Secularization and low fertility: how declining church membership changes couples and their childbearing

The impact of religion on family formation pattern and fertility is widely assumed to be of modest relevance in contemporary Western contexts. We argue that religious affiliation continues to play a significant role in social processes, and that secularization remains a driver of demographic trends. We examine the relationship between secularization and fertility decline in Finland from an individual and a couple perspective, amid a broader trend of declining birth rates in Western countries. We show that secularization can exert a self-reinforcing negative effect on fertility through an interplay of declining church membership, changing couple dynamics, and childbearing of religiously mixed and homogeneous couples. Using data from the Finnish administrative registers covering the period from 1995 to 2019, we are able to identify religious affiliation, as indicated by church tax payment in the secularized context of Finland. The analysis unfolds in two parts: first, we perform a demographic examination of the fertility trends of the religiously affiliated and unaffiliated groups; and, second, we use a dyadic perspective to explore the relationships between religious affiliation, couple composition, and the probability of having a first child. We conclude that the accelerated decline in church membership has contributed to the recent fertility decline.