Surrogacy is a family-building option that involves another person carrying a pregnancy for intended parents. A common inquiry for those exploring or learning about surrogacy concerns the genetic relationship between the baby and the surrogate mother. Understanding the different types of surrogacy helps clarify how genetic material is passed on in each scenario.
How DNA is Passed On
Deoxyribonucleic acid (DNA) is the blueprint for an organism’s development and function. In humans, DNA is organized into structures called chromosomes, which reside within the nucleus of most cells. A baby inherits half of its nuclear DNA from the biological mother’s egg and the other half from the biological father’s sperm. Each human egg and sperm cell carries 23 chromosomes, combining at fertilization to form a complete set of 46 in the embryo. This process ensures that the offspring receives a blend of genetic traits from both biological parents, with nuclear DNA dictating characteristics such as eye color, hair color, and other inherited traits.
Traditional Surrogacy and Genetics
Traditional surrogacy involves the surrogate mother providing her own egg, which is then fertilized. This fertilization can occur either through artificial insemination using the intended father’s sperm or donor sperm. In this arrangement, the surrogate mother is genetically related to the baby because her egg contributes half of the baby’s nuclear DNA. This makes her the child’s biological mother, meaning the baby will share DNA with the traditional surrogate. This method of surrogacy is less common today compared to gestational surrogacy due to the direct genetic connection and associated legal and emotional complexities.
Gestational Surrogacy and Genetics
Gestational surrogacy is the most prevalent form of surrogacy currently practiced. An embryo is created outside the body using in vitro fertilization (IVF). The embryo is formed from the egg and sperm of the intended parents, or from donor egg, donor sperm, or a combination of both. This embryo is then transferred into the gestational surrogate’s uterus. In this process, the surrogate mother does not contribute any nuclear DNA to the baby; the baby’s entire nuclear genetic makeup comes solely from the egg and sperm used to create the embryo. Therefore, there is no genetic link between the gestational surrogate and the baby she carries, as her role is to provide the uterine environment for development.
What Else Does the Surrogate Contribute?
While a gestational surrogate does not contribute nuclear DNA, her role in the baby’s development is still significant. Mitochondrial DNA (mtDNA) is inherited exclusively from the egg donor, whether that is the intended mother or an egg donor, and not from the gestational surrogate; mitochondria are the “powerhouses” of cells and contain their own small circular DNA. The uterine environment provided by the gestational surrogate plays a crucial role in the baby’s growth and development. Factors such as the surrogate’s overall health, nutrition, lifestyle choices, and stress levels during pregnancy can influence the baby’s development. These influences can lead to epigenetic changes, which are modifications to gene expression that do not alter the underlying DNA sequence but can affect how genes are turned on or off.