Benefits of Delayed Frozen Embryo Transfer
Delayed frozen embryo transfer at a glance
- Delayed embryo transfer is an option during in vitro fertilization (IVF) in which the fertilized embryos are frozen for future transfer to the woman’s uterus.
- Improvements in the freezing of embryos, including the vitrification process, have made delayed frozen embryo transfers more common.
- Benefits of delayed embryo transfer include reducing pregnancy risks of fresh embryo transfer IVF cycles, permitting the uterus environment to return to normal after egg retrieval, and allowing for genetic screening.
- Delayed embryo transfer often involves freezing all embryos created in an IVF cycle for potential future use, which is referred to as a freeze all IVF cycle.
What is delayed frozen embryo transfer?
An embryo is a female egg fertilized by sperm, and embryos generated in IVF can be either:
- transferred back into the woman’s uterus during the same ovulation cycle in which her egg(s) were retrieved and fertilized (approximately five days after fertilization) – called a fresh-cycle embryo transfer
- or they can be frozen, with their transfer and implantation delayed until a later time – called a delayed or frozen embryo transfer.
In fresh-cycle embryo transfers, the woman’s uterus is still under the influence of fertility medications, resulting in more sensitive ovaries and higher levels of estrogen, which are detrimental to successful embryo implantation.
Previously, delaying embryo transfer until a time when the woman had started a natural ovulation cycle was not a viable option because the freezing process for embryos resulted in less viable embryos and high rates of embryo loss. But with improvements in the vitrification (a flash-freezing technique) and cryopreservation (freezing and storing) process, frozen embryo survival and success rates are now nearly equal to fresh embryos.
Benefits of delayed frozen embryo transfer (freeze all IVF cycle)
Delayed frozen embryo transfer, also called the freeze all technique when a patient freezes all embryos during the first cycle of IVF, has several benefits, including:
- Permits the uterus environment to return to normal after IVF medication, providing natural embryo implantation conditions.
- Reduces the pregnancy risks of fresh embryo transfer IVF cycles, such as preterm labor, preeclampsia and low birth weight.
- Allows for genetic screening, greatly increasing the chances of successful pregnancy and healthy birth.
- Preserves all viable embryos through embryo freezing, making it easier to select single embryo transfer and thus greatly reduce the possibility of multiple gestations (pregnancy of twins or more) and the associated health risks.
- Reduces or removes the risk of ovarian hyperstimulation syndrome (OHSS) during the transfer cycle, which is a risk during fresh-cycle embryo transfers.
- Is less expensive for multiple transfers than repeated fresh IVF cycles.
For more information, make an appointment with one of our reproductive endocrinologists.
More about successful embryo implantation
Successful embryo implantation requires an embryo free of genetic defects, the proper timing so the embryo is in the uterus during the 8-10 day window of implantation after ovulation, and a uterus optimally ready to receive the embryo.
Having a frozen embryo removes the need to transfer an embryo during the same stimulated ovulation IVF cycle when a woman’s eggs are retrieved. This added time, or delayed implantation, increases the chance of a successful pregnancy and birth for these reasons:
- The woman’s uterus has the time to recover from the effects of IVF medications that stimulate egg production but alter the natural environment of the womb. These medications affect the endometrium, the lining of the uterus to which an embryo must implant.
- The woman can return for delayed embryo transplantation during her next or future ovulation cycle. Her uterus will be free of the effects of IVF medications and naturally ready to receive and nurture the embryo.
Time for genetic testing to improve success
Genetic screening, which can be performed on both fresh and frozen/thawed embryos, can identify genetically viable embryos for implantation. Any flaw in the genetic makeup of an embryo is a major cause of implantation failure. This also eliminates the prospect of a child being born with a birth defect or a genetic mutation predisposing the child to health problems.
Preimplantation genetic diagnosis (PGT-M) screens for one specific genetic defect, and is often performed when one (or both) of the parents is known to have, or is suspected of having, a particular genetic defect that may be present in their family history. Preimplantation genetic screening (PGT-A) tests for many possible genetic defects, such as Down syndrome, cystic fibrosis and the BRCA genetic mutations that predispose a mother and her children to ovarian and breast cancers.
Risks of delayed frozen embryo transfer
As with fresh-cycle IVF, IVF with delayed frozen embryo transfer includes risks of:
- Fertility drug side effects
- Ovarian hyperstimulation syndrome and other egg retrieval risks
- Spotting, cramps or discomfort from embryo transfer
- Multiple pregnancy if more than one embryo is implanted
- Learn more about IVF risks.
During embryo freezing or thawing, there is also a slight risk that an embryo will be damaged and need to be discarded. However, IVF with delayed frozen embryo transfer also decreases certain risks associated with fresh-cycle IVF, as highlighted in the benefits section above.