A baby has been born to a cancer survivor from an immature egg that was matured in the laboratory, frozen, thawed and fertilised.
In the first event of its kind, the unnamed woman was left infertile after being treated for breast cancer five years ago.
Before starting chemotherapy, the now 34-year-old had immature eggs removed from her ovaries.
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In vitro maturation (IVM) enabled the eggs to develop in the laboratory.
The news may raise questions about how long frozen eggs should be stored.
Women who elect to freeze their eggs can store them for up to a decade in liquid nitrogen.
Cancer patients at risk of infertility from treatment may be able to store them for up to 55 years.
I saw the 29-year-old patient following her diagnosis of cancer and provided fertility counselling, said Professor Michal Grynberg from the Antoine Bclre University Hospital, near Paris.
I offered her the option of egg freezing after IVM and also freezing ovarian tissue.
She rejected the second option, which was considered too invasive a couple of days after cancer diagnosis.
Freezing ovarian tissue involves taking the outer layer of the organ, which contains a large number of immature eggs.
This allow more eggs to be frozen in one shot under very short notice, according to the Center for Human Reproduction.
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Ultrasound scans revealed the woman had 17 small sacs containing immature eggs in her ovaries, her doctors wrote in the journal Annals of Oncology.
Medically known as an immature ovum, these eggs have not yet undergone the cell division required for fertilisation.
Egg freezing typically involves two weeks of hormonal injections to stimulate the ovaries to produce multiple eggs.
Doctors worried the use of hormones would prolong the process and possibly make her cancer worse.
An emergency procedure was therefore carried out six days later to collect immature eggs before she started chemotherapy.
Once matured, six eggs were frozen in liquid nitrogen, known as vitrification. This rapidly freezes eggs, minimising the development of damaging ice crystals.
Five years later, the woman had beaten her cancer but been unable to conceive for the past 12 months.
Stimulating her ovaries to produce more eggs may have triggered her cancer to return.
The doctors therefore thawed all six eggs, which were fertilised via intracytoplasmic sperm injection (ICSI).
This involves injecting an egg with a womans partners sperm or that of a donor.
Five of the eggs were successfully fertilised, with one embryo being transferred to the womans womb.
She gave birth to her healthy son Jules on 6 July last year.
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This is the first time a cancer patient has gone on to have a successful pregnancy after IVM and vitrification, her doctors claim.
Children have been born as a result of IVM after immediate fertilisation and transfer to the woman, without freezing.
We were delighted the patient became pregnant without any difficulty and successfully delivered a healthy baby at term, said Professor Grynberg.
Egg or embryo vitrification after ovarian stimulation is still the most established and efficient option.
IVM enables us to freeze eggs or embryos in urgent situations or when it would be hazardous for the patient to undergo ovarian stimulation.
This success represents a breakthrough in the field of fertility preservation.
Cancer patients can store their frozen eggs for up to 55 years, compared to 10 years for other women. (Getty Images)
Other experts were also optimistic.
Getting eggs to mature successfully after removal from the ovary has been a challenge, so this is a very welcome positive step, said Professor Richard Anderson from the University of Edinburgh.
It requires a different set of skills to normal IVF, so it isnt widely available, but this report shows it can work, when time is very short.
Freezing eggs at this stage also means they remain the womens own property, without the complication using a partners sperm to fertilise them brings, in that embryos are the couples joint property.
This advance is particularly important for cancer patients, but its also a step towards easier and less invasive IVF for other women and couples needing assisted reproduction.
Professor Alastair Sutcliffe, from the Great Ormond Street Institute of Child Health, said caution must be exercised.
Nevertheless, this new technique could in future be an additional tool for women who have the tragedy of cancer before reproduction to have their own genetic child, he added.
One expert was quick to point out most cancer patients could afford to postpone treatment while they had hormonal injections to freeze their eggs.
Hormonal stimulation usually takes nine-to-11 days and can be started at any time in a womans cycle, and so should delay the start of cancer treatment by no more than two weeks, said Professor Adam Balen from Leeds University Teaching Hospital.
[In] the vast majority of cases, [this wait] has no bearing on the outcome of the treatment.
IVM enables faster progress to cancer treatment as the eggs are matured in the lab and so is a valuable option for those women where a delay could be critical, accepting the lower number of mature eggs that would then be frozen compared with the number anticipated after the stimulation of the ovaries for the collection of mature eggs.
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