How long can an embryo remain frozen, and does this affect the chances of success?

A patient once asked me if her embryos, frozen seven years earlier, were ‘still good’. This is a common question, and it is based on an understandable but mistaken assumption: the idea that a frozen embryo ages like food in a freezer. That is not what happens.

What happens at −196 °C

Embryos are stored in liquid nitrogen at −196 °C. At this temperature, all biological activity is suspended: there is no metabolism, no cell division and no ageing. The critical stages occur at just two points – freezing and thawing – when the cells pass through the temperature ranges where ice crystals form.

This is where the technique comes into play. Since the late 2000s, most laboratories have been using vitrification, an ultra-rapid freezing method that transforms the medium into a kind of crystal-free glass. It has largely replaced the slow freezing method previously used. The difference is most evident during thawing.

A meta-analysis of seven randomised trials, published in 2017, confirmed the advantage of vitrification over slow freezing in terms of embryo survival upon thawing. With vitrification, the vast majority of blastocysts survive thawing. This is what has made freezing a standard part of IVF, and sometimes the strategy of choice.

Does the duration of freezing affect the chances of success?

This is the most widely studied question, and the results are generally reassuring, with one caveat for periods exceeding five years.

• A study of 8,736 thawed vitrified blastocysts, stored for up to eight years, found no difference in birth rates based on duration, nor any effect on birth weight or malformations.
• A meta-analysis published in 2022, involving more than 18,000 embryos, found no difference in survival, birth rates or birth defects beyond twelve months’ storage.
• A Spanish study published in 2024, involving 58,001 vitrified blastocysts over a period of eleven years, found no link between storage duration and live births; however, three-quarters of the embryos had been stored for less than three years.
• A few studies, mainly Chinese and single-clinic, have, however, observed lower birth rates following longer storage, particularly beyond five years. One such study, published in 2024 and covering 36,665 transfers with storage periods of up to 9.5 years, found fewer implantations and births beyond five years, even for good-quality blastocysts. One possible explanation is that the best embryos are generally transferred first: those that remain frozen for a long time are, on average, of slightly lower quality. Indeed, a study of 2,688 transfers of chromosomally normal embryos found no effect of storage duration once this bias was taken into account.

In practice, there is no reason to consider an embryo that has been vitrified for two, five or eight years to be ‘past its best’, although a modest effect beyond five years cannot be ruled out. The factor that really matters remains the woman’s age at the time the egg was retrieved, not the time spent in liquid nitrogen. All these studies are retrospective: they offer reassurance, without proving everything.

Known records

In October 2022, twins were born in the United States from embryos frozen in April 1992, more than thirty years earlier. In July 2025, a boy was born, again in the United States, from an embryo frozen in May 1994 using the ‘slow’ method of the time: this was then the longest known period. These births, resulting from embryo donations, are exceptional cases; they say nothing about average chances, but show that a well-preserved embryo can remain viable for decades. Embryo donation in Greece is described in the dedicated article.

What Greek law permits

Greek law stipulates a retention period of five years, which may be extended in five-year periods under Law 4958/2022, subject to a written request before the expiry date. If no request for an extension is made, the option selected in your consent form will apply. The annual cost, the options at the end of the project and the pitfalls of consent are detailed in the article on embryo storage.

Rules vary considerably from one country to another. In the UK, for example, the maximum storage period has been extended to 55 years, with consent required to be renewed every ten years. If your embryos are stored in Greece, Greek law applies, even if you live elsewhere. And if you wish to have them transferred to another country, see the transport of embryos between countries.

What to ask about older embryos

• Which technique was used to freeze them: vitrification or slow freezing?
• At what stage: Day 2–3 embryo or Day 5–6 blastocyst?
• How many straws, and how many embryos per straw?
• Does the laboratory have the expertise to thaw slowly frozen embryos, if that is your case?

This information is normally included in the laboratory report. If you do not have it, or if the document is in Greek, please write to me: I will request it from the clinic.

Frequently asked questions

Source: https://fertilitegrece.com/en/blog/how-long-can-embryos-be-frozen/ — Triada Baloukoudis, IVF patient coordination in Greece. General information, not medical or legal advice. Printed on

Triada Baloukoudis
Independent IVF patient coordinator in Thessaloniki, with 24 years of experience supporting patients travelling from abroad. More · Contact · Facebook