The term frozen embryo transfer (FET) refers to the treatment cycles that are carried out when we already have the embryos cryopreserved and we just focus on preparing the endometrial lining.
One of the main pre-requisites in proceeding to a frozen embryo transfer is that the uterine cavity has been assessed and there are no abnormalities that distort the endometrial architecture (for example the presence of polyps or fibroids protruding within the cavity). Nowadays, there is no need for invasive testing like a hysteroscopy, HSG or a Saline infusion Sonohysterogram, as we can have a clear view of the endometrial cavity with a 3D/4D transvaginal ultrasound scan performed mid-cycle. Obviously, if an abnormality is discovered, then this should be corrected surgically before proceeding with a frozen embryo transfer.
Methods to perform
A frozen embryo transfer may be performed in two ways:
- Using a single injection to suppress the ovarian function and then administer estrogen tablets to prepare the endometrial lining. In many cases the injection can be omitted. The estrogen supplementation phase takes approximately 15-20 days. Monitoring scans of the lining are required during this period of time.
- During a natural menstrual cycle, estrogen is produced by the developing follicle. This estrogen acts on the uterus to thicken and mature the uterine lining. However, natural FET cycles are hard to schedule and may carry a risk of cancellation and hence why we are reluctant to offer these for patients coming from abroad.
Once the endometrial thickness and morphology has reached the required criteria, we start the use of progesterone vaginal preparations or injectable progesterone and schedule the embryo transfer. On the day of embryo transfer, embryos are thawed out. Nowadays, here at Newlife IVF Greece we have an over 98% survival rate with the new methods used to cryopreserve embryos (vitrification).
At Newlife IVF Greece we generally freeze embryos at the blastocyst stage, in order to have the maximum information possible regarding the embryo quality. This makes our assessment more accurate and improves pregnancy rates.
Pregnancy rates using frozen embryos
Recent scientific data suggest that there is no difference in pregnancy rates between fresh and frozen embryo transfers. There is also evidence that in some cases of own egg treatment we might get better results with a frozen embryo transfer. This is because the hormones produced by the multiple follicles developed from ovarian stimulation might have a detrimental effect on the uterine receptivity.
Length of storage
In theory embryos can be stored indefinitely as they are not influenced by the length of freezing. Indeed women who have been successful in achieving a pregnancy through IVF, have excellent chances of conceiving again in the future following treatment with the use of their frozen embryos from the initial stimulation cycle.
A recent study reported at the European Society for Human Reproduction and Embryology (ESHRE) reported that there was no difference in the rate of birth defects whether the children came from frozen embryos or fresh embryos.
Chrysa Karakosta, BSc, MSc
Chrysa is the Lab co-Director at Newlife IVF Greece, in Thessaloniki Greece, from the beginning of 2010 and now heads the International Patient Department.