St. Louis doctors successfully transplanted a full ovary that allowed the donor's infertile twin sister to give birth to baby girl on Thursday.

Researchers say that this is the first time that this operation has resulted in live birth.

This may be a new method of preserving fertility for cancer patients or women who prefer to start families later in life, according to the New England Journal of Medicine.

Women who are in their 20s are able to preserve one of their ovaries for future use. "If she's 40 or 45 when she has it transplanted back, it's still a 25- or 30-year-old ovary, so she's preserving her fertility," said Dr. Sherman Silber of the Infertility Center. "We've actually done it for quite a few patients. I think there will be many more women who will want to do that."

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