For many intended parents, one of the first questions about surrogacy is whether the baby will share DNA or blood with the surrogate. It’s natural to wonder about this, since pregnancy creates such a close physical connection between a surrogate and the baby she carries. The truth is simple: in gestational surrogacy, the standard type used almost everywhere in the U.S., the baby does not share DNA or blood with the surrogate.
In this guide, we’ll explain how genetics work in surrogacy, why the surrogate’s and baby’s blood don’t mix, the role of the surrogate’s body in supporting the pregnancy, how epigenetics come into play, what surrogates can and cannot pass on to the baby, and why the U.S. relies almost exclusively on gestational surrogacy today.
How Genetics Work in Surrogacy
DNA Inheritance Comes Only from Egg and Sperm
A baby’s DNA is established at conception when the egg and sperm combine. Half of the genetic material comes from the egg, and the other half comes from the sperm. This genetic code determines inherited characteristics such as eye color, hair type, height potential, and many health-related traits. Once this blueprint is formed, it does not change based on who carries the pregnancy.
In the context of surrogacy, this means the surrogate mother does not add her DNA to the baby. The embryo is created in a fertility clinic through in vitro fertilization (IVF), using the intended parents’ or donors’ genetic material. After the embryo transfer, the surrogate’s body nurtures the pregnancy, but the genetic information remains fixed. Her role is to provide the environment where the baby can grow safely, not to contribute to the child’s genetic makeup.
This distinction is essential for intended parents. Even though the surrogate is physically connected to the baby throughout pregnancy, the baby’s DNA remains entirely tied to the egg and sperm providers.
Gestational Surrogacy: No Genetic Connection to the Surrogate
Gestational surrogacy is the standard practice in the United States and accounts for the overwhelming majority of surrogacy journeys today. In this process, the surrogate carries an embryo created from the intended parents’ or donors’ egg and sperm. She does not provide her own egg. As a result, she has no genetic relationship to the baby.
This type of surrogacy offers clear boundaries. The intended parents are the sole genetic contributors, and the surrogate serves as the gestational carrier. This makes it easier legally and emotionally because there is no overlap between the surrogate’s role as the carrier and the intended parents’ role as the genetic parents. Courts also recognize this separation, which is why legal agreements and pre-birth orders align with gestational surrogacy.
For intended parents, this assurance provides peace of mind. They can be confident that the baby’s DNA, appearance, and inherited traits all come from their chosen egg and sperm, not from the surrogate.
Traditional Surrogacy: The Rare Case Where DNA Is Shared
Traditional surrogacy is very different because the surrogate uses her own egg to conceive, often through artificial insemination. This makes her both the genetic and the birth mother of the child. In this case, the baby does inherit DNA from the surrogate, which can include physical traits or genetic conditions.
While traditional surrogacy played a larger role historically, it is now rarely used in the U.S. This is because it introduces significant legal and emotional challenges. For example, the surrogate could be considered a biological parent under the law, which complicates custody arrangements. It may also create emotional difficulties for the surrogate herself, as she is genetically connected to the child she carries.
Most surrogacy agencies and clinics now avoid traditional surrogacy altogether. Instead, they rely on gestational surrogacy, which removes genetic ties between the surrogate and the baby and provides greater clarity for all parties involved
Why the Surrogate’s and Baby’s Blood Don’t Mix
The Placenta as a Protective Barrier
The placenta is one of the most remarkable organs created during pregnancy. It forms shortly after the embryo implants in the surrogate’s uterus and acts as the lifeline between her body and the developing baby. Through the umbilical cord, the placenta delivers oxygen, nutrients, and hormones to the baby and removes carbon dioxide and waste. This exchange is constant and vital to the baby’s survival.
Even with this close connection, the surrogate’s blood and the baby’s blood remain completely separate. The placenta contains layers of cells that serve as a natural barrier. These layers allow molecules like oxygen and glucose to pass through, but they prevent the actual mixing of blood cells. This design is crucial, as direct mixing could cause the baby’s immune system to react to foreign blood cells or lead to serious complications.
This separation also explains why the surrogate does not “share blood” with the baby. She sustains the pregnancy through controlled transfer of nutrients, but the circulations remain distinct. The placenta is therefore both a gateway and a shield, providing everything the baby needs while keeping the surrogate’s blood cells apart from the baby’s.
The Baby’s Blood Type Comes from the Genetic Parents
Blood type is inherited from the genetic parents at conception, based on the ABO system (A, B, AB, or O) and the Rh factor (positive or negative). This means the baby’s blood type depends entirely on the egg and sperm, not the surrogate’s blood. For example, if the intended mother has type A blood and the intended father has type B blood, their child could have type A, B, AB, or O depending on genetic combinations. The surrogate’s type, no matter what it is, does not affect this outcome.
Doctors do monitor blood compatibility during pregnancy, particularly the Rh factor. If the baby inherits an Rh-positive blood type and the surrogate is Rh-negative, her immune system could produce antibodies against the baby’s blood. This is known as Rh incompatibility. Modern medicine manages this with treatments such as Rh immunoglobulin injections, which prevent complications.
This careful monitoring is an example of how prenatal care supports a healthy pregnancy, but it does not mean that the surrogate influences the baby’s blood type or genetic traits. The baby’s blood type always reflects the genetic contribution of the intended parents or donors.
Rare Cases When Blood Mixing Can Occur
Although the placenta normally keeps the blood supplies separate, small amounts of blood can occasionally cross between surrogate and baby. This is most likely to happen at delivery, during miscarriage, or in rare complications such as placental abruption. When it occurs, it usually involves only a few blood cells and has no effect on the baby’s DNA or identity.
Medical professionals call this “fetomaternal hemorrhage” when fetal blood cells enter the surrogate’s circulation, or the reverse if maternal blood cells enter the baby’s system. These events are uncommon and, when they do happen, they are generally harmless because the body can handle small numbers of foreign blood cells. Doctors may run tests in certain cases, but in most situations, no treatment is required.
It is important to clarify that even if blood mixing occurs, it does not mean the surrogate is contributing genetic material to the child. DNA inheritance is fixed at conception and cannot be changed by a later transfer of blood cells. At most, blood mixing represents a medical detail of pregnancy management, not a shift in parentage or biology. For intended parents, this distinction provides reassurance: the surrogate carries and supports the baby but does not alter the child’s genetic identity.
How the Surrogate’s Body Supports the Baby Beyond Genetics
Creating a Safe Uterine Environment
Once the embryo is transferred to the surrogate’s uterus, her body provides the conditions the baby needs to implant and grow. The uterine lining, known as the endometrium, thickens in preparation to receive the embryo. This lining supplies nutrients in the earliest days before the placenta is fully developed, ensuring the embryo can attach securely and begin developing into a fetus.
The uterus also protects the pregnancy physically. The amniotic sac, filled with amniotic fluid, cushions the baby against bumps or external pressure. This fluid helps regulate temperature and allows the baby to move freely, which is essential for healthy muscle and bone development. The surrogate’s body maintains this environment naturally, adjusting as the pregnancy progresses to safeguard the baby.
In short, the surrogate provides a safe, stable home for nine months, where the baby is shielded from external harm and given the physical space needed for growth.
Providing Nutrients and Hormonal Support
The surrogate’s body plays a crucial role in delivering essential nutrients to the baby through the placenta and umbilical cord. Oxygen, glucose, amino acids, and fatty acids all come from the surrogate’s bloodstream and are transferred to the baby to fuel development. Vitamins and minerals, such as calcium for bones and iron for blood formation, also reach the baby this way. A healthy diet and proper prenatal care ensure these nutrients are consistently available.
Hormones produced by the surrogate’s body are equally important. Progesterone, for example, helps maintain the uterine lining and supports the pregnancy. Human chorionic gonadotropin (hCG) sustains the pregnancy in its early stages, while other hormones regulate the baby’s growth and prepare the surrogate’s body for childbirth. These hormonal signals ensure the baby develops on schedule and that the pregnancy remains stable.
Although the surrogate does not contribute genetic material, her body’s ability to deliver nutrients and regulate hormones is essential for the baby’s survival and healthy development. This biological support is one of the most valuable roles she provides.
Supporting the Baby’s Immune Development
Another way the surrogate’s body supports the baby is by contributing to the development of the baby’s immune system. Through the placenta, she passes antibodies, special proteins that fight infections, from her own immune system to the baby’s circulation. This process, known as passive immunity, gives the baby protection against certain illnesses during the first months of life.
These maternal antibodies can help guard against infections like measles, influenza, and whooping cough until the baby’s own immune system becomes strong enough to function independently. This is why a surrogate’s health during pregnancy is so carefully monitored. If she is up-to-date on recommended vaccines and maintains good overall health, she can pass along stronger immune defenses to the baby.
While these antibodies do not alter the baby’s DNA, they represent a critical form of biological support. They help prepare the baby for life outside the womb, giving intended parents peace of mind that their child benefits from both genetic inheritance and the surrogate’s protective care during pregnancy.
Epigenetics: How the Surrogate’s Body Can Influence Development Without Sharing DNA
What Epigenetics Means in Surrogacy
Epigenetics is the study of how external factors influence the way genes are expressed without changing the DNA itself. Every baby’s genetic code is set at conception and comes from the egg and sperm, but the environment in which the baby develops can “turn up” or “turn down” the activity of certain genes.
In surrogacy, this means the surrogate cannot change the child’s DNA, but her body and environment may affect how some of those genes function. For example, certain genes linked to growth, metabolism, or stress response can be influenced by the uterine environment. These changes do not rewrite genetic inheritance but may shape aspects of the baby’s long-term health.
Understanding epigenetics reassures intended parents that while their child’s DNA remains completely theirs, the surrogate’s role in pregnancy extends beyond carrying the baby. She provides conditions that may fine-tune how some genetic traits are expressed.
Environmental Factors That Shape Gene Expression
Several aspects of the surrogate’s health and lifestyle can influence epigenetic expression. Nutrition plays a central role: a balanced diet rich in vitamins, minerals, and protein supports healthy gene activity related to organ development and brain growth. On the other hand, poor nutrition or deficiencies could increase risks for health issues later in life.
Stress is another factor. High levels of stress hormones, such as cortisol, can affect how certain genes linked to emotional regulation and stress response are expressed. That is why mental health support and stress management are important during a surrogate pregnancy.
Exposure to harmful substances, such as tobacco, alcohol, or environmental toxins, can also influence epigenetics by negatively affecting how genes regulate growth and immunity. This is why medical screening and lifestyle guidelines are essential before and during the surrogacy process. By maintaining a healthy, supportive environment, surrogates help promote the most favorable expression of the baby’s genes.
How Epigenetics Affects the Baby Long-Term
The epigenetic influences experienced during pregnancy may have effects that extend into childhood and adulthood. For example, a surrogate who maintains balanced nutrition and stable health may help promote gene expression linked to strong immune function and healthy metabolism. Research also shows that prenatal environments can affect future risks for conditions such as diabetes, obesity, or cardiovascular disease.
Epigenetics can also shape how a child responds to stress later in life. Babies exposed to lower maternal stress during pregnancy may develop more resilient stress-regulation systems. While genetics determine a child’s potential, epigenetics influences how that potential is expressed in the real world.
Importantly, these influences are environmental, not hereditary. The surrogate does not pass on traits or alter the DNA code. Instead, her body sets the stage for how the baby’s inherited genes operate, providing intended parents with insight into how prenatal care and health choices matter even when DNA is not shared.
What Surrogates Can and Cannot Pass on to the Baby
Babies Don’t Inherit Traits from the Surrogate
In gestational surrogacy, babies do not inherit physical or personality traits from the surrogate. Since all genetic material comes from the egg and sperm, traits such as eye color, hair texture, height, and natural talents are passed down only from the genetic parents or donors. The surrogate’s DNA has no role in determining these features.
This is important for intended parents to understand because it ensures clarity about the child’s biological identity. Even though the surrogate carries the baby for nine months, the child’s genetic code remains tied only to the chosen egg and sperm. The surrogate’s role is to nurture the pregnancy, not to influence inherited traits.
Babies Won’t Resemble the Surrogate Mother
Physical resemblance is determined by DNA, which comes exclusively from the egg and sperm providers. In gestational surrogacy, this means the baby will resemble the genetic parents or donors, not the surrogate. Facial features, body type, and other visible characteristics are rooted in genetics, not in who carries the pregnancy.
Sometimes people wonder if a baby might “pick up” physical traits from the surrogate simply by being in her womb. The answer is no. While the surrogate provides the environment for development, she does not change the baby’s appearance. The only exception would be in traditional surrogacy, which is rarely used today, where the surrogate provides her own egg and is therefore biologically related to the child.
Surrogates Don’t Contribute Their Genes
Genes are passed down at conception, and in gestational surrogacy, the surrogate does not provide genetic material. The embryo is created in the laboratory using the intended parents’ or donors’ gametes (egg and sperm). Once implanted, the surrogate sustains the embryo, but she does not add to its DNA.
This distinction is one of the main reasons gestational surrogacy is so widely practiced in the U.S. It keeps the biological link between intended parents and their child clear, while ensuring that the surrogate’s role is supportive rather than genetic. For families, this provides certainty about their child’s genetic background.
The Surrogate’s Health Can Affect Baby’s Development
Although the surrogate does not influence genetics, her overall health can affect the pregnancy and, by extension, the baby’s development. A surrogate who maintains good nutrition, attends regular medical checkups, and avoids harmful substances creates the best possible environment for the baby to thrive.
For example, proper prenatal vitamins such as folic acid help prevent birth defects, while a balanced diet supports brain and organ development. Regular monitoring of blood pressure, glucose levels, and other health markers ensures that complications are caught early. In this way, the surrogate’s health choices can have a direct impact on how smoothly the pregnancy progresses and how healthy the baby is at birth.
The Surrogate May Influence the Baby’s Temperament
While the surrogate cannot change the baby’s DNA, her environment may influence aspects of temperament and early development. For instance, high levels of stress hormones like cortisol can affect the baby’s stress response systems. A calm and supportive environment may help foster a more stable emotional foundation.
Nutrition also plays a role. A diet rich in essential fatty acids, vitamins, and minerals supports brain development, which can influence cognitive outcomes. While these factors do not determine intelligence or personality, they may shape how genetic potential is expressed, a concept closely tied to epigenetics.
It is important for intended parents to recognize that these influences are subtle and environmental. They complement, but do not override, the genetic inheritance passed down by the egg and sperm providers.
Surrogates Don’t Share Blood with the Baby
As explained earlier, the surrogate’s and the baby’s blood supplies remain separate. The placenta acts as a filter, allowing oxygen and nutrients to pass through while preventing direct blood mixing. This means the baby does not “share blood” with the surrogate in the sense of inheriting anything from her bloodstream.
Even in rare cases where small amounts of blood may cross at delivery, it does not alter the baby’s DNA or biological identity. Intended parents can be reassured that their child’s genetic and blood characteristics come entirely from the egg and sperm, not from the surrogate.
The Surrogate’s Age Affects Pregnancy Health, Not the Baby’s DNA
The surrogate’s age can influence how smoothly the pregnancy progresses, but it does not affect the baby’s DNA. Since the genetic material comes from the egg and sperm, the baby’s biological identity is independent of the surrogate’s age.
However, age may play a role in pregnancy health. Younger surrogates generally have lower risks of complications such as gestational diabetes, preeclampsia, or preterm birth. For this reason, most agencies set age guidelines for surrogates to ensure the safest possible environment for the baby. These guidelines are about health and safety, not about genetics.
Why the U.S. Relies Almost Exclusively on Gestational Surrogacy
Legal Benefits of No Genetic Link
One of the strongest reasons gestational surrogacy has become the standard in the United States is the legal clarity it provides. When the surrogate does not use her own egg, she has no biological connection to the baby. This makes it easier for courts to recognize the intended parents as the child’s legal parents from the start.
Legal agreements and a pre-birth order further strengthen this clarity. These documents establish parental rights before the baby is born, ensuring that the intended parents’ names go directly on the birth certificate. Without a genetic link to the surrogate, there is less risk of disputes about custody or parentage.
In contrast, traditional surrogacy, where the surrogate provides her own egg, creates potential legal challenges. Courts may consider the surrogate a biological parent, which can complicate custody arrangements and delay parental rights for the intended parents. For this reason, most U.S. states and agencies avoid traditional surrogacy altogether and focus only on gestational surrogacy.
Emotional Benefits for Families and Surrogates
Gestational surrogacy also provides emotional clarity for both the intended parents and the surrogate. Because the surrogate is not genetically related to the baby, she is less likely to experience conflicting feelings about her role. She understands her part is to carry and protect the child, but the baby’s identity and genetics belong entirely to the intended parents.
For intended parents, this separation provides peace of mind. They can bond with the pregnancy knowing the baby will be biologically theirs (if using their own gametes) or tied to their chosen donors. This reduces anxiety and helps them feel secure throughout the surrogacy process.
Agencies and clinics emphasize this emotional clarity as one of the biggest advantages of gestational surrogacy. It creates a framework where everyone understands their role, reducing the likelihood of emotional or legal complications. This clarity, combined with strong legal protections, is why gestational surrogacy is the dominant practice in the U.S. today.
Why Choose Surrogacy by Faith
Surrogacy by Faith brings a thoughtful and compassionate perspective to every surrogacy journey. The agency is led by a team of former surrogates who understand the process deeply and are committed to walking alongside each woman with care, respect, and empathy. Their mission is grounded in building meaningful, ethical relationships between surrogates, intended parents, and medical providers.
Surrogacy by Faith is also known for offering generous, transparent surrogate compensation and for coordinating with trusted fertility clinics that align with its values. The agency’s top priority is creating a safe, respectful, and rewarding experience for both the surrogate and the intended parents.
If you’re an intended parent ready to begin, the first step is to explore the intended parent application process. For women interested in becoming surrogates, you can learn more about how it works by reviewing the surrogate mother application process.
Sources:
Cleveland Clinic: https://my.clevelandclinic.org/health/articles/epigenetics
Mayo Clinic: https://www.mayoclinic.org/tests-procedures/in-vitro-fertilization/about/pac-20384716
Mayo Clinic: https://www.mayoclinic.org/tests-procedures/rh-factor/about/pac-20394960
Science Direct: https://www.sciencedirect.com/science/article/abs/pii/S0163638311000750