Seasonal changes in the frequency of fetal damages and fertility

Seasonality in twin birth rates, Denmark, 1936-84

A study was made of seasonality in twin birth rate in Denmark between 1977 and 1984. We studied all twin births (N = 45,550) in all deliveries (N = 3,679,932) during that period. Statistical analysis using a simple harmonic sinusoidal model provided no evidence for seasonality. However, sequential polynomial analysis disclosed a significant fit to a fifth order polynomial curve with peaks in twin birth rates in May-June and December, along with troughs in February and September. A falling trend in twinning rate broke off in Denmark around 1970, and from 1970 to 1984 an increasing trend was found. The results are discussed in terms of possible environmental influences on twinning.

Some epidemiological data on spontaneous abortion in Hungary, 1971-80

A population based survey of women who had spontaneous abortion in Hungary between 1971 and 1980 has been evaluated. Individual data sheets completed by specialists in obstetrical institutions were used. The ratio of spontaneous abortions was 13.1% during the whole period studied but declined during the decade. The maximum occurrence was in the fifth to eighth week of gestation, when more than 40% of all spontaneous abortions occurred. Thereafter spontaneous abortion ratios decreased gradually with duration of pregnancy. The distribution of spontaneous abortions by calendar month shows characteristic seasonal changes, the minimum values being found from April to July whereas the maximum values were from October to February. The spontaneous abortion ratios increased significantly with the age of mother, over age 40 it approached 50%. They also increased with the pregnancy order, a minimum figure being registered at the first pregnancy of women in their 20s. The risk for women with a history of spontaneous abortion was 33%.