Almost a fifth of American women in their early 40s have not had a child. Barring something very unusual, they will never have any.
The rule of thumb for all societies is that 90% of people marry, and 90% of them have children. This yields an average of 87% of the people in most populations have children.
Immigrants to the U.S. reproduce at exactly that rate: 87%. But the native population is down to 80%. Were it not for immigration our population would be declining.