According to a study conducted by the Infertility Foundation Institute of Valencia (FIVI), the hypothesis that gestational carriers are capable of modifying the genetic expression of the embryo even when the egg comes from another woman is confirmed.

A little bit of history

In 1990, the British epidemiologist David Baker said that “what happens in the mother’s womb is more important than what happens after birth”. The scientist stated that the placenta and the endometrium of the pregnant woman communicate with each other and are capable of reprogramming the genetics within the framework of Assisted Reproduction treatments that include egg donation and surrogacy. 

This is something that was already suspected not only because of the coincidence between some physical traits between pregnant mothers and babies, but also because of the incidence of certain diseases in children that were related to maternal pathologies during pregnancy. One of the earliest examples of this became evident in children who developed diabetes due to factors related to maternal malnutrition. That is because of a correlation that occurs through epigenetic adaptation, in which a fetus that develops in a context of scarce resources increases its capacity to store more sugar in its body for its own benefit.

However, it was not until 2015 that researcher Felipe Vilella from the FIVI confirmed the existence of this “communication” between the endometrium and the embryo. It was found that the habits of a woman during pregnancy are determinant in embryonic development to the point that they are capable of modifying the expression of the embryo’s genome. Furthermore, it is now known that such epigenetic “communication” occurs even before the embryo implants itself into the endometrium.  

What exactly is epigenetics?

Genetics and epigenetics, although related, are very different things. To begin with, genetics is the biological inheritance of an organism, i.e. the characteristics that parents pass on to their children. On the other hand, epigenetics is the process by which the readability or expression of genes is modified without a change in the DNA code. This means that there are small chemical labels that are added to or removed from our DNA depending on changes in the environment in which we live. These tags play the role of turning genes on or off so that they adapt to the conditions around us without necessarily changing our genome.

If all this terminology is confusing for you, don’t worry, just imagine that genetics are like a dictionary where you will find all the words that make up the organism, from A to Z, and it encompasses all the information contained in your genes. On the other hand, epigenetics is like highlighting some of the words in that dictionary. Of course, all the words will still be contained in it, but there is now a particular focus on some of them. So, the “words” are the genetic information contained in the egg and sperm of the biological parents, the “highlighted words” are what will determine certain aspects of the baby, and the task of the pregnant mother’s womb will be just to “highlight” the “words” that are most relevant to the development of the embryo in that particular womb.

Although this is still a scientific field with much ground to cover, it increasingly seems to show that there are factors which, without being completely linked to genetic elements, can intervene in the cellular environment and determine changes in the stages of development of an organism, from the fertilization of the zygote at the time of conception to its adult form. This helps us realize the extent to which it is the environment that will determine which genes (which remain unaltered) are ultimately expressed and in what forms, something that is essential in determining the very shape of our existence.

What are the causes of these changes?

Epigenetic regulation can be caused by changes in the configuration of chromatin, which is a substance found in the cell nucleus that forms the chromosomal material composed of DNA that is bound to proteins. Its interaction with the basic cellular proteins, which are called histones, is what ultimately causes these changes. This means that if the chromatin is highly condensed, the gene cannot be transcribed, since the elements that help in this transcription cannot access this region of the DNA. Following the same logic, if the chromatin is not condensed, it is possible that there is a transcription of the gene.

There is also the influence of DNA methylation processes, which are responsible for changes in the activity of DNA segments without needing to change their sequence. Their impacts range from genomic imprinting, which selects the genes that will be expressed in us, to inactivation of the X chromosome and the repression of the expression of some transposable genetic elements, ageing and carcinogenesis.

What is its role in assisted reproduction?

Today, we know that our environment has a powerful influence on how our genetic code is expressed. Furthermore, our experiences can also mark our genetic material in ways that we do not yet fully understand. For this reason, it is only logical to think that such marks will be transmitted to our genetic children through surrogacy, which is why it is extremely important to be aware in advance not only of the surrogate mother’s medical history, but also to take the time to learn a little about her personal life. 

Scientific studies seem to indicate that a molecule of endometrial fluid is capable of reprogramming the embryo’s genetics, thus modifying the expression of its genes. This implies that the gestational carrier, even without transmitting her own genetic load, is able to modify it, including if the egg comes from a donor.

During pregnancy, epigenetics not only has the essential role of establishing, from among the 20,000 to 25,000 genes present, which genes will be expressed, but also at what stage of development. This happens inside the pregnant mother’s womb, where there is a set of molecules that are placed around the DNA chains and that will determine whether the genes will be activated or silenced.

Even if this is a lifelong process, it is of particular importance during embryonic and fetal development. When the zygote is formed after fertilization, epigenetic reprogramming occurs, which means that the epigenetics of the parents disappear to avoid the possible accumulation and transmission of errors. It is through this process that a new epigenome is formed.

Thus, it is inside the uterus that the embryo, thanks to the maternal fluids, obtains elements that will bind to its genes and intervene in their expression while affecting the embryonic development. Basically, the gestational carrier modifies the expression of the child’s genetic information.

Keep in mind that finding and choosing a candidate that meets certain requirements is a lengthy but necessary process since it is the first environment in which the baby will live. Be aware that your choice in terms of gestational carrier may eventually result in the emergence of different phenotypes (or physical characteristics) and even influence the cell lineage that will last for generations to come.

As with any pregnancy, particular attention should also be paid to the diet, exercise, stress, consumption of toxic substances (alcohol, tobacco, drugs, etc.) of the gestational carrier, as these factors will definitely influence the baby’s epigenome. Don’t forget that being the first environment in which the embryo develops, it is only logical that it will adapt to the nutrients and molecules that the surrogate mother provides. The intrauterine environment is fundamental for the good development of the embryo to the point of affecting the baby both physically and psychologically for the rest of its life. Take your time, meet several candidates, carefully review their medical history and lifestyle habits, make an informed decision and get proper medical advice because, as you are now learning, the pregnant mother is contributing even more to your child’s future than you first thought.