The average age for U.S. mothers who had their first baby in 2008 was 25, a year older than the average first-time mother in 1990. Among all women who had a baby in 2008, the average age is 27, up from 26 in 1990. The prime child-bearing years remain 20-34 — three-quarters of mothers of newborns are in this age range. Birth rates peak among women in their late 20s.

Since 1990, birth rates have risen for all women ages 30 and older. Although in some cases the number of births is small, the rate increases have been sharpest for women in the oldest age groups — 47% for women ages 35-39 and 80% for women ages 40-44, for example.

This delay in age of motherhood is associated with delay in age of marriage and with growing educational attainment. The more education a woman has, the later she tends to marry and have children. Birth rates also have risen for the most educated women, those with at least some college education, while being relatively stable for women with less education. These dual factors have worked together to increase the education levels of mothers of newborns.