A baby is believed to be the first in the world to be born after eggs were taken from his mother and matured in a lab before being frozen, scientists said.
They said the arrival of baby Jules is the first reported case of a baby born after immature eggs were grown outside of the mother and then thawed, fertilised and implanted years later.
Fertility doctors took eggs from the mother, a then 29-year-old French woman, before she started chemotherapy for breast cancer.
But there was not enough time for her to be given ovarian stimulation hormones to help her produce mature eggs that could be frozen.
Instead, the experts removed seven immature eggs from her ovaries and used a technique called in vitro maturation (IVM) to help them to develop further in the laboratory.
They say the case offers hope to women who would like to have children after a cancer diagnosis, but for whom ovarian stimulation is hazardous.
The method also avoids the risk of “re-seeding the cancer”, which can happen in some cancers when ovarian tissue is later transplanted back into a cancer patient.
Until now, there have been no successful pregnancies in cancer patients after eggs that have undergone IVM and then been frozen, although some children have been born as a result of IVM followed by immediate fertilisation and transfer to the patient without freezing.
Professor Michael Grynberg, head of the Department of Reproductive Medicine and Fertility Preservation at the Antoine Beclere University Hospital, near Paris, said: “We were delighted that the patient became pregnant without any difficulty and successfully delivered a healthy baby at term.
“My team and I trusted that IVM could work when ovarian stimulation was not feasible.”
He added: “This success represents a breakthrough in the field of fertility preservation.”
The case has been outlined in a letter in the cancer journal Annals of Oncology.
After maturing, the eggs were then frozen by vitrification, which freezes the eggs very rapidly in liquid nitrogen to reduce the chances of ice crystals forming and damaging the cell.
Five years later, when the woman had recovered from her cancer, she discovered the treatment had left her infertile.
She and her doctors decided to use the frozen eggs, five of which were fertilised successfully after being thawed.
One embryo was transferred to the patient’s womb, and nine months later she gave birth to a healthy boy on July 6 2019.
Prof Grynberg said egg or embryo vitrification after ovarian stimulation is still the most established and efficient option, but that his team’s success gives women another option.
He continued: “IVM enables us to freeze eggs or embryos in urgent situations or when it would be hazardous for the patient to undergo ovarian stimulation.
“In addition, using them is not associated with a risk of cancer recurrence.
“We are aware that eggs matured in the lab are of lower quality when compared to those obtained after ovarian stimulation.
“However, our success with Jules shows that this technique should be considered a viable option for female fertility preservation, ideally combined with ovarian tissue cryopreservation as well.”