Some women have to undergo fertility treatments to get pregnant, but according to a new study by the CDC, about a third of the babies born in the past 30 years weren't planned -- and it should come as no surprise that more than half of those pregnancies are tied to a lack of contraception use.

While "oops" pregnancies are down among white women, researchers say the number of unintended births has remained steady since 1982: they account for 37 percent of all babies born in the US.

"Unintended births occur disproportionately among non-Hispanic black women, unmarried women, and women with less income and education," the report states. It goes on to say that education in particular seems to make a difference -- for example, 35 percent of unplanned pregnancies occurred in women without a high school diploma, while only 7 percent occurred in college graduates.

Overall, never-married women and Hispanic women now account for a growing number of births, and 60 percent of women who experienced an unplanned pregnancy between 1998 and 2002 were not using contraception. And startlingly, more than a third of those women didn't think they could get pregnant.

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