Seasonal distribution of abortions.

At least one pregnancy in eight terminates in an abortion recognized as such and recalled by women when asked for a pregnancy history (McDonald, 1958; Warburton and Fraser, 1964). Some women have a greater tendency to abort than others (Warburton and Fraser, 1964) and a few abort repeatedly (Eastman and Hellman, 1961). Gross fetal malformation undoubtedly accounts for some spontaneous abortions, and recently chromosomal abnormalities, especially trisomy, have been demonstrated in a substantial proportion (Singh and Carr, 1967; Dhadial, Machin, and Tait, 1970). The association of fetal trisomy with advancing maternal age may partly explain the higher risk of abortion observed in older women (Warburton and Fraser, 1964). The epidemiology of spontaneous abortions needs to be understood if we are to attempt to prevent the loss of normal fetuses in desired pregnancies, and the relationship between fetal defect and abortion makes it especially important. One of the main reasons for our ignorance is the difficulty in distinguishing spontaneous from procured abortions which are often concealed. An association between febrile illnesses in the first 12 weeks of pregnancy and abortion was reported (McDonald, 1958) and was also found in another