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The wikipedia page on surrogacy highlights two main forms of surrogacy: Traditional Surrogacy and Gestational Surrogacy. Traditional surrogacy inseminates the surrogate mother with sperm, while gestational surrogacy uses in vitro fertilization to form an embryo from egg and sperm, which is then transferred into the surrogate mother.

It does not discuss whether surrogacy is possible after a natural fertilization has already taken place, such as if a woman becomes pregnant and then wishes, for whatever reason, to have a surrogate take the baby to term. Is this biologically possible? If it is possible, what is the mechanism? Also, if possible, is heightened risk a major reason it is not more common?

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No, it is not possible. The problem is the fertilization which takes place near the ovary. It takes the new forming blastocyst about 4-5 days to wander through the fallopian tube to reach the uterus and 8-9 days in total to implant itself into the uterine wall. See the picture below (from the Wikipedia article on fertilization):

enter image description here

You would have to get the blastocyst out of the right fallopian tube, make sure it survives the procedure and then implant it into the uterus of a woman which is about in the same phase of their period (otherwise the uterus is not ready to allow implantation). It is already hard enough to do in vitro fertilization where you can control the environment.

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  • $\begingroup$ in other words...have you ever tried to find a fertile zygote in a fallopian tube? the physician would have to be in there with a light and a microscope and some forceps...and its 0.1 mm in diameter! yow that sounds impossible and painful and interminable! $\endgroup$ – shigeta Mar 7 '14 at 22:48
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    $\begingroup$ Thanks for the short version :-) And you would have to choose the right tube as well... $\endgroup$ – Chris Mar 8 '14 at 8:33
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There are different types of surrogacy, but as you said the most common one are traditional and gestational surrogacy.

Traditional surrogacy normally involves intrauterine insemination (IUI), so the eggs of the surrogate are used in the surrogacy process. Once the fertilization takes places it's not possible to extract the embryo.

On the other hand, in gestational surrogacy the creation of the embryos is done via an IVF process, and once they are created they are transferred to the surrogate. So in this process, the fertilization process take place out of the surrogate body.

So, in summary, while gestational surrogacy uses a IVF technique to create an embryo that afterwards is transferred to the surrogate, traditional surrogacy uses IUI to artificially inseminate the gestational carrier. IUI is less complicated than IVF, and this process can be repeated several times until a pregnancy is achieved. However, it's not possible to make the fertilization in one woman and afterwards transfer the embryos to the surrogate, that would be extremely complicated.

Here you can get more info about the different forms of surrogacy.

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  • $\begingroup$ Hi, welcome to the site! I'm honestly not sure what this adds to what has already been said... and in a lot of ways this looks more like a comment than an answer. Sure, it does very briefly answer the question (1 sentence with no backup other than "that would be extremely complicated"), but the rest of the answer is totally incidental to the question posed. In the future, please try to keep answers directed specifically toward the question posed. Thanks! $\endgroup$ – rotaredom Feb 1 at 20:41

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