In both surrogacy and in vitro fertilization (IVF), it is very common to have questions about the number of embryos to be transferred.
This decision must be made taking into account different aspects such as the embryonic quality or the origin of the gametes among others. However, the high prices of surrogacy and the long-lasting desire to have a baby mean that these people do not care or even want a multiple pregnancy.
Nonetheless, it is important to remember that a twin pregnancy carries a higher risk for both the woman carrying the pregnancy to term and the future babies. For this reason, it will be essential to decide in a rational manner how many embryos should be transferred to the surrogate's uterus.
Provided below is an index with the 8 points we are going to expand on in this article.
Number of embryos to be transferred
Until relatively recently, the trend for most specialists was to transfer two or three embryos. However, it has been seen that transferring a greater number of embryos doesn't translate directly into a possible pregnancy. What is really important is to transfer embryos of good quality, and therefore a single embryo of excellent quality would be sufficient to achieve a gestation.
The change in the number of embryos to be transferred has been due to advances in assisted reproduction techniques. For example, the emergence of incubators with Time-Lapse technology or the optimization of embryo vitrification has been a revolution in the field of fertility. These advances allow for better embryo selection and quality, which increases the rate of implantation and pregnancy.
Therefore, the aspects to be taken into account when selecting the number of embryos to be transferred to the pregnant woman are the following:
- Quality of the embryos. In the case of A-grade embryos, the transfer of a single embryo will be chosen. However, if the embryo is of C or D quality, the transfer of two embryos may be considered.
- Embryonic stage, that is, whether these embryos are on their 3rd or 5th day of development.
- Endometrial receptivity. The endometrium is essential for the embryo to implant in the uterus and it is important that it looks trilaminous and is approximately 8-12 mm thick.
- Origin of the eggs, as well as their quality. The probability of pregnancy will not be the same if the eggs are from a young, healthy donor as if they come from an older patient.
In addition, it is important to take into account the opinion of the pregnant woman, since she will be the one to carry the pregnancy to term.
Risks of Multiple Pregnancy
Any pregnancy has its risks and there can be complications, but in multiple pregnancies the risk is much higher. A pregnancy of two or more babies can pose dangers to the health of both the gestational carrier and the babies.
As it is a surrogacy process, the risk is assumed by the gestational carrier. This woman puts her health and her life at risk to help those who cannot otherwise have children to become parents.
The most common complications in a multiple pregnancy are listed below:
- Distension of the uterus.
- Placenta previa.
- High blood pressure.
- Increased chance of miscarriage.
- Premature birth.
- Low birth weight.
- Post-partum hemorrhages.
It is essential to bear in mind that a multiple pregnancy is much more common in surrogacy than in IVF itself. Therefore, the necessary precautions must be taken to ensure the health of the gestational carrier and the baby.
Single embryo transfer
Gestational carriers in surrogacy treatment are healthy, young women who have gone through natural, uncomplicated pregnancies. In addition, these women have undergone numerous medical and psychological tests to ensure that they are fit to carry a pregnancy to term, without any risk to themselves.
Therefore, they are women who do not have any fertility problems that make implantation difficult or interfere with the normal progress of the pregnancy. So why transfer more than one embryo?
Good quality embryos have a high potential for implantation, so that, together with good endometrial receptivity of the gestational carrier, they are most likely to implant and result in a pregnancy.
Also, in cases of men who resort to surrogacy to become parents without a female partner and in cases where the intended mother cannot provide her own eggs, donor eggs are used, which greatly increases the chances of pregnancy.
Since in cases of good embryonic quality the probability of multiple pregnancy in surrogacy is very high, a single embryo should be transferred.
When to transfer more than one embryo
More than one embryo should only be transferred in specific cases such as the following:
- Low gamete quality.
- Low embryonic quality.
- Previous IVF failures in the surrogacy process.
If the doctor recommends the transfer of more than one embryo, two embryos may be transferred. The greater the number of embryos transferred, the greater the risk of multiple pregnancy.
We must not forget that by not being the intentional mother who is going to gestate, another woman's health is being put at risk. This woman has a home, a spouse, and children, and she puts her life in the hands of her parents with the intention of helping them to fulfill their deepest desire. It is therefore essential to avoid taking unnecessary risks and to ensure the safety of the woman who will be caring for the baby during the first months of her life.
FAQs from users
Is there a difference in the endometrial preparation if one or two embryos are transferred?
No, the number of embryos to be transferred does not influence the preparation of the endometrium. This phase of the process will be the same, that is, the woman who will carry the pregnancy to term will have to administer estrogen and progesterone so that the endometrium acquires the ideal characteristics that favor embryo implantation.
The greater the number of embryos transferred, the higher the pregnancy rate?
In principle yes, but it is also important to know the quality of the embryos transferred. For example, if an embryo of quality A is transferred, there will be a greater possibility of pregnancy than if two embryos of worse quality of grade D are transferred.
Therefore, it will be necessary to evaluate different aspects such as the quality of the embryos, the origin of the eggs, the endometrial receptivity, etc. in order to decide on the number of embryos to be transferred in order to have a high guarantee of success.
Does the quality of the gametes influence the decision on the number of embryos to be transferred?
The answer is yes. If the gametes (eggs and sperm) are of poor quality, it is most likely that the embryos generated in the laboratory would be of low quality. Therefore, these embryos may even present chromosomal alterations that would pose a risk of failure of the fertility treatment.
On the other hand, if donated gametes are used, the quality of the embryos will be higher and, therefore, the possibilities of pregnancy will increase.
What does the transfer of one or two embryos depend on?
The decision to transfer one or two embryos should be made by studying different factors and taking into account the medical recommendation. Among these, it will be important to analyze the quality of the embryos, the origin of the eggs, the receptivity of the endometrium and whether previous cycles of IVF have been carried out without success.
The purpose of all of this is to increase the possibility of pregnancy, but to avoid a multiple pregnancy at all times.
Suggested for you
We have commented that the woman who is going to carry the pregnancy to term in a surrogacy process must previously pass multiple medical tests. We recommend you visit this link to read more in-depth information about it: Medical tests for the surrogate before and during pregnancy.
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Cattoli, M. and Borini, A. (1996) The ideal number of transferred embryos: a retrospective analysis. [Abstr. no. 187] Hum. Reprod., 11 (Abstr. Book 1), 88.
Englert, Y., Devreker, F., Bertrand, E. et al. (1993) Double instead triple embryo transfer as a prevention of multiple pregnancy. [Abstr. no. 18] Hum. Reprod., 8 (Abstr. Book 1), 13.
Forman EJ, Hong KH, Ferry KM, Tao X, Taylor D, Levy B, et al. In vitro fertilization with single euploid blastocyst transfer: a randomized controlled trial. Fertil Steril 2013;100:100–7.e1.
McLernon DJ, Harrild K, Bergh C, Davies MJ, de Neubourg D, Dumoulin JC, Gerris J, Kremer JA, Martikainen H, Mol BW, Norman RJ, Thurin-Kjellberg A, Tiitinen A, van Montfoort AP, van Peperstraten AM, Van Royen E, Bhattacharya S: Clinical effectiveness of elective single versus double embryo transfer: meta-analysis of individual patient data from randomized trials. BMJ 2010, 341:6945.
Montag M, Toth B, Strowitzki T. (2013). New approaches to embryo selection. Reprod Biomed Online;27:539–46.
Pandian Z, Marjoribanks J, Ozturk O, Serour G, Bhattacharya S: Number of embryos for transfer following in vitro fertilisation or intra-cytoplasmic sperm injection. Cochrane Database Syst Rev 2013, 7:CD003416.
Practice Committee of American Society for Reproductive Medicine; Practice Committee of Society for Assisted Reproductive Technology: Criteria for number of embryos to transfer: a committee opinion. Fertil Steril 2013, 99:44–46
Practice Committee of the Society for Assisted Reproductive Technology and Practice Committee of the American Society for Reproductive Medicine: Elective single-embryo transfer. Fertil Steril 2012, 97:835–842.
Roseboom, T.J., Vermeden, J.P.W., Schoute, E. et al. (1995) The probability of pregnancy after embryo transfer. Hum. Reprod., 10, 3035-3041.
Tomás C, Tikkinen K, Tuomivaara L, Tapanainen JS, Martikainen H. (2002). The degree of difficulty of embryo transfer is an independent factor for predicting pregnancy. Hum Reprod; 17:2632–5.
Vilska S, Tiitinen A, Hyden-Granskog C, Hovatta O. Elective transfer of one embryo results in an acceptable pregnancy rate and eliminates the risk of multiple births. Hum Reprod 1999;14:2392– 2395
William B. Schoolcraft, M.D., for the ASRM American Society for Reproductive Medicine (April 2016). Importance of embryo transfer technique in maximizing assisted reproductive outcomes. Vol. 105, No. 4. Colorado Center for Reproductive Medicine, Lone Tree, Colorado
FAQs from users: 'Is there a difference in the endometrial preparation if one or two embryos are transferred?', 'The greater the number of embryos transferred, the higher the pregnancy rate?', 'Does the quality of the gametes influence the decision on the number of embryos to be transferred?' and 'What does the transfer of one or two embryos depend on?'.
I’m glad that most clinics opt now for a single embryo transfer as it guarantees the safety of the surrogate and the baby.