When undergoing IVF treatment, patients are often advised to choose between a fresh embryo transfer or a frozen embryo transfer (FET). With modern advances in cryogenic technology, frozen embryo transfers are now widely used and carefully studied.
But what’s the difference – and does freezing embryos affect pregnancy outcomes?
What Is a Fresh Embryo Transfer?
A fresh embryo transfer takes place in the same IVF cycle as egg retrieval.
How it works:
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Eggs are collected and fertilised
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Embryos are cultured for several days
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An embryo is transferred into the uterus without freezing
Fresh transfers offer a shorter timeline, but they occur while the body is still responding to ovarian stimulation medications.
What Is a Frozen Embryo Transfer (FET)?
A frozen embryo transfer involves freezing embryos after fertilisation and transferring them in a later cycle.
How it works:
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Embryos are frozen using vitrification
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Stored in cryogenic conditions
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Transferred weeks, months, or even years later
FET allows the uterus to be prepared in a more controlled environment and offers greater flexibility in treatment timing.
Does Freezing Affect Embryo Quality?
Modern freezing methods use vitrification, which rapidly freezes embryos and prevents ice crystal formation.
Studies consistently show that:
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Frozen embryos have high survival rates
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Freezing does not damage embryo quality
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Pregnancy and live birth rates are comparable to fresh transfers
In some cases, outcomes with frozen transfers are even slightly improved.
IVF Success Rates: Frozen vs Fresh
Research comparing frozen and fresh embryo transfers has found:
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Similar or higher pregnancy rates with frozen embryo transfers
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Lower risk of ovarian hyperstimulation syndrome (OHSS) with frozen cycles
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Potentially better uterine receptivity, as hormone levels have time to normalise
For these reasons, many clinics now use a “freeze-all” approach in certain cases.
Pregnancy Outcomes
Large studies show:
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No significant difference in miscarriage rates
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Comparable neonatal outcomes
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Slightly higher average birth weights reported in some frozen-transfer pregnancies
Both methods can result in healthy pregnancies when performed under proper clinical conditions.
Why Clinics May Recommend Frozen Transfers
Frozen embryo transfer may be recommended when:
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Hormone levels are elevated during stimulation
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Genetic testing (PGT) is planned
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Patients require flexibility in timing
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Embryos need to be stored or transported internationally
Frozen embryos can remain safely preserved for long periods without compromising viability.
Frozen Embryos and International IVF
Frozen embryos play a key role in cross-border fertility care. With appropriate cryogenic storage and experienced handling, embryos can be:
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Stored long-term
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Transported internationally
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Transferred at the most suitable time for the patient
Final Thoughts
Both fresh and frozen embryo transfers are safe and effective options in modern IVF treatment. Advances in freezing technology have made frozen embryo transfer a reliable and widely used approach, offering flexibility without compromising success rates.
The best option depends on individual medical factors and should always be guided by a fertility specialist.
References & Studies
- Roque M. et al. (2019) https://academic.oup.com/humupd/article/25/5/592/5480051
- Shapiro B.S. et al. (2014) https://pubmed.ncbi.nlm.nih.gov/24656307/
- ESHRE Guidelines (European Society of Human Reproduction and Embryology) https://www.eshre.eu/Guidelines-and-Legal/Guidelines
- CDC – Assisted Reproductive Technology Reports (USA) https://www.cdc.gov/art/
- HFEA (UK Fertility Regulator) https://www.hfea.gov.uk/