by Jessie Yeung, correspondent, CNN, jyeung@cnn.com

A cancer survivor who became infertile after chemotherapy treatment has given birth to a baby in a world first that’s being hailed as a breakthrough for reproductive science.

The French woman, 34, gave birth after freezing, thawing and fertilizing her immature eggs in a procedure called in vitro maturation (IVM), according to a study published in the journal Annals of Oncology. She had been diagnosed with breast cancer when she was 29.

Doctors have struggled for years to preserve fertility in young cancer patients, with few choices available for patients. One option is to remove ovarian tissue containing immature eggs, then freeze it for future use. However, the woman felt that procedure was too invasive due to her ongoing cancer treatment, said Michael Grynberg, head of the fertility preservation department at the Antoine Beclere University Hospital near Paris, in a news release.

Instead, she chose IVM. Before she began her cancer treatment, doctors removed immature eggs from her ovaries and cryogenically froze them in liquid nitrogen. The eggs were later developed in a laboratory. Five years after the IVM procedure, the woman, who was not named, had recovered from cancer but found herself infertile and unable to conceive for a year, the release said.

Using hormones to stimulate her ovaries might have prompted them to produce more eggs—but it may have also caused the cancer to reappear. Instead, doctors thawed her immature eggs and inseminated them with a sperm injection, before transferring the early-stage embryo into her uterus. In a world-first, the woman then became pregnant and delivered a healthy baby boy named Jules last July.

“We were delighted that the patient became pregnant without any difficulty and successfully delivered a healthy baby at term,” said Grynberg in the release. “This success represents a breakthrough in the field of fertility preservation.”

Until now, no cancer patients had successfully gotten pregnant and given birth using eggs that were frozen and matured this way. The closest thing has been patients whose eggs are removed, immediately fertilized and transferred back into the patient without freezing.

“Getting eggs to mature successfully after removal from the ovary has been a challenge, so this is a very welcome positive step,” said Richard Anderson, head of obstetrics and gynecology at the University of Edinburgh. “This advance is particularly important for cancer patients, but it’s also a step towards easier and less invasive IVF for other women and couples needing assisted reproduction.”

Typically, when women use in vitro fertilization to conceive children, immature eggs are discarded because there has been little scientific evidence that they can be frozen, thawed and matured in a lab, Aimee Eyvazzadeh, a San Francisco-based reproductive endocrinologist, said in 2018. Previous studies and researchers have tried, but with little success. In one 2018 study, scientists in the United States and Britain removed eggs and matured them in the lab—but the eggs appeared to have many abnormalities.

Now, it’s happened. Though this technique isn’t the most common or efficient option, it provides a much-needed second option for cancer patients who face complications—and is a remarkable step forward in fertilization research.