Seasonality bias in adverse pregnancy outcomes in Siberia.

Objective: To examine which months are unfavourable for conception in the region with the severe continental climate.

Design: Retrospective population based study.

Methods: Monthly data on incidence rate for gestose, maternal anaemia, pyelonephritis, threat to spontaneous abortion, stillbirth, perinatal death and infant death at age under one year were extracted from medical records of obstetric, delivery, and paediatric hospitals in Novosibirsk (1976-1980), Norilsk (Taimir peninsula), and Mirny (western Yakutia). Two latter towns were considered together as a northern setting. Edwards' method was applied to test seasonality.

Results: In Novosibirsk as well as in northern towns, the monthly distribution of time of conception for preterm births, maternal pyelonephritis, and infant deaths displays significant seasonal pattern with maximum in summer. Additionally in the North, stillbirths' conceptions also tended to be concentrated in June.

Conclusion: In Siberia, the polar day and summer months are an unfavourable time for conceiving in respect to obstetric complications and adverse pregnancy outcomes.