Reuters

CHICAGO - Each year, half of American women who would rather not get pregnant will have an unplanned pregnancy, often because they failed to use their contraceptive properly or forgot to use it at all, U.S. researchers said on Tuesday.

As a result, 28 million women in the United States are at risk for an unintended pregnancy, according to the study conducted by the Guttmacher Institute in New York.

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There has been recent attention related to the birth control Ortho-Evra, known as "the patch", and some of the potential risks associated with using it.

Hormonal contraceptives, such as "the pill", "the patch", "the ring", include hormones such as estrogen, which in large doses, may have side effects including blood clots (which is why women are urged not to smoke when on hormonal contraception, as this risk increases even more). Blood clots are rare, but serious and can lead to stroke, and increased doses of estrogen are linked to increased chances of blood clots.