Beyond DNA: The Biology of Connection in Donor-Egg Pregnancy
For some women considering or using donor eggs, one question can feel particularly important: If my baby doesn't have my genes, is there still a biological connection between us?
The truth is, the answer is utterly fascinating. A baby conceived using a donor egg inherits the DNA contained in that egg from the egg donor, together with DNA from the sperm provider. Carrying the pregnancy does not change who provided those inherited genes. But genetics is only one part of human biology.
Pregnancy is an extraordinarily interactive biological process. From implantation onwards, the developing baby, placenta and pregnant woman's body communicate continuously. The mother's immune, hormonal, metabolic and uterine environments participate in the baby's development. Cells travel in both directions across the placenta, with some potentially remaining in mother and child for decades.
Two areas of research: epigenetics and microchimerism, are helping us understand just how biologically interconnected pregnancy really is.
Genetics and epigenetics are not the same thing
Firstly, we must distinguish the difference between genetics and epigenetics. Our genes are sections of DNA containing biological instructions. Epigenetic processes help regulate those instructions, for example, influencing whether particular genes are more or less active at particular times. A useful analogy might be to think of DNA providing part of the biological "text", while epigenetic mechanisms help determine which sections are read and how they are used.
In a donor-egg pregnancy, the recipient mother can’t replace or contribute to the DNA inherited from the egg donor. However, the embryo does not develop independently of the woman carrying it. The uterine environment, placenta, maternal hormones, nutrition, metabolism, immune signalling and many other aspects of pregnancy form part of the developmental environment in which the fetal genome operates.
Research examining pregnancies conceived using donor eggs is particularly interesting because the genetic contribution of the egg can be distinguished from the environment provided by the woman carrying the pregnancy. Studies have found differences in placental DNA methylation, one important epigenetic mechanism, in pregnancies conceived using assisted reproductive technologies, including egg donation. Recent research has also identified altered methylation and expression of genes involved in placental blood-vessel development in egg-donation pregnancies. (PubMed Central (PMC))
Exactly what produces these differences is complicated. The donor egg itself, laboratory procedures involved in IVF, embryo freezing and transfer, the recipient's uterine environment and interactions between these factors may all contribute. Researchers cannot simply attribute an epigenetic difference found in a donor-egg pregnancy to the woman carrying the pregnancy. (PubMed Central (PMC)). Nevertheless, the broader principle has been well established: genes operate within an environment, and pregnancy provides a profoundly important developmental environment.
It is misleading to describe a woman carrying a donor-egg pregnancy as simply an "incubator". Her body is actively involved in supporting and regulating fetal development throughout pregnancy.
The placenta creates a biological conversation
The placenta makes this relationship even more remarkable. Most of the placenta originates from the embryo. In a donor-egg pregnancy, it therefore carries genetic material derived from the egg donor and sperm provider. Yet this genetically distinct placenta embeds itself within the recipient mother's uterus and interacts continuously with her circulation and immune system.
Egg-donation pregnancies provide researchers with an unusual model for studying this relationship because the fetus may be genetically unrelated to the woman carrying it. Research has demonstrated substantial maternal immune adaptation in these pregnancies: despite the greater genetic difference between fetus and mother, pregnancy can still establish the immune tolerance necessary for the fetus to develop. (PubMed). For nine months, the mother, placenta and fetus participate in continuous biological communication, and that communication is not limited to hormones and molecular signals. They also exchange cells.
Your baby's cells may remain in your body
During pregnancy, small numbers of fetal cells cross the placenta and enter the mother's circulation. At the same time, maternal cells travel in the opposite direction and enter the fetus. This phenomenon is known as fetomaternal microchimerism.
The word chimera may sound rather dramatic. In biology, however, it simply describes an organism containing a small population of cells that are genetically different from most of its own cells. The phenomenon is a normal feature of human pregnancy. (ScienceDirect) What is particularly fascinating is what happens afterwards.
Some fetal cells do not disappear when pregnancy ends. They can persist in the mother's body for decades and have been identified in maternal blood, bone marrow and numerous tissues and organs. (PubMed Central (PMC))
The exchange works in the other direction too. Cells originating from the woman carrying the pregnancy can remain within her child. Research increasingly suggests that maternal microchimeric cells can persist within offspring, including within the central nervous system. (PubMed Central (PMC))
This process does not depend upon the mother having provided the egg. Microchimerism is produced through pregnancy and placental exchange. It is therefore also relevant to donor-egg pregnancies. Research specifically examining egg donation has highlighted this exchange between a genetically distinct fetus and the woman carrying the pregnancy. (PubMed)
Put simply, a mother may carry some cells originating from the child she carried, while that child may carry a very small number of cells originating from her. This does not make them genetically related in the conventional sense. The child's inherited genome still came from the egg and sperm providers, but does represent a different form of biological connection.
Could this cellular exchange contribute to attachment?
This is where the science becomes fascinating, but also where we need to be particularly careful not to claim more than researchers have established. Fetal microchimeric cells have been detected in the maternal brain. A recent review found evidence that these cells can cross the blood–brain barrier, persist within brain tissue and, particularly in experimental research, display characteristics of neural and glial cells. Researchers are investigating whether they could participate in processes including immune regulation, tissue repair and neuroplasticity. However, their precise function remains unresolved. (Wiley Online Library)
Researchers have also proposed an intriguing evolutionary theory: a baby's survival depends heavily upon maternal investment after birth. Systems controlling lactation, caregiving and maternal behaviour are therefore extremely important to infant survival.
Fetal microchimeric cells have been found in tissues relevant to these processes, including the breast, thyroid and brain. Researchers Boddy and colleagues proposed that fetal cells might potentially influence maternal physiology in ways that support continued investment in the baby, for example through lactation or biological systems associated with maternal behaviour and attachment. (PubMed Central (PMC))
It has not, however, been demonstrated that fetal cells cause a mother to bond with her baby. We currently do not have evidence showing that women with more fetal microchimeric cells are more attached to their babies, or that microchimerism explains psychological attachment between mothers and children.
The research allows us to say that cells from a baby can enter and persist in the mother's brain and other tissues, and that scientists are investigating what those cells might do. It does not allow us to say, "Your baby's cells in your brain make you love your baby."
Pregnancy itself may still contribute to the developing relationship
Attachment is much bigger than either genetics or microchimerism. The psychological relationship between parent and baby develops through many interacting processes: expectations about the baby, experiences during pregnancy, fetal movement, birth, caregiving, touch, smell, eye contact, responding to distress, feeding, sleep, repeated interactions and simply spending time together.
There are also major hormonal and neurological adaptations associated with pregnancy and becoming a parent. So there is no reason to expect the absence of a genetic relationship to prevent attachment. Nor does attachment necessarily arrive instantly at birth. Some parents experience an immediate sense of connection; others develop it gradually through caring for and getting to know their baby. Both experiences occur in families formed with and without donor conception.
What does all of this mean if you are using a donor egg?
Perhaps the most important message is that we do not need to blur the distinction between genetic connection, gestational connection and relational connection in order forall three to matter.
The egg donor makes an important genetic contribution to the child. Acknowledging the biology of pregnancy should never require minimising that contribution. Equally, acknowledging the donor's genetic contribution does not mean describing the woman who carries the pregnancy as biologically irrelevant.
Her body sustains the pregnancy. Her uterus and the developing placenta interact continuously. Her immune and endocrine systems adapt to the developing fetus. The intrauterine environment participates in fetal development and gene regulation. Cells pass between her and the baby, and some may remain in each of their bodies for many years. There is a genuine biological relationship created through pregnancy, even when there is no genetic relationship through the egg, but we can’t currently tell how much any particular biological mechanism contributes to the emotional bond between a mother and her child.
The evidence already gives us a much richer picture than the idea that either you "share DNA" or you have no biological connection at all.
Genetic inheritance is one kind of biological connection. Pregnancy creates others. And attachment develops through an even broader combination of biology, experience, caregiving and relationship.
References and further reading
Abey, N.O. (2026). Feto–maternal microchimerism and the brain: Mechanisms, neurological implications, and translational perspectives. American Journal of Reproductive Immunology, 96(3), e70317. (Wiley Online Library)
Boddy, A.M., Fortunato, A., Wilson Sayres, M. & Aktipis, A. (2015). Fetal microchimerismand maternal health: A review and evolutionary analysis of cooperation and conflict beyond the womb. BioEssays, 37, 1106–1118. (PubMed Central (PMC))
Gammill, H.S. & Harrington, W.E. (2017). Microchimerism: Defining and redefining the prepregnancy context – A review. Placenta, 60, 130–133. (PubMed Central (PMC))
van der Hoorn, M.L.P. et al. (2010). Clinical and immunologic aspects of egg donation pregnancies: A systematic review. Human Reproduction Update. (PubMed)
Feto-maternal microchimerism: Memories from pregnancy (2022). iScience, 25(1), 103664. (ScienceDirect)
Differential Effects of Assisted Reproduction Technology on Placental Epigenetics and Angiogenesis: Insights from Fresh, Frozen, and Egg Donation Pregnancies (2025). (PubMed Central (PMC))