What Is a Fresh Embryo Transfer?
A fresh embryo transfer takes place during the same IVF cycle in which the eggs are retrieved.
The basic sequence is:
- Ovarian stimulation
- Follicle monitoring
- Egg retrieval
- Fertilisation
- Embryo development
- Fresh embryo transfer
- Pregnancy testing
Embryos are usually transferred after several days of laboratory development.
Because the transfer occurs during the same cycle as ovarian stimulation, the patient does not need to undergo a separate cycle to prepare the uterus for the transfer.
What Is a Frozen Embryo Transfer?
A frozen embryo transfer (FET) involves using an embryo that was created during an earlier IVF or ICSI cycle and subsequently cryopreserved.
The embryo is thawed and transferred into the uterus during a later cycle.
Depending on the patient’s menstrual cycle, a frozen transfer may be performed using:
- A natural cycle
- An ovulation-induced cycle
- A hormonally regulated cycle
For a natural-cycle transfer, ovulation is monitored and the timing of embryo transfer is coordinated with the woman’s natural hormonal changes.
For a regulated cycle, medication is used to prepare the uterine lining before the embryo is transferred.
What Is the Main Difference Between Fresh and Frozen Transfer?
The biggest difference is when the embryo is transferred.
Fresh Embryo Transfer
The embryo is transferred during the same treatment cycle as:
- Ovarian stimulation
- Egg retrieval
- Fertilisation
Frozen Embryo Transfer
The embryo is:
- Created during an IVF or ICSI cycle
- Cryopreserved
- Stored
- Thawed at a later date
- Transferred during a subsequent cycle
A frozen transfer therefore separates embryo creation from embryo transfer.
Fresh vs Frozen Embryo Transfer at a Glance
| Factor | Fresh Embryo Transfer | Frozen Embryo Transfer |
| When does transfer occur? | During the same IVF cycle | During a later cycle |
| Egg retrieval required immediately before transfer? | Yes | No |
| Embryo freezing required? | No | Yes |
| Requires a separate transfer cycle? | No | Yes |
| Ovarian stimulation in transfer cycle | Yes | Usually no |
| Can use embryos from an earlier IVF cycle? | No | Yes |
| Can reduce OHSS risk by avoiding fresh transfer? | No | Yes |
| May delay pregnancy attempt? | Usually less | Usually more |
| Can use remaining frozen embryos later? | Additional embryos may be frozen | Yes |
The specific treatment schedule can vary depending on the fertility centre and the patient’s circumstances.
How Does a Fresh Embryo Transfer Work?
A fresh transfer follows the initial stages of IVF.
Ovarian Stimulation
Medication is used to encourage the development of multiple ovarian follicles.
The ovaries are monitored through ultrasound and, where appropriate, blood tests.
Egg Retrieval
When the follicles are ready, medication is used to trigger final egg maturation.
Egg retrieval is then performed, usually around 36 hours later depending on the treatment protocol.
Fertilisation
The retrieved eggs are fertilised with sperm using either:
- Conventional IVF
- ICSI when clinically appropriate
Embryo Culture
The resulting embryos are monitored in the laboratory.
Embryos may be cultured for several days before transfer.
Fresh Embryo Transfer
A suitable embryo is transferred into the uterus using a thin catheter.
The transfer is usually a short procedure and does not require abdominal surgery.
Hormonal support, commonly involving progesterone, may be prescribed after transfer.
How Does a Frozen Embryo Transfer Work?
A frozen transfer follows a different sequence.
Embryo Creation
The embryos are created during a previous IVF or ICSI cycle.
Suitable embryos are then cryopreserved.
Preparing the Uterine Lining
The uterus needs to be prepared for embryo implantation.
Depending on the patient’s menstrual cycle, this may involve:
- Monitoring natural ovulation
- Ovulation induction
- Hormonal medication
Thawing the Embryo
The selected embryo is thawed in the laboratory before transfer.
Not every embryo will necessarily survive the thawing process, although modern cryopreservation techniques have made embryo freezing an established part of IVF treatment.
Embryo Transfer
The thawed embryo is transferred into the uterus using a thin catheter.
The patient does not need to undergo another egg retrieval for the frozen embryo.
Why Might Doctors Recommend a Frozen Embryo Transfer?
There are several reasons why a fertility specialist may recommend freezing embryos rather than performing a fresh transfer.
High Risk of OHSS
One of the clearest reasons to consider a freeze-all approach is when a patient is at increased risk of ovarian hyperstimulation syndrome (OHSS).
OHSS can occur when the ovaries respond excessively to fertility medication.
Avoiding a fresh transfer can reduce the risk of late-onset OHSS because pregnancy-related hormonal changes can prolong or worsen the condition.
Hormone Levels Are Not Ideal for Fresh Transfer
During ovarian stimulation, hormone levels can become substantially different from those seen during a natural menstrual cycle.
In some patients, the fertility team may determine that the hormonal environment is not ideal for immediate embryo transfer.
The embryos can instead be frozen and transferred during a later cycle when the uterine lining can be prepared under more suitable conditions.
The Uterine Lining Needs More Preparation
An ultrasound may show that the endometrium is not developing as expected.
Depending on the circumstances, the transfer may be postponed while the uterine lining is prepared during another cycle.
Pre-Implantation Genetic Testing Is Planned
If embryos are undergoing certain forms of pre-implantation genetic testing, they need to be biopsied and frozen while the laboratory performs the testing.
A fresh transfer is therefore not performed during the same cycle.
The embryo transfer can take place later once appropriate results are available.
Additional Embryos Are Available
An IVF cycle may produce more than one embryo suitable for cryopreservation.
These embryos can potentially be used in subsequent frozen transfer cycles without repeating ovarian stimulation and egg retrieval.
Why Might a Fresh Embryo Transfer Be Considered?
Fresh transfer also has potential advantages.
Transfer Can Occur Sooner
Because the embryo is transferred during the same IVF cycle, there is no need to wait for a subsequent menstrual cycle to prepare the uterus.
This can reduce the overall time before attempting embryo transfer.
No Embryo Freezing Is Needed for the Transferred Embryo
The embryo does not need to undergo a freeze-thaw process before transfer.
It May Be Appropriate for Some Patients With Lower Ovarian Response
Research suggests that treatment strategies may perform differently according to a patient’s prognosis.
For example, a 2025 randomised trial involving women with a low prognosis for IVF found higher live birth rates with fresh transfer than with a freeze-all strategy in that particular population. This does not mean fresh transfer is generally better, but it reinforces the importance of individualising the decision.
Does Frozen Embryo Transfer Have a Higher Success Rate?
Not necessarily.
This is one of the most common misconceptions about fresh versus frozen transfer.
Research comparing a conventional IVF strategy with a freeze-all strategy has generally not shown a clear overall advantage in cumulative live birth rates for one approach over the other.
However, outcomes can differ between patient groups.
For example, patients at high risk of OHSS may benefit from avoiding a fresh transfer, while certain lower-prognosis patients may have different outcomes.
The decision should therefore not be based on the assumption that frozen embryos are inherently more likely to result in pregnancy.
Does Freezing Affect Embryo Quality?
Embryo cryopreservation allows suitable embryos to be stored for later use.
Modern vitrification techniques have made embryo freezing a routine part of many IVF programmes.
However, embryo survival after thawing is not guaranteed.
The quality and developmental potential of the embryo before freezing remain important.
Embryo quality is influenced by factors such as:
- Egg quality
- Sperm factors
- Maternal age
- Embryo development
- Laboratory conditions
A frozen embryo is not necessarily inferior to a fresh embryo simply because it has been frozen.
Is a Frozen Embryo Transfer More Comfortable?
The physical experience is different rather than necessarily more or less comfortable.
A frozen transfer does not require:
- Ovarian stimulation
- Egg retrieval
- Another collection of eggs
The transfer itself is similar to a fresh embryo transfer.
However, depending on the type of frozen transfer cycle, the patient may need hormonal medication or additional monitoring before the embryo is transferred.
How Is the Uterus Prepared for a Frozen Transfer?
There are several approaches.
Natural Cycle
A natural cycle may be suitable for women who ovulate regularly.
The fertility team monitors:
- Follicle development
- Ovulation
- Hormonal changes
The embryo transfer is then timed according to ovulation.
Ovulation-Induced Cycle
Medication may be used to stimulate ovulation in women who do not ovulate consistently.
The timing of the embryo transfer is coordinated with the induced ovulation.
Hormone-Regulated Cycle
Medication is used to prepare the endometrium.
This may involve:
- Oestrogen
- Progesterone
The fertility team monitors the uterine lining and determines when the embryo should be transferred.
The most appropriate approach depends on the patient’s menstrual cycle and medical history.
Are There Risks Associated With Frozen Embryo Transfer?
FET is an established fertility treatment, but it is not risk-free.
Potential considerations include:
- Failure of the embryo to survive thawing
- Failure of implantation
- Pregnancy loss
- Ectopic pregnancy
- Pregnancy complications
Research has also raised questions about differences in pregnancy-related risks between fresh and frozen transfer.
Some studies and reviews have found that frozen transfer may be associated with a higher risk of certain hypertensive pregnancy disorders and large-for-gestational-age birth compared with fresh transfer. The evidence and magnitude of these differences vary, so they should be discussed in the context of the patient’s individual circumstances.
Can Frozen Embryos Be Used Years Later?
Potentially, yes, provided the embryos remain appropriately stored and applicable regulations and consent requirements are met.
The benefit of embryo cryopreservation is that embryos created during one IVF cycle can potentially be used during later transfer cycles.
This means patients may be able to attempt another pregnancy without undergoing ovarian stimulation and egg retrieval again.
In Singapore, storage arrangements and applicable limits should be discussed with the fertility centre.
Is a Frozen Embryo Transfer Considered Another IVF Cycle?
The terminology can sometimes be confusing.
A frozen embryo transfer does not involve another round of ovarian stimulation and egg retrieval, but it is a separate frozen ART cycle for the purposes of Singapore’s public co-funding framework.
Eligible couples can currently receive government co-funding for up to three fresh and three frozen ART cycles at public assisted reproduction centres, subject to the applicable eligibility criteria and funding caps.
The cost of a frozen transfer is generally lower than a fresh ART cycle because it does not involve the full process of ovarian stimulation, egg retrieval and fertilisation.
Which Is Better: Fresh or Frozen Embryo Transfer?
There is no universal answer.
A fertility specialist may recommend fresh transfer when:
- The ovarian response is appropriate
- OHSS risk is low
- The uterine lining is suitable
- Hormonal conditions are considered appropriate
- There is no need for genetic testing before transfer
A frozen transfer may be preferred when:
- OHSS risk is elevated
- Hormone levels or the uterine environment are not considered suitable for fresh transfer
- PGT requires embryo freezing
- Additional embryos are available
- A later transfer is considered more appropriate for the patient’s circumstances
The objective is to choose the approach that provides an appropriate balance between treatment effectiveness, safety and timing.
Does a Fresh Transfer Mean You Will Get Pregnant Faster?
Potentially, because the embryo transfer occurs during the same treatment cycle.
However, pregnancy is not guaranteed.
With a frozen transfer, embryo transfer is delayed until a later cycle.
The delay may be worthwhile if it allows the fertility team to reduce OHSS risk, optimise the uterine lining or complete genetic testing.
Therefore, the shortest route to embryo transfer is not necessarily the most appropriate route to a healthy pregnancy.
What Happens If You Have More Than One Embryo?
If multiple suitable embryos are available, the fertility team may recommend transferring one embryo and freezing the others for future use.
Single embryo transfer can reduce the risk of multiple pregnancy while allowing remaining embryos to be used in subsequent cycles.
The number of embryos recommended for transfer depends on factors such as:
- Age
- Embryo development
- Previous IVF outcomes
- Embryo genetic status where relevant
- Applicable clinical guidance and regulations
Transferring multiple embryos can increase the risk of twins or higher-order multiple pregnancies.
What Factors Does a Fertility Specialist Consider?
The decision between fresh and frozen transfer may take into account:
Age
Age can affect egg quality, embryo development and expected IVF outcomes.
Ovarian Response
Patients who produce a large number of follicles may have a higher risk of OHSS.
Hormone Levels
Hormonal changes during ovarian stimulation may influence whether immediate transfer is appropriate.
Uterine Lining
The endometrium needs to be appropriately prepared for implantation.
Embryo Development
The number and quality of embryos available can influence the treatment plan.
Previous IVF Treatment
Previous treatment outcomes may help guide decisions about future cycles.
Genetic Testing
Embryos undergoing certain forms of genetic testing need to be frozen while testing is completed.
Patient Preferences
The timing, cost, medication requirements and emotional considerations of treatment may also form part of the discussion.
Fresh vs Frozen Embryo Transfer in Singapore
For couples undergoing assisted reproductive treatment in Singapore, the choice between fresh and frozen transfer is both a clinical and practical consideration.
The current public co-funding framework distinguishes between fresh and frozen ART cycles. Eligible couples can receive co-funding for up to three fresh and three frozen ART cycles, subject to the prevailing eligibility requirements and funding caps.
However, financial considerations should not determine the medical choice on their own.
The fertility team will generally consider the patient’s clinical circumstances first, including ovarian response, OHSS risk, embryo development and the condition of the uterine lining.
Patients should also check the latest funding rules because Singapore’s fertility financing policies may change over time.
Fresh and frozen embryo transfers are two established approaches used after IVF or ICSI.
With a fresh embryo transfer, the embryo is transferred during the same cycle as ovarian stimulation and egg retrieval. With a frozen embryo transfer, the embryo is cryopreserved and transferred during a later cycle.
Neither approach is universally better. Current evidence suggests that a freeze-all strategy does not consistently improve cumulative live birth rates across the general IVF population, but it can reduce the risk of OHSS in patients who are at risk. The choice may also be influenced by hormone levels, uterine lining, embryo testing, ovarian response and previous treatment.
A frozen transfer also provides the option of using embryos created during an earlier IVF cycle without repeating ovarian stimulation and egg retrieval. However, it delays embryo transfer and requires a separate treatment cycle.
Ultimately, the choice between fresh and frozen embryo transfer should be individualised. A fertility specialist can assess the patient’s ovarian response, embryo development, uterine environment and overall health before recommending the approach that best fits the treatment plan.
This article is for general information only and should not replace medical advice from a qualified healthcare professional.
