Embryo Freezing (Cryopreservation) at Yaal Fertility Centre, Chennai

It once seemed self-evident that a fresh embryo transfer — transferring an embryo in the same cycle it was created — must be better than freezing and thawing. That assumption has not held up, and understanding why explains a great deal about modern IVF.

The problem with fresh transfer is the stimulation cycle itself. To produce multiple eggs, the ovaries are driven hard with hormone medication, and this leaves oestrogen levels far above what occurs in a natural cycle. Those hormone levels also act on the uterine lining, and in some women the endometrium is simply not in an ideal state to receive an embryo at that moment. The embryo may be excellent; the environment it is being placed into is not.

Frozen embryo transfer separates the two. The embryos are created and frozen; then, in a later cycle with no stimulation, the uterine lining is prepared carefully and unhurriedly, and the embryo is transferred when the endometrium is genuinely receptive. The embryo is no longer competing with the after-effects of stimulation.

The result is that FET success rates are comparable to fresh transfer, and in some situations exceed it. FET also carries a lower risk of ovarian hyperstimulation syndrome (OHSS), because pregnancy following a fresh transfer can worsen OHSS in a woman whose ovaries have over-responded — which is why women at high risk are often advised to freeze all embryos and transfer later.

This is not an argument that frozen is always better. It is an argument that freezing is not a compromise or a fallback. Dr. Rukkayal will recommend fresh or frozen transfer based on your response to stimulation, your OHSS risk, and the state of your endometrium — not on a blanket rule.

If you have been through a full IVF cycle, the most striking thing about a frozen embryo transfer is how much less it demands of you.

There is no ovarian stimulation. No high-dose hormone injections, no daily monitoring of follicle growth, no trigger shot. There is no egg retrieval. No sedation, no procedure, no recovery day. The embryos already exist.

What an FET cycle involves instead is preparing the uterine lining. This may be done in a natural cycle — tracking your own ovulation and timing the transfer accordingly — or with medication to build the endometrium in a controlled way. Which approach is used depends on whether your cycles are regular and on your history. You will have a small number of scans to confirm the lining has reached an appropriate thickness.

On the day, the chosen embryo is thawed — surviving in over 95% of cases — and transferred through a fine catheter into the uterus. The transfer takes a few minutes, requires no anaesthesia, and feels much like a smear test. You can go back to normal activity straight away; bed rest is not required and does not improve outcomes.

Then the same two-week wait as any transfer, ending with a beta-hCG blood test.

An FET is therefore substantially cheaper, physically gentler, and less disruptive than a full IVF cycle — which is precisely the point of having frozen embryos in the first place.

Embryos are stored in liquid nitrogen at around −196°C. At that temperature, biological activity effectively ceases — nothing is metabolising, nothing is ageing, nothing is deteriorating. An embryo stored for ten years is, biologically, in the same condition as the day it was frozen.

This is borne out in practice: pregnancy rates from embryos stored for many years are comparable to those stored briefly, and healthy babies have been born from embryos frozen for well over a decade. Duration in storage is not, in itself, a risk factor.

What matters far more than storage time is the age you were when the embryos were created. An embryo made when you were 32 remains a 32-year-old embryo, however long it sits in the tank. This is what makes freezing so valuable: it preserves the quality of that moment.

Storage is renewed annually, and there are practical and legal matters attached to it — consent, storage duration limits, and what happens to embryos you no longer intend to use. These are covered in the section below, and they are more consequential than most couples expect.

This is the part of embryo freezing that clinics tend to skip and that couples most wish they had understood at the outset. It deserves to be said clearly.

An embryo is created from both partners’ gametes, and both partners normally have a say in what happens to it. This is the fundamental difference between freezing embryos and freezing eggs. Frozen eggs remain solely yours, and you can later choose whom to have a child with. A frozen embryo already involves a specific partner — and consent from both parties is normally required to use it.

The implications only become apparent when circumstances change. If a couple separates, or if one partner withdraws consent, the embryos generally cannot be used by the other. This has been the subject of painful and well-publicised legal disputes elsewhere in the world, and it is not a hypothetical concern. Couples who freeze embryos while in a stable relationship rarely imagine that they might one day disagree about them.

There are also decisions you will eventually have to make about embryos you do not use. Broadly, the options are to continue storing them, to allow them to perish, to donate them to another couple, or to donate them to research — where permitted. Most couples find these decisions considerably harder than they expected, and it is common to defer them for years by continuing to pay storage fees.

None of this is a reason not to freeze embryos. It is a reason to discuss the consent forms properly rather than signing them in a hurry, and to know that if you are single, or unsure about your relationship, egg freezing may be the more appropriate choice precisely because it keeps that decision open.

Embryo storage and consent in India are governed by the ART (Regulation) Act, 2021. Our team will take you through exactly what you are consenting to before anything is frozen.