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The first live birth in the world after frozen embryo transfer occurred in 1984. In our country, Prof. Dr. Semra Kahraman and her team tried embryo freezing for the first time in 1994 and achieved the first live birth (twins) in 1995. As a result of developments in IVF treatment, especially embryo culture and freezing process, the number of frozen-thawed embryo transfers has significantly increased. Many studies have reported that frozen-thawed embryo transfers have a higher success rate than fresh transfers.

ENDOMETRIAL PREPARATION FOR FROZEN-THAWED EMBRYO TRANSFER IN NATURAL CYCLE

January 2019

ENDOMETRIAL PREPARATION FOR FROZEN-THAWED EMBRYO TRANSFER IN NATURAL CYCLE

 

The first live birth in the world after frozen embryo transfer occurred in 1984. In our country, Prof. Dr. Semra Kahraman and her team tried embryo freezing for the first time in 1994 and achieved the first live birth (twins) in 1995. As a result of developments in IVF treatment, especially embryo culture and freezing process, the number of frozen-thawed embryo transfers has significantly increased. Many studies have reported that frozen-thawed embryo transfers have a higher success rate than fresh transfers.

According to these studies;

Drugs that we use to obtain eggs in high quantities in fresh cycles cause a supraphysiological estrogen level.

Supraphysiological estrogen level negatively affects the endometrium (uterine lining) and reduces the rate of embryo implantation.

Therefore, the embryos that reached the blastocyst stage in patients with a good ovarian response and that were frozen using the vitrification technique, have been proven to be more successful in another cycle which was prepared without drugs, in a so-called natural cycle.

Embryo freezing process in our center

In our center, embryo freezing process is performed in the following cases:

  • In cases with a risk of ovarian hyperstimulation syndrome (OHSS),

  • With the purpose of a preimplantation genetic diagnosis (PGD),

  • In the presence of good and high quality surplus embryos after fresh transfer,

  • In emergency surgical operations or febrile illnesses that prevent fresh embryo transfer or in cases requiring hormonal treatment.

A successful pregnancy requires a good quality embryo that could reach an advanced stage, a properly prepared endometrium, and good synchronization between embryonic and endometrial development. The endometrium should be prepared properly before the frozen-thawed embryo transfer.

Endometrial preparation is performed in two ways:

  • Natural cycle: The endometrium is naturally prepared by the hormones released by the follicle (egg) that grows in the natural cycle itself without using drugs.

  • Artificial cycle: The endometrium is artificially prepared by exogenous estrogen.

 Our center prefers the natural cycle for frozen embryo transfers.

Advantages of the natural cycle:

  • It is natural, thus does not require drug use.

  • It does not include the risks that may arise due to the use of long-term hormone (estrogen). These risks include hormone-dependent weight gain, the need to take medication every day, the possibility to cause a thromboembolism (formation in a blood vessel of a clot that breaks loose and is carried by the blood stream to plug another vessel) which is life-threatening, and a risk to those with a family history of breast cancer. 

In order to perform a natural cycle in a case, the menstrual cycle should be regular. For example, the time between the the first day of one menstrual cycle to the first day of the next menstrual cycle should not be shorter than 21 days or longer than 35 days. We examine the patient for whom we plan a frozen embryo transfer in the natural cycle by transvaginal ultrasonography (TVUSG) on the second day of her menstrual cycle, and evaluate her ovaries and uterus. After the first examination, we invite the patient again 7 - 8 days later depending on the length of her menstrual cycle and follow the follicle diameter and endometrial thickness. In order to see the LH level, which is an indication of the ovulation time, we have one or two blood samples taken from the patient. When the follicle diameter is 16-20 mm, the endometrial thickness reaches above 7 mm and the LH level rises above a critical threshold level, rhCG is injected to the patient in order to trigger ovulation and to decide the transfer day according to the day on which the embryo was frozen. Since we apply the embryo transfer strategy on the 5th day in our center, we perform embryo transfer 6 days after rhCG injection.






Measurement of endometrial thickness                         Follicle diameter on ovulation day
on the day of ovulation                                                                      






During the freezing process by vitrification, preventive chemicals and complex sugar molecules replace water molecules and protect the cells from the crystallization damage that may occur during freezing process.





During the embryo thawing process, water molecules enter the cell and allow the embryo to regain its volume.




Gönül ÖZER MD.

SAYFA BAŞINA DÖN