Embryo Freezing or vitrification has not only improved embryo survival rates but has benefited couples financially and psychologically.
Artificial Reproductive Technology ( ART ) or specifically In-Vitro Fertilization (IVF), gave the world our first IVF baby in 1978. The birth of Louise Brown gave infertile couples a new hope towards parenthood. Over the last 3 decades, IVF technology has evolved and advanced.Ovarian stimulation has become safer and more patient-friendly. Fertility laboratory techniques have improved tremendously.
The most important breakthrough development in the fertility laboratory technique is the ability to freeze and thaw embryos successfully.The original method of freezing and thawing the embryos is associated with higher embryo loss.
The current technique of embryo freezing known as vitrification has improved the embryo survival rate. In an established IVF laboratory, the survival rate of thawed embryos with vitrification technique is close to one hundred percent.
In 1984, the first baby via frozen embryo transfer (FET) was born. Since then, many fertility clinics have adopted frozen embryo transfer as part of their strategy in their IVF protocol.
Embryo transfer procedure can be divided into fresh and frozen embryo transfer based on the timing of the embryo transfer. In a fresh embryo transfer, embryos are typically replaced into the womb between two and five days after the egg collection procedure in the same period cycle.
In a frozen embryo transfer (FET), embryos are frozen between day two and six after an egg collection. The embryo/s is /are transferred into the womb at a later date either in a natural period cycle or after the womb is prepared with medication.
What are the benefits of frozen embryo transfer (FET)?
a) Higher pregnancy rate
FET offers a higher pregnancy rate compared to fresh embryo transfer, especially for women who are more than 35 years old. For younger women, FET gives a similar if not higher pregnancy rate compared to fresh embryo transfer.
Every couple, regardless of their age, wants the highest pregnancy rate for their age in an IVF treatment. FET can help them achieve it. So if you are going through an IVF, discuss advantage and disadvantage of FET with your fertility doctor.
b) Prevention of Ovarian Hyper Stimulation Syndrome (OHSS)
OHSS is a risk that every fertility doctor would like to avoid. Typically it happens in an IVF cycle, among women who have Polycystic Ovarian Syndrome ( PCOS). Women who develop OHSS can become unwell after the egg collection procedure.
If she becomes pregnant in the same cycle, the OHSS can further worsen and increase her risk of complications such as fluid collections in the lung and abdomen. She is also at risk of developing deep vein thrombosis and having a miscarriage.
The best strategy to eliminate or minimise the risk of OHSS is by freezing all the embryo/s. This strategy allows the woman time to recover and the FET can be done at a later date.
c) Ability to transfer embryo at a later date
Couples with a busy work schedule, sometimes have difficulty to take time off work to complete the whole IVF treatment in the same month. FET allows IVF treatment to be completed in two parts. The first part consists of ovarian stimulation, egg harvesting and embryo formation and freezing. The second part of the treatment consists of a FET, which can be done at a time when the couple is ready physically and mentally.
d) Ability to do genetic screening on the embryo (PGS)
To improve pregnancy rate and to reduce miscarriages, embryos can be genetically tested before it is transferred into the womb. This test is called Pre-implantation Genetic Screening ( PGS). PGS allows the doctor to choose a genetically normal embryo to be transferred, thus improving implantation rate ( i.e. pregnancy rate).
Typically, PGS is done when the embryos reach a blastocyst stage (Day 5 or 6 ). The biopsied embryos are frozen while awaiting the results of the PGS. The FET is done a month later with the genetically-tested normal embryo.
e) Controlled progesterone hormone level
In a natural period cycle, an egg is made to ovulate every month in a woman’s ovary.
In an IVF cycle, medications are given to make more eggs to grow ( typically between 8-10 eggs). These high number of eggs leads to a higher level of hormones which are produced by the developing eggs. Higher level of progesterone hormone is known to reduce pregnancy rate. This is because the higher level of progesterone makes the lining of the womb not conducive for embryo implantation.
In a FET cycle, the embryo is transferred after a woman ovulates naturally. This is known as natural cycle FET. In a natural cycle FET, the progesterone level mimics levels which occurs in a natural conception, thus improving pregnancy rate in a natural cycle FET.
f) Ability to do more than one embryo transfer procedure
The freezing and thawing technology allows excess embryos, after the initial embryo transfer procedure, to be frozen safely and to be used later. FET gives a couple multiple embryo transfer opportunities without having to undergo multiple ovarian stimulation and egg collection procedures. This gives couples an opportunity to have a larger family from a single IVF cycle.
g) Overall cost saving
IVF is an expensive treatment. If the first attempt of embryo transfer fails to give the couple a successful pregnancy, they have the ability to prepare for another embryo transfer via FET without the need to undergo a fresh new IVF cycle. Furthermore, FET is considerably cheaper compared to a fresh new cycle of IVF. In addition to financial savings, couples are spared the emotional burden of going through a fresh new IVF cycle.
h) More patient friendly
FET when done in a natural period cycle, is very patient-friendly. Embryo/s is/are transferred three or five days after ovulation. Ovulation can be monitored using commercial ovulation urine test kits that is easy to use. Couples are relaxed as they have less need for medication pre and post FET. The whole journey towards parenthood may mirror a natural pregnancy experience for the couple.