A decade ago, teen births nearly matched those of women ages 35-39, and they were almost quadruple that of women over 40. In just ten years, teen births halved, predominately due to improvements in the accessibility of birth control and education. On a fantastic note, the decline of teen births has occurred in tandem with a radical fall in the teen abortion rate. (When the teen abortion rate rose in the 70s, it was actually accompanied by an increase in teen pregnancies.)
Millennials are the first generation in the century to experience this sort of fall in teen pregnancies. So of course, that means the total fertility rate will fall as millennials, who were born in the 80s and 90s, enter their 20s, 30s, and 40s. In the past decade, the average age of first-time mothers increased from 25.9 to 27.7 in large metropolitan ares, 24.3 to 25.8 in smaller ones, and 23.2 to 24.5 in rural ones. That the decline of the birth rate fell in tandem with an increase, not a stagnation, of the age of first births indicates that most women aren’t choosing to forgo motherhood altogether, but rather postpone it, presumably improving their children’s economic support and stability.