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There are fewer people eligible to be on MTV's Teen Mom, according to the latest stats from the U.S. Centers for Disease Control and Prevention. The report shows a continued decline in single motherhood, in all groups but the over-35 segment. Now, only 4 out of every 10 births occur out of wedlock—and more than half of those "single mom" births are within cohabiting couples who just haven't decided to make their union official.

The biggest decline in birth rate occurred in the 15-to-17-year-old age bracket, where the number of births fell by almost a third over the last five years—and the older-teen birth rate also declined by more than 25 percent.

This slightly contradicts some earlier figures in a Johns Hopkins study, which showed that nearly 60 percent of births to the Millennial generation had occurred out of wedlock.

Still, both sets of data show that the wife-then-mom model may not be the scenario for many modern-day moms.

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