Which one is better? Fresh embryo transfers or frozen embryo transfers (FET)?
One of the steps of In Vitro Fertilization (IVF) Process is the embryo transfer. Embryos are results of fertilization of the female egg cell by the male sperm cell.
Embryos can be either “fresh” (fertilized egg cells of the same menstrual cycle) or “frozen” (fertilized egg cells that have been generated in a preceding menstrual cycle and have undergone embryo cryopreservation). Frozen embryos will be thawed before embryo transfer procedure. Hence, this procedure is called “frozen embryo transfer” (FET).
According to CDC (Centers for Disease Control and Prevention) 2014 Assisted Reproductive Technology (ART) National Summary Report, the percentage of transfers resulting in pregnancies (%) of frozen embryos from non-donor eggs are higher than fresh embryos from non-donor eggs.
|Type of Cycle||Age of the Woman|
|Fresh Embryos from non-donor eggs|
|Percentage of transfers resulting in pregnancies (%)||54.6||48.1||38.6||26.5||16.0||6.7|
|Frozen Embryos from non-donor eggs|
|Percentage of transfers resulting in pregnancies (%)||56.6||54.1||49.7||44.7||34.4||22.9|
If you look at the percentage of transfers resulting in pregnancies across the woman’s age categories, you will see the number increases as the woman gets older. For woman younger than 35, there is not much difference in the pregnancy success rate.
Why frozen embryo transfers resulted in pregnancies higher than the fresh embryo transfers?
- Increased implantation rate: Frozen embryo transfer is considered more “natural” hormone environment in the uterus since the woman had to wait a significant amount of time until the hormone levels in the body return to normal. In a fresh embryo transfer, there is a chance that the woman is over stimulated because of the fertility medications prior to the transfer. This unnatural high levels of reproductive hormones estrogen and progesterone could deter the effectiveness of embryo implantation.
- Decreased miscarriage rates, increased pregnancy rates, decreased pregnancy with multiple risks: Some IVF programs are very strict about the quality of the embryos that will freeze, some are not very strict and will just freeze any remaining embryos. If they are very strict, they may do a screening process called Comprehensive Chromosome Screening (CCS) that analyze the 23 chromosome pairs of the remaining embryos. Approximately 60% of early miscarriages are associated with chromosomal abnormalities. With this Comprehensive Chromosome Screening, they will be able to determine which embryos are normal and eligible for delayed transfer (frozen embryo transfer). Therefore, transferring a single healthy embryo increases pregnancy rates, decreases miscarriage rates, as well as decreases pregnancy with multiples.
For more than 10 years or so, embryo freezing and thawing process have been improved dramatically with the use of vitrification (ultra-rapid freezing) vs. the older slow freezing method. Pregnancy success rates with frozen embryos have been increasing compared to the past. Therefore, frozen embryo transfers actually gives higher success rates than fresh transfers.
If you are a woman younger than 35 years old, the success rate is almost the same if you go with fresh embryo transfer instead of the frozen embryo transfer. But, if you are 35 years old and older, the success rate increases as you get older when you do a frozen embryo transfer compared to a fresh embryo transfer.
Cost of fresh embryo transfer vs frozen embryo transfer
Typically, a frozen embryo transfer is much cheaper than fresh embryo transfer because fertility medication, egg retrieval, embryo culture have been done in a previous cycle. This applies only if you have enough embryos to freeze in the previous cycle. If not, you have to do another round of fertility medication, egg retrieval, and embryo culture which means another cost of a fresh IVF cycle.