Seasonal Variations in Conception Rates and Delivery Patterns: Environmental Influences on Reproductive Behavior in a Temperate Climate

Anecdotal evidence suggested a significant variation in monthly delivery patterns at a Southwestern United States hospital that serves as the primary teaching hospital of an Ob/Gyn Residency Program. The objectives of the present study were to confirm the existence of seasonal variability and to determine if there might be a relationship between the deliveries observed and local weather patterns (external temperatures, day lengths … etc.) at the time of conception. Restrospective delivery data were collected over a ten year period from 1992-2001 and compared to the average monthly weather conditions from the National Weather Service. A cyclic pattern to delivery numbers (P < .02) was confirmed and correlated with the fewest conceptions taking place in July and August, the hottest months with the longest daylight hours. While data only suggest a correlation between temperature patterns and deliveries, they do confirm a cyclic pattern correlating with time of year which can be used in staffing of the labor and delivery unit.