Sex Selection

Sex selection at a glance

• Sex selection, also known as gender selection or embryo sex selection, is when parents undergoing in vitro fertilization (IVF) select to implant a resulting embryo based on its sex.
• Preimplantation genetic testing (PGT) makes sex selection possible by evaluating the genetic makeup of each embryo tested.
• Medical concerns and genetic issues that may result in failed pregnancy or birth defects typically lead to the decision for sex selection.
• Family balancing, a conscious effort to have a certain mix of child genders, is another reason people may choose sex selection.
• Sex selection can bring up social and ethical issues, including sexism and gender imbalance, that parents and their fertility doctor will discuss.

What is sex selection?

Sex selection provides hopeful parents with embryos created through IVF the option to choose the sex of their baby prior to implantation and pregnancy. Parents may decide to use sex selection for a variety of reasons including medical concerns, family balancing and genetic issues.

A combination of IVF and PGT makes sex selection possible. During IVF, an embryo is created when a woman’s egg(s) is fertilized by a man’s sperm outside of the body in a lab. Embryos are then evaluated and chosen for implantation.

During the embryo evaluation process, parents may choose to use PGT to test for a specific genetic disorder that one or both parents is suspected of carrying and could pass on to their child.

Most humans have 23 pairs of chromosomes (22 pairs of numbered chromosomes, and 1 set of sex chromosomes, XX for females and XY for males). An abnormal embryo chromosome number means the embryo has either too many or too few chromosomes. This phenomena occurs incredibly frequently, in 1/3 to 2/3 of all embryos, or even more frequently, depending on the female’s age.

PGD can test the number of chromosomes in an embryo, including the number of sex chromosomes. Having an abnormal number of sex chromosomes is a frequent cause of failed implantation or miscarriage, examples include a single X chromosome as in Turner syndrome (45X), or an extra X chromosome in males as in Klinefelter syndrome (47XXY).

Because the sex chromosomes are evaluated in the genetic test for chromosome number, the test reveals whether the embryo is a girl (X & X chromosomes) or a boy (X & Y chromosomes). All eggs a woman produces are inherently “female” because women can only contribute X (female) chromosomes to an embryo. The male sperm can contribute either an X (female) or a Y (male) chromosome, which determines the sex of the embryo.

IVF and PGT cannot be used to create only boy or only girl embryos, rather, IVF and preimplantation genetic testing can show whether the embryos that the couple has created are boys or girls, and whether they have a normal number of chromosomes (46) or an abnormal number of chromosomes which would limit their ability to implant and grow. Many parents chose to utilize PGD when they have no known genetic diseases in the family, but want to decrease the likelihood that they transfer an embryo with abnormal chromosomes.

What sex selection is not

Sometimes sex selection is referred to as “gender selection.” Sex selection is becoming the most accurate term, as it determines whether the child will be a genetic male (XY) or genetic female (XX). Gender is increasingly being used to describe how individuals identify as a man or a woman or sexual orientation. The techniques described here cannot determine sexual orientation or gender identity.

Why use sex selection?

Family balancing

The majority of couples who seek sex selection of their IVF embryos do so for non-medical reasons often referred to as family balancing. Families who have more than one child of a sex may select a pregnancy of the opposite sex in order to provide variety in the family.

The reasons for selecting a particular sex are based on personal preferences. Some cultures have a predisposition toward male children, particularly in the first child. On the other hand, some people desire female offspring. Some fathers are keen to have a son and experience that male bond, others may wish to have a daughter. Some couples may have lost a child and wish to have another child of the same sex.

Medical concerns

Some individuals who need IVF in order to become pregnant will use PGT (PGT-A or PGT-M) to decrease the chance of miscarriage by screening for genetic abnormalities. Parents may choose to be informed about the embryo’s sex at this time and to select an embryo of a certain sex.

Hopeful parents may also use sex selection to prevent the birth of children affected by certain sex linked genetic disorders. These diseases include hemophilia, muscular dystrophy and fragile-X syndrome. Many genetic disorders, including muscular dystrophy, are more likely to affect males. Sex selection allows couples to choose female or unaffected male embryos in order to prevent the risk of these genetic disorders in their children. Preconception screening for genetic disorders can help patients determine if gender selection would be beneficial.

Smaller families, delayed families

These days, people are having smaller families, which reduces the odds of having a child of a particular sex. When people had more children, this wasn’t as much of an issue. If a couple only plans to have one child, they may choose the sex they want, as they know they are not having more children. This can also happen with a single mother who knows she will only have one child.

As more women delay having a family to pursue careers or for other reasons, they are more likely to need assisted reproductive technologies such as IVF to achieve pregnancy. While participating in IVF, they may opt for PGD and select the sex of their embryo.

Social issues and ethical concerns of sex selection

Sex selection for non-medical reasons presents ethical concerns for reproductive medicine clinics and providers. The decision whether or not to offer this service in the United States depends on the individual practice. It is outlawed in some countries.

While many clinics do not offer sex selection, TRM does and works with the potential parents to address ethical issues, including the following:

Sexism and discrimination

Having the ability to choose sex may lead to sexist stereotypes and discrimination toward one sex over another.

Natural sex ratio imbalance

Controlling sex could result in one gender becoming more predominant than the other, leading to gender imbalance. For instance, the Chinese population has shifted out of balance and has more males as a result of the country’s previous “one child” rule. Many couples who were pregnant with a girl had abortions due to the cultural preference for a male child, which they hoped for in the next pregnancy.

Leftover embryos

The issue of what to do with embryos that are not implanted because they are of the un-preferred sex is highly problematic for many people. This involves making decisions about embryo disposition ahead of time, and is a situation any couple faces using IVF, whether or not sex selection is being chosen. Fortunately, couples have options, which can include donating the unused embryos to other couples, donating the embryos to improving medical science, or discarding the embryos.

Miscarriage regret

While not all patients react the same, doctors have noticed that couples who face miscarriages after having gone through sex selection have a harder time dealing with the loss of the pregnancy.