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For women using in vitro fertilization to have a child, using either fresh or frozen embryos have similar success rates for most women, according to an international team of researchers.

In a study published Jan. 10 in the New England Journal of Medicine, researchers compared the live birth rates of in vitro fertilization procedures on women who had infertility but otherwise ovulated normally. They found that there was not a significant difference in live births between women who received frozen embryos versus fresh embryos.

Previous research from the team showed that using frozen embryos resulted in more live births among women with polycystic ovarian syndrome -- women who do not ovulate normally -- but the researchers said not as much was known about using fresh versus frozen embryos in women who do ovulate normally.

"This is an important and distinct finding from our previous IVF study, and it suggests that one type of IVF treatment does not fit all, and treatments should be chosen based on specific patient characteristics," said Richard S. Legro, professor of obstetrics and gynecology and public health sciences, Penn State College of Medicine.

The researchers recruited 2,157 women with normal ovulation who were beginning their first round of in vitro fertilization. The women were randomly assigned to receive either fresh or frozen embryos. The researchers then compared the rates of live birth between the two groups.

They found no significant difference in the rates of live births, with the group of women who received frozen embryos having a live birth rate of 48.8 percent while the group receiving fresh embryos had a rate of 50.2 percent.

The researchers also found that using frozen embryos resulted in a lower risk of the woman developing ovarian hyperstimulation syndrome, a condition that sometimes affects women undergoing fertility treatment. Severe cases can result in serious illness or death.

"This study reinforces our previous research by noting that the elective freezing of embryos is safer for all IVF patients (ovulatory and anovulatory) by reducing the risk of ovarian hyperstimulation syndrome," Legro said.

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