Embryos are usually frozen on days 1, 3, 5 and 6 after fertilization. We aim to replace the embryos into your uterus at the correct time in relation to ovulation and the thickness of the lining of your uterus (endometrium).
Management of a FER treatment cycle
The frozen embryo replacement cycle is relatively non‐invasive compared to an egg collection cycle. The embryos can be replaced either in a natural cycle or in a controlled cycle depending on whether we can easily monitor the time of natural ovulation. In a controlled cycle a leuprorelin injection and estradiol tablets are administered in order to prepare the endometrium for implantation as an alternative to the natural changes occurring in the endometrium in a spontaneous ovulatory cycle.
To properly monitor the development of your endometrium with ultrasound, we need to do approximately four scans. Your embryos are thawed either when ovulation has occurred (natural cycle), or when the endometrium is thick enough (controlled cycle).
The laboratory will thaw your embryos so that their development corresponds to right time of your cycle. The exact timing will depend upon the stage at which your embryos were frozen.
Thawing your embryos
Before the laboratory can thaw your embryos, both partners must sign the consent form in the presence of one of our medical staff.
Not all embryos survive the freezing, storage and thawing process. On the morning of your embryo transfer, the laboratory will assess your embryos to see if they are suitable for transfer. If they are, the embryo transfer can proceed.
The Embryo Transfer
For this procedure a fine tube (catheter) is passed through the cervix and the embryos are injected high into the uterus in a minute amount of culture medium. This technique does not normally require sedation, and is usually pain‐free. The transfer will be made easier if you have a full bladder when you attend for this procedure.
After the Embryo Transfer
You will have already started pessaries of a hormone called progesterone to support the lining of the uterus and 12 days after your embryo transfer a blood test (ßhCG) is carried out to see if you are pregnant.
The Success rate of FER
The pregnancy rate using frozen/thawed embryos is generally less than when using fresh embryos, however this varies according to a number of factors:
- Previous pregnancy from this group of embryos
- Age of female partner when the eggs were collected
- Quality and number of embryos available to freeze.