BEIJING -- Xiaoxin (pseudonym), an 11-year-old child suffering from leukemia, successfully underwent an ovarian tissue freezing operation before a bone marrow transplant recently in the Peking University People's Hospital (PKUPH).

The operation, or ovarian tissue cryopreservation, saved her ability to get pregnant in the future by preserving her ovarian tissue at a low temperature.

The current fertility preservation techniques include egg freezing, embryo freezing, sperm freezing, and ovarian tissue freezing, which is also the sole option to preserve fertility for prepubescent girls, said Tian Li, deputy head of the hospital's obstetrics and gynecology department.

This technique is suitable for female patients urgently needing surgery, radiotherapy, or chemotherapy, which may cause ovarian damage or premature ovarian failure, she added.

During such an operation, doctors take tissues, where many follicles are stored, from the ovarian cortex and freeze them in liquid nitrogen at minus 196 degrees Celsius. After the patients' disease improves, their ovarian tissues get unfrozen and transferred back into their bodies to recover endocrine and ovulation functions.

Xiaoxin was diagnosed with chronic myeloid leukemia, a type of cancer that produces many immature white blood cells and inhibits regular blood production in the bone marrow, at the PKUPH six months ago.

Chemotherapy and a bone marrow transplant became urgent for her, but they would directly result in the loss of her fertility.

For female bone marrow transplant patients of childbearing age, the incidence rate of premature ovarian insufficiency, a decline of normal ovarian function before the age of 40, is nearly 100 percent after they received myeloablative chemotherapy, said Yang Xin, an expert with the obstetrics and gynecology department of the PKUPH.

She explained that high doses of chemotherapy might cause premature ovarian failure, leading to the loss of fertility.

Xiaoxin eventually underwent the ovarian tissue freezing operation lasting several hours after experts from the hospital's departments of obstetrics and gynecology, hematology, and pediatrics jointly confirmed the feasibility of the operation.

"It is the best way for Xiaoxin to get her endocrine and ovulation functions recovered after the bone marrow transplant," said Wang Jianliu, deputy head of the PKUPH.

Besides the current ovarian tissue freezing technology, researchers have made constant breakthroughs in female fertility preservation methods in China.

A group of scientists from the University of Science and Technology of China published their new findings in the journal Nature Communications last December, revealing a new method to preserve mouse follicles at a low temperature.

The method was vitrification cryopreservation of follicles encapsulated in hydrogel by "nanowarming," a novel cryopreservation technology. Compared with conventional methods, it increased the viability of follicles by more than 30 percent after recovery, shedding light on a promising approach for fertility preservation in women.

According to the research team, the patent for their new technology has been filed and is expected to be applied clinically in related hospitals in east China's Anhui Province this year.