A study of seasonal and secular trends in incidence of stillbirths and spontaneous abortions in Sweden.

Abstract

Abstract. An investigation was made of secular and seasonal trends in two aspects of reproductive failure: stillbirth and spontaneous abortion. The study of stillbirths during 1965 to 1971 is based on official statistics for the whole of Sweden, representing a total of 3 371 stillbirths among 445 343 births. The date of last menstrual period (LMP) was estimated for the main material from data obtained from a smaller series of 181 stillborn infants in Malmö. Spontaneous abortion was studied in the population of Malmö during 1969 to 1971. The yearly number shows a decrease from 369 in 1969 to 330 in 1971. The trend towards performing legal termination of pregnancies at earlier gestation periods means that more terminations are being performed on patients who might subsequently have aborted spontaneously.After correcting for this the number of spontaneous abortions was constant: in 1969 389, in 1970 391, and in 1971 390. The total number of pregnancies in Malmö was 3 345, 3 511 and 3 360, respectively. Incidence of stillbirth and spontaneous abortion was determined, according to month of LPM.A decrease in stillbirth rate was observed after 1967, particularly in the high maternal age groups (over 35 years). A seasonal rhythm was noticed with a high stillbirth rate among pregnancies with maternal LMP around March and a low rate in women with their LMP during the summer. A high stillbirth rate is correlated with a low pregnancy rate. Spontaneous abortions show a different pattern‐with a high rate of spontaneous abortion among pregnancies in women with their LMP around June or at the end of the year. There is apparently no correlation between the seasonal changes in stillbirths and spontaneous abortions.