A 30-year-old woman has successfully given birth to a child using an egg she had frozen 12 years ago because she was undergoing a cancer treatment that could have made her unable to reproduce, a researcher who helped her said Friday.

In Japan, it is rare for a woman to give birth with an egg that's been frozen for more than 10 years, although the process is also used to preserve sperm and fertile eggs.

The woman in Aichi Prefecture had her eggs harvested when she was a high school student. They were thawed 12 years later for external fertilization via her husband's sperm. She gave birth to a baby boy in August after the fertilized egg was returned to her uterus.

According to Masashige Kuwayama, a researcher in reproductive technology at Repro-Support Medical Research Centre in Tokyo, the woman developed malignant lymphoma in 2001.

Treating the cancer requires doses of tumor-fighting drugs and a bone-marrow implant, but tumor-fighting drugs can cripple their ability to produce eggs. So he froze two of her eggs just in case.

Before diving into cancer treatment, the woman had two of her eggs harvested and frozen with liquid nitrogen at a Tokyo clinic. The eggs were preserved at 196 degrees below zero.

She overcame the disease a month later after receiving a bone-marrow implant.

"I'm very happy every day after giving birth to my child," the woman said, according to a nonprofit organization that has contact with her.

"I'd like all patients with blood diseases to have hope and receive treatment," she was quoted as saying.