Preconception sex selection may have once seemed like a far-fetched concept but it is now a commonplace reality. The term refers to any procedure which attempts to influence the sex of offspring before pregnancy. There are several methods currently in use, each with their own success rates, pros and cons. A clear look at all of your options will allow you to decide whether preconception sex selection is right for your family.

Typical reasons to select gender:

There are many reasons why parents may want to control the sex of their baby. Personal preference and cultural attitudes have traditionally influenced these desires, and there has been ongoing debate about the ethics of using preconception sex selection for these reasons and whether it could perpetuate discrimination, particularly towards female children. For these reasons, some countries have banned elective selection. It is perfectly legal in the United States, though some fertility clinics have their own policies about when they will or will not perform these procedures. Each family and their fertility doctor must navigate these choices together, but there are two situations where the use of preconception sex selection is generally approved:

• When medically indicated to screen and prevent sex-linked genetic disorders: This is the initial reason that the process of sex selection was invented. Doctors wanted to be able to select for female infants when one parent carries an X-chromosome linked genetic disorder. In these disorders, such as hemophilia or certain types of muscular dystrophy, female children may become carriers for the disease but are generally unaffected, while male children are likely to suffer from the disorder.  

• When used electively for family balancing: If couple already have one or more children of the same sex, they may want their next child to be of the opposite sex.

Sex selection techniques:

There are several technologies available today. The cost, invasiveness and effectiveness vary widely between processes. Here is a basic overview.

Sperm processing to enrich for a particular sex chromosome.

This is preconception process, which means that the goal is to create embryos of one sex or another by controlling which sperm are used in fertilization. Processing sperm creates an “enriched sample” which means that the sample will contain mostly (but not exclusively) sperm of the desired sex. This sperm can then be used to fertilize an egg, either in the woman’s body through IUI, or in a lab through IVF. There are two different techniques that are widely used to separate the X chromosome sperm from the Y chromosome sperm.

• Sperm spin: Used with IUI. X sperm contain slightly more genetic material than Y sperm, which creates a minute difference in weight. This technique uses various density gradients to separate heavier X sperm from the lighter Y sperm. Because this is a preconception method, you may be able to use IUI, which is less invasive and less expensive than IVF, but because IUI is not as effective as IVF, there are lower pregnancy rates overall. Success rates: Limited studies suggest 60-65% when enriching for both male and female sperm.
• Flow cytometry: Used with IVF. In this technique, a special fluorescent dye is added to the sperm sample. Experts can then use laser technologies to see how the dye binds to the genetic material in the sperm. Because the X sperm has about 2.8% more genetic material than Y sperm, the dye causes the X sperm to fluoresce (or glow) brighter. Flow cytometry is sometimes referred to by the brand name MicroSort®. Success rates: 60-75% when enriching for male sex, and 70-85% when enriching for female.

Pros and cons of sperm spin/flow cytometry

• Pros
  • Less expensive than preimplantation genetic diagnosis (PGD)
• Cons
  • Less effective than PGD for sex determination
  • MicroSort® is not available in the USA

Preimplantation genetic diagnosis (PGD): chromosomal analysis of an embryo 

This is a newer technique which has emerged in the past decade. PGD allows an expert to look at the chromosomes of an embryo, and has been used to screen for many genetic diseases and abnormalities. Because it is also possible to tell the sex of an embryo by examining the chromosomes, it is the most effective method of sex selection available. PGD is used in conjunction with IVF, which means that the woman will need to undergo a series of procedures to induce ovulation, retrieve eggs, and eventually transfer the chosen embryo. Fertilization occurs in the lab, and the created embryos are cultured for several days, up to the blastocyst stage. The embryologist then very carefully removes a few cells from the viable embryos to test. Only an embryo (or embryos) of the desired sex are then transferred into the woman’s uterus. Success rates: >99% correct sex identification and selection

Pros and cons of PGD

• Pros
  • This is the most effective method for ensuring gender.
  • Remaining embryos can be frozen for future frozen embryo transfer (FET) which means you may be able to use the embryos from a single cycle to build your entire family.
  • PGD also verifies which embryos are healthy genetically and which embryos are abnormal. This offers great peace of mind by increasing the chance of having a healthy baby. Because genetic abnormality is a leading cause of miscarriage/pregnancy loss, it can also help some women carry a baby to term for the first time.
• Cons
  • Same risks as IVF: IVF is associated with a small number of risks, such as (very low) risk to embryo. There is a small chance that the process of PGD could damage an embryo. Waiting longer to test the embryo and giving it more time to develop can help. Many clinics have found that testing after day 5 instead of day 3 can reduce risk. Make sure the fertility clinic you choose is experienced in PGD. You should feel comfortable asking about numbers and success rates.
  • You will need to decide what to do with any unused embryos. This is not so much as con as a consideration. Your options are to freeze, discard, or donate for adoption or research.

Old wives’ tales about how to influence the sex of your baby are found in just about every culture, passed down through generations and circulated through centuries. Anecdotal evidence may vary, but scientifically these methods all seem to have one thing in common: a 50/50 chance of producing a girl or boy baby. Today, however, parents who would like to choose the sex of their baby have new, much more effective options. Knowing the sex of your baby before they are born can be a wonderful thing for any expectant parent, whether it is a surprise or a carefully considered decision.