The National Center for Health Statistics maintains an extensive databse of information about pregnancy and birth in the United States. The statistics for 200 reflect the boom in "late-timing" motherhood.

Birthrates for older women have increased dramatically in recent years. Of the 4,058,814 babies born in the United States in 2000, 452,057 were to women 35 to 39; 90,013 to women 40 to 44; 4,349 to women 45 to 49; and 255 to women 50 to 54. Still, birthrates for older women haven't matched historical levels: In 1960, the birthrate for women 40 to 44 was less than 20 per 1,00 births—more than twice the current rate.

More first babies are being born to older mothers, with women over age 30 accounting for 24 percent of all first-time mothers in 2000. (In 1975, they accounted for just 5 percent of first-time mothers.)

More twins and triplets are being born to older mothers, with multiple birthrates rising steadily for women over 40 and 45. In 2000, 40 percent of all births to women 50 and older were twins or triplets. (Overall, twin births have increased 74 percent from 1980 to 2000.)

More older mothers are single. In fact, birthrates for older, unmarried women have more than doubled since the year 1980.