A woman who was left infertile by cancer treatment has given birth to a baby after her immature eggs were collected, matured in a lab and frozen for use five years later.

Fertility specialists at Antoine Béclère University hospital in Clamart near Paris said the healthy boy, named Jules, was the first baby to be born through the new procedure.

The unnamed woman was offered fertility counselling when she was about to embark on a course of chemotherapy for breast cancer at the age of 29. The drugs used in many cancer treatments are known to put fertility at risk.

Doctors ruled out the standard IVF procedure of using hormones to stimulate the woman’s ovaries to produce eggs, concerned it might exacerbate her cancer. Another option was to remove and freeze some of the patient’s ovarian tissue and reimplant it when she had recovered, but the woman considered the operation too invasive.

Instead, the woman opted for retrieval of early-stage eggs from her ovaries. These were matured in the lab for one or two days and then vitrified – a process that freezes the cells rapidly in nitrogen to reduce the chances of ice crystals forming and rupturing them.

The woman recovered from cancer but found she could not get pregnant naturally and returned to the hospital for fertility treatment. There, Grynberg’s team thawed seven frozen eggs, six of which survived the process.

These were fertilised with sperm injections, but only one developed into a healthy embryo that gave rise to the successful pregnancy. The boy was born on 6 July 2019 when the woman was 34.