The average age of married mothers at the birth of their first child increased dramatically between the early 1960s and the first decade of the 21st century. This graph maps the drop in numbers of live first births to those under 25 years old, and the steady increase in the numbers of first births to women 25 years and over.

Particularly notable is the rapid increase in numbers of first births to married mothers 30–34 years from the mid-1980s and the gradual rise in the number of first births for women 35–39 years. In the early 21st century the number of first births to women 35–39 years was greater than the number of first births to women 20–24 years. At the same time, first births to those under 20 were fewer than the number of first births to women 40–44 years.