Naylor A F, Warburton D
Fertil Steril. 1979 Mar;31(3):282-6.
Evidence from more than 14,000 reproductive histories in the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke indicates that the risk of spontaneous abortion increases considerably with gravidity. Maternal age, memory errors, and sampling bias related to recurrence risk do not account for the trend. Clustering, or tendency for abortions to follow one another, occurs in histories which include live births.
美国国立神经疾病与中风研究所围产期协作项目中超过14000例生育史的证据表明，自然流产风险会随着妊娠次数显著增加。产妇年龄、记忆误差以及与复发风险相关的抽样偏差并不能解释这一趋势。在包含活产的生育史中会出现流产聚集现象，即流产倾向于相继发生。
