Stillbirths in south-western Siberia during 1963-1991

Vladimir N. Melnikov, Siberian Independent Institute

To assess linear trend and seasonal pattern in stillbirth rate in Siberia a total of 1,220,932 live births and 9631 stillbirths for the period 1963–1991 in Novosibirsk region were examined using the maximum likelihood estimation based on Poisson distribution. Over the entire period, the mean monthly stillbirth rates were 10.9 and 8.8/1000 live births for urban male and female fetuses (p<0.001) declining during the time span, and 4.8 and 3.8 for rural males and females (p<0.1). During the 1963–1976 subperiod, the setting- and sex-specific seasonal variations were established. The amplitudes were higher for rural than for urban population and for females compared with males. Female fetuses exhibited a bimodal pattern while males showed a one-harmonic wave. The sex difference is suggested to be due to the differential sensitivity of fetuses to the sharp changes in ambient temperature in spring and autumn.