Source: The Decline in Fertility: The Role of Marriage and Education — Penn Wharton Budget Model
As of 2019, about 41% of adult women age 25+ had at least a 4-year college degree.
Those with college degrees are less likely to have children. This correlation is similar to the finding that families with higher incomes are also less likely to have many children.
Economic success – which is seen over most of the world today – has led to families having fewer children.
This is one factor among many.