Frozen Embryo Transfer
During hormone stimulation in an IVF cycle several oocytes (egg cells) develop. These oocytes will be fertilized in our lab, which will most often result in the formation of several high quality embryos (fertilized egg cells). One of these embryos will be transferred into the uterus after fertilization; this is called “fresh embryo transfer” (Fresh-ET). The rest of the embryos will be frozen (cryopreserved) individually for later use. These cryopreserved “spare” embryos may later be thawed and used in subsequent embryo transfers (Frozen ETs). The chance of getting pregnant during a Frozen-ET is similar to during a Fresh-ET.
If several embryos develop some will be cryopreserved (frozen) for future use.
The process of frozen embryo transfer (Frozen-ET) is much shorter than IVF and requires fewer appointments and far less medication than your IVF treatment. Before implanting the embryo the uterine endometrium (inner lining) has to be thickened and prepared to receive the embryo. There are two ways to achieve the endometrial thickening before Frozen-ET; stimulated cycle Frozen-ET or natural cycle Frozen-ET. In the stimulated Frozen-ET, the uterine endometrium is stimulated by a pre-treatment with the hormones estrogen and progesterone, to mimic the first part of the menstrual cycle. In natural cycle Frozen-ET, we monitor the natural menstrual cycle with ultrasound and blood tests to determine the ideal time for embryo transfer. At Stockholm IVF we prefer to use natural cycle embryo transfers unless the patient has a condition that requires premedication, such as highly irregular or absent menstrual cycles.
The embryo transfer works much in the same way as a in normal IVF. The embryo may either be transferred at its 8-cell stage or, as a more developed blastocyst. The physician transfers the embryo using a fine, ultrasound-guided catheter inserted with the tip inside the uterus via the cervical canal. Embryo transfer is not painful and generally does not require any sedating or painkilling premedication. After transfer, the embryo is well protected within the uterus and you can return to daily activities right after the procedure.
Embryo or blastocyst transfer into the uterus does not guarantee pregnancy. The endometrium in the uterus has to accept the embryo during implantation and a placenta that will nurture the growing foetus has to develop. To increase the chances for healthy development you will be prescribed vaginal suppository pills of progesterone, which is a naturally occurring female sex hormone produced by the ovaries. Its most important function is to stimulate the uterine endometrium to accept an embryo. Missing your predicted menstrual period within 3 weeks after oocyte retrieval is usually the first sign of successful IVF-treatment. Pregnancy can be confirmed with a urine pregnancy test, and if this turns out to indicate pregnancy we perform a follow-up ultrasound examination to make sure your baby is growing normally at the correct position inside the uterus. All subsequent visits during your pregnancy will be taken care of by the antenatal care service, just as with a normal pregnancy.