Frozen Embryo Transfer

Why transfers are often frozen rather than fresh

Freezing embryos and transferring them in a later cycle has become routine rather than a fallback. Vitrification — very rapid freezing — has made survival rates high, which changed the calculation.

A frozen transfer separates the stimulation from the transfer. The uterine lining is prepared in its own cycle, without the high hormone levels that stimulation produces, and there is time for genetic test results to come back where testing is part of the plan.

• Surplus good-quality embryos remain after a fresh transfer
• PGD/PGT results are awaited before choosing an embryo
• There is a risk of ovarian hyperstimulation, making a fresh transfer unwise
• Hormone levels or the lining are not optimal in the stimulation cycle
• Treatment is being deliberately deferred for medical or personal reasons

The three types of FET cycle

None of these is inherently better. The right one depends on your cycle, hormone levels and history, and your specialist will explain why they are recommending a particular approach.

• Natural cycle — for women ovulating regularly. The cycle is tracked by scan, ovulation is identified, and transfer is timed to it with minimal or no medication.
• Modified natural cycle — much the same, with a trigger injection used to fix the timing of ovulation precisely.
• Medicated cycle — oestrogen and progesterone prepare the lining without relying on ovulation. This is used where cycles are irregular or where precise scheduling is needed.

What the transfer day involves

The embryo is thawed on the day of transfer and assessed for survival. The transfer itself takes a few minutes: a fine catheter passes the embryo into the uterus under ultrasound guidance. No sedation is needed and most women describe it as painless.

You can return to normal activity the same day. Extended bed rest has not been shown to improve outcomes. A blood pregnancy test follows about two weeks later, and progesterone support usually continues until then and often beyond.

Storage, survival and what to expect

Vitrified embryos survive thawing in the large majority of cases, though not every embryo does, which is why survival is confirmed on the day. Embryos do not deteriorate with time in storage; an embryo frozen several years ago is not a worse embryo than one frozen last month.

Storage duration, renewal and consent are agreed in writing before freezing, and we will contact you before any storage period ends.

Frequently asked questions