In order to fertilize the Surrogate Mother, it is necessary that healthy embryos would be present in an appropriately primed uterus. In case of normal reproduction and during the standard In Vitro Fertilization procedure, embryos and endometrium are automatically in synchrony by virtue of the endocrine changes over the course of the natural stimulated cycle. However, for the couples of the Intended Parents, who prefer gestational surrogacy agreement, the source of eggs becomes different from the Surrogate Mother’s uterus. And this makes synchrony between the two women: the Intended Mother and the Surrogate Mother, each of whom has her own menstrual cycle, quite a problem. It is extremely unlikely, moreover, it is practically impossible that the egg retrieval procedure, which an egg donor is to undergo and the ovulation in the Surrogate Mother occur on the same day, therefore this coincidence is just what is necessary to achieve this synchrony.
Therefore, it is possible to have this synchrony between embryo stage and endometrial stage achieved with the help of taking control of eon of either the “embryo” or the “uterus”. It is possible to accomplish control of the embryos with the help of “freezing” procedure, which is called “cryopreservaton”. As for the endometrium control, it can be accomplished with the help of some hormone replacement. Talking about practice, this has typically meant that either:
1. fresh embryos get replaced in hormone replaced cycles, or
2. frozen embryos get replaced in natural cycles.
Any of the abovementioned methods has proved to be highly effective. Therefore, it is not yet dear whether any of them can be considered as being a superior one.
Here are some of the factors, which can influence the success of these different methods.
Fresh Embryos into the Uterus after Taking Hormones Approach
On average people prefer fresh embryos to be more likely to implant, rather then frozen ones, simply because the embryos, which have not been cryopreserved, have not been subjected to the stress of this “freezing procedure”.
Therefore, in case if fresh embryos are implanted into the uterus of a Surrogate Mother, which was prepared with the help of medications, this may not necessary lead up to an appropriately prepared endometrium. There are numbers of methods of hormone replacement, possible to be employed, and most of them are considered as capable of working. In accordance with early work on this approach, more than 90 % of the time the endometrium appeared appropriate (by biopsy) and ready for the embryo replacement. Subsequent work has also confirmed, that the duration of estrogen replacement varies from as little as 7 days and up to as many as 28 days with little, if any at all effect on the receptivity of the uterus to embryo implantation procedure.
However, it is necessary to point out, that an appropriate uterine lining does not develop in every person, which is treated in this way. That is why it is important for couples, applying this method, to make sure that there is an appropriate response by having a vaginal ultrasound investigation performed in about 2 weeks after the estrogen replacement was performed. It is necessary to keep in mind that the thickness of endometrium at this period of time is to be not thinner than 7 mm, because in case if it is thinner, then the development is most likely to be inadequate and no transfer should be performed up until adjustments, which thicken the endometrium up are made.
Therefore, this method has also its advantages, one of which is that fresh embryos are possible to be transferred into an adequately primed uterus.
To possible disadvantages of fresh embryos replacement method may be referred the following ones:
1. the cost of medications;
2. the lack of certainty about when the transfer should better be conducted, because everything depends on the ovarian response of the egg source;
3. high possibility of inadequate endometrial development;
4. the necessity for all participants to be available at the same time;
5. The necessity of a Surrogate Mother to take supplemental estrogen and progesterone through the first several months of pregnancy, because her own ovaries are not producing these hormones.
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