and child-rearing.