Finding out whether you are going to be having a boy or a girl can be really
fun or nerve wracking. In the past, this could only be done through the doctor's
office with ultrasound or an invasive test such as an amniocentesis. More recently,
at home test kits for determining gender have become available. How do these tests work? Are
they accurate? Should you trust the results? Find out on today’s episode of InfertilityTV
First a little background. The sex of an embryo is determined by genetics. Male embryos
have a one Y chromosome and one X chromosome. Female embryos have two X chromosomes. Most
tests for determining the sex of an embryo or developing fetus are therefore looking at the
presence or absence of a Y chromosome. If a Y chromosome is detected, then the test
result will be male. If no Y chromosome is detected, then the test result is female.
What is a chromosome? A chromosome is a molecule contained in the nucleus of a
cell which is made up of DNA and protein. The proteins in a chromosome allow the DNA
to be scrunched up very tightly to fit into the cell nucleus. The DNA of a chromosome is
divided up into sections called genes. Each gene has a specific role or function. For example,
the Y chromosome has a gene called the SRY gene which makes a protein
that causes testicles to develop in the fetus instead of ovaries.
Entire cells containing DNA from the fetus or the placenta can enter the mother’s blood
circulation. Some cells of the fetus or placenta will degenerate and release their contents,
including DNA, which can also enter the mother’s blood. In both cases,
fetal DNA enters the mother’s blood. When DNA is released from a cell it is called cell free
DNA. If it comes from the fetus, we call it fetal cell free DNA. Approximately 10% of the
total cfDNA in a pregnant person in the second trimester comes from the fetus. A blood sample
obtained after 9 to 10 weeks’ gestation has enough fetal free DNA to be detected.
At your doctor’s office, maternal blood tests for fetal cell free DNA can help
to identify a fetus with abnormalities such as Down’s Syndrome in which the fetus has an
extra copy of chromosome #21. In the same way, blood tests can be done to
see if there is fetal cell free DNA from the Y chromosome in the mother’s blood.
So, it is technically possible to detect DNA from a Y chromosome with a blood test and therefore
to determine if the fetus is genetically male. But how accurate are these tests? This depends
on two important factors. How much fetal cell free DNA is present in the mother’s
blood and how sensitive a particular test is. Failure to detect Y chromosome DNA from a male
fetus could mean the test mistakenly calls it a girl. Saying there is Y chromosome DNA
when there isn’t would result in the test saying the fetus is a male when it is really a female
I should point out that there are no high quality studies in this area. Almost all of
the high quality studies have used this technology to detect chromosome abnormalities - not gender.
Some of the companies offering at home gender tests have done studies to look at the accuracy
of their tests but those results may not indicate if it will be accurate for you. Why not? First,
the number of people studied so far is so small that it is impossible to make definite
conclusions. Second, during a study, these tests are performed by experienced scientists
under controlled conditions. I have not found any studies that looked at the accuracy when average
people are trying these tests at home. We really don’t know if the results would be the same for
people doing this at home. For example, one study used a needle to draw 3-4 mL of blood from their
study subjects. At home, people are getting only a few drops of blood from a finger stick. This could
dramatically affect the accuracy. DNA is very fragile and there is a very small amount of fetal
cell free DNA in the blood. Sending blood through the mail to the testing laboratory increases the
chance that DNA might be degraded when it reaches the lab and therefore give an incorrect result.
Our InfertilityTV Bottom line is this. At home testing for fetal genetic sex is possible
but the accuracy of these tests is really unknown. If you are doing this test for fun,
then go ahead. There is at least a 50% chance that you will get the correct answer. If not,
no harm done. Plus you can usually get your money back from the company if the test was
wrong. However, if you are doing this test because you have a sex linked genetic disease
that runs in your family, I would not rely on these tests to tell you whether
you could have a fetus at risk for a genetic problem. I would also not commit to spending
a lot of money on a gender specific nursery design in your home based on these results.