Shifts in peak month of births and socio-economic factors: a study of divided and reunified Germany 1950-2022.

Objectives: The seasonality of conception and birth has intrigued scientists for over 200 years. Since the 1970s, peak birth months in the northern hemisphere have shifted from early spring to late summer, influenced by oral contraceptives and socio-economic factors. The division of Germany from the end of World War II until reunification in 1990 offers a unique opportunity to analyze these influences while both regions had equal access to contraception. This study aims to identify differences in fertility trends and peak birth months between West and East Germany before and after reunification, considering political, socio-economic factors, and contraceptive availability.

Methods: A population-based study analyzed overall fertility rates, monthly birth data, peak birth months, and average maternal ages from 1950 to 2022.

Results: Fertility patterns were similar in both regions until 1970, showing a sharp increase post-1955 followed by a decline around 1965, likely due to contraception. From 1970 to 1990, East German fertility increased while West Germany's remained lower. After reunification, East German fertility fell sharply but later rose to West German levels. The peak birth month shifted from March to August in West Germany by the mid-1980s, while East Germany experienced this change 20 years later, post-reunification.

Conclusions: The 20-year delay in East Germany's shift suggests that oral contraception's impact was influenced by other factors, particularly the age of women at childbirth. Increased control over fertility in the West allowed for more choice in conception timing, a trend adopted in the East after gaining similar autonomy.