The gender of an embryo is determined at the moment of fertilization, when the sperm's X or Y chromosome pairs with the egg's X chromosome. In natural conception, this process is left to chance, in IVF you can learn the gender of an embryo even before the embryo is transferred, through Preimplantation Genetic Testing (PGT).
PGT allows fertility specialists to analyze embryos at a genetic level, identifying their gender before implantation.
By opting for PGT during IVF, intended parents can choose the sex of their baby with accuracy, helping to plan for family balance or avoid sex-linked genetic disorders.
Find out more about PGT and embryo testing here.
Read on to learn more about when an embryo’s gender is determined and how it can play a part in your IVF journey.
When is an Embryo’s Gender Determined?
An embryo’s gender is determined at the moment of fertilization. An embryo’s gender is determined by the chromosomes of the sperm and egg that form it, which means that an embryo’s gender is determined at the time that the sperm and egg combine.
The biological sex of the embryo is established when a sperm carrying either an X or Y chromosome fertilizes the egg, which always carries an X chromosome. If the sperm carries an X chromosome, the embryo will be genetically female (XX). If the sperm carries a Y chromosome, the embryo will be genetically male (XY).
The physical characteristics related to sex start to develop later, typically around 7 weeks into pregnancy. For couples undergoing IVF, sex can be identified through preimplantation genetic testing (PGT), which screens the chromosomal make-up of the embryos before transfer.
How Can You Tell the Gender of an Embryo? [PGT and Gender Selection]
You can find out the gender of an embryo in IVF before the embryo is transferred to the uterus through Preimplantation Genetic Testing (PGT).
In PGT, a single cell or small number of cells are taken from the embryo and are evaluated for the presence of X and Y chromosomes during the genetic screening.. An embryo with two X chromosomes (XX) is female, while an embryo with one X chromosome and one Y chromosome is male (XY).
Can You Choose the Gender of an Embryo?
Technically, yes. Embryo gender selection is possible in some cases but not in all cases when you undergo IVF. When you create embryos, your medical team can help you determine the sex of all of your embryos through Preimplantation Genetic Testing (PGT).
The gender of an embryo cannot be modified or changed, but you can choose your preferred gender if you have embryos of that gender. That being said, sex selection of embryos is only one factor in determining which embryo is transferred.
Embryo Genetic Testing Results
When the embryos undergo PGT testing, you will learn more information than just the sex of the embryo, including information about potential genetic disorders, and your medical team will grade each embryo to determine which embryos have the highest likelihood of developing into a pregnancy.
As you consider the sex of the embryo, you may also consider factors like the health of each embryo and the development of each embryo, which can determine the success of your pregnancy.
For example, if you create three embryos before you undergo IVF and you are hoping for a girl, you could have any number of combinations of information like this:
- You have three male embryos and would need another round of embryo creation to potentially have a female
- You have three female embryos and you need to choose which one to use
- You have two male embryos and one female, but the female embryo has markers of a genetic disease
- You have two female embryos and one male embryo, but the male embryo has the highest likelihood of a successful pregnancy
- And other combinations
As you can see, if you have all male embryos, it would not be possible to choose a female embryo, and in some cases, your family will need to weigh your desired sex outcome with other potential outcomes. You can read more about embryo genetic testing results here.
Can Frozen Embryos Be Tested for Gender?
Yes. If your embryos did not receive genetic testing before freezing, you should know that embryos can still undergo genetic testing after freezing. That means that choosing embryo gender is possible for frozen embryos.
Exceptions: Genetic Disorders That May Affect Gender Determination
Some genetic disorders affect the ability to determine gender at birth or before birth. For example, people with androgen insensitivity may be born with an XY chromosome, which is typical for males, but may have typical external characteristics for females and be raised female. Other disorders that may affect gender determination include Turner Syndrome, Klinefelter syndrome, mixed gonadal dysgenesis, XY male hypospadias, and ovotesticular syndrome.
What is the Difference Between Sex of an Embryo and Gender?
While “sex” and “gender” are used interchangeably in this article and elsewhere, in scientific literature, biological sex is determined by the chromosomes that form an embryo, while the definition of gender is more commonly debated and is often used to refer to human-specific sociological patterns that are associated with sex differences.
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Frequently Asked Questions
At what point does an embryo become a boy or girl?
Gender is determined by sex chromosomes in the sperm. Sperm can contain either an X chromosome or a Y chromosome, which means that when the egg and sperm join, the sex of the embryo is decided.
At what stage does a fetus determine gender?
Sex is determined by the DNA in the sperm and the egg that combine to create an embryo, so the sex of a baby can be determined from the time the sperm and egg combine to form an embryo.
Can you determine the gender of an embryo?
Yes, you can determine the gender of an embryo from Preimplantation Genetic Testing (PGT) when you use IVF. If you are not using assisted reproduction like IVF, it may be longer until you can determine the gender of your embryo.
How early can a baby's gender be determined?
A baby’s gender can be determined within the first few weeks, and if you are using IVF, you may be able to determine the sex of your embryos even before they are transferred to the uterus.