Yudkin P L, Wood L, Redman C W
Lancet. 1987 May 23;1(8543):1192-4. doi: 10.1016/s0140-6736(87)92154-4.
In 40,635 deliveries in 1978-85, unexplained stillbirths were an important component (nearly a quarter) of all perinatal deaths. The rate of unexplained stillbirth (unexplained stillbirths divided by total births) was highest among preterm deliveries, fell to a minimum at 39-40 weeks' gestation, then rose at 41-42 weeks. Rate is generally accepted as measuring risk, but since it is the population of undelivered, not delivered, infants that is at risk of intrauterine death, stillbirth risk would be better measured as the number of impending stillbirths divided by the total number of undelivered fetuses. With this measure the risk of unexplained stillbirth was least in preterm pregnancies, rising fourfold after 39 weeks to a maximum at 41 weeks. At this time, it was also four times higher than at 33 weeks, in contrast to the rate, which was nineteen times lower.
在1978年至1985年期间的40635例分娩中，不明原因死产是所有围产期死亡的一个重要组成部分（近四分之一）。不明原因死产率（不明原因死产数除以总出生数）在早产中最高，在妊娠39 - 40周时降至最低，然后在41 - 42周时上升。通常认为比率用于衡量风险，但由于处于宫内死亡风险的是未分娩婴儿群体，而非已分娩婴儿，因此，死产风险用即将发生的死产数除以未分娩胎儿总数来衡量会更好。采用这种衡量方法，不明原因死产风险在早产妊娠中最低，在39周后上升四倍，在41周时达到最高。此时，该风险也是33周时的四倍，而比率则低19倍。
