When we get pregnant, suddenly we’re inundated with information about what to do, what not to do, what to eat, to avoid, and then our prenatal providers ask us to decide on various prenatal testing options.
The amount of information can be overwhelming. Way back when I was pregnant, I wanted to make sure everything was ok with the baby and decided to have an amniocentesis to screen for Down Syndrome and other serious genetic conditions. It was scary, because even though there was a very low risk of miscarriage, it was still a possibility. I remember wanting to make sure the baby was okay, but being worried about the risks of the test.
Then a few years later, with developments in genetic testing, we could screen for Genetic Conditions in a baby simply by drawing a blood sample from a pregnant mom after 10 weeks of pregnancy. That’s because within the mom’s bloodstream are fragments of the baby’s DNA. This is known as cell-free DNA (cfDNA). This means that a newly pregnant mom can provide a sample of her blood at 10 weeks and her baby can be evaluated for Genetic Conditions, all without any risk of miscarriage.
What is Tested For?
NIPT screens for chromosomal abnormalities. These occur in about one in 150 live births. When we think about that in context it means that 149 out of 150 babies will not have a chromosomal condition.
A deeper dive into the biology.
Every cell in our bodies contain 23 pairs of chromosomes, equaling a total of 46 chromosomes. The egg provides half of the genetic material, which is 23, and the sperm provides half, also 23. When the egg and sperm get together, they merge their chromosomes to create 23 pairs of chromosomes.
Sometimes however, when the egg and sperm come together, an extra chromosome comes along, so instead of a pair, there can now be 3 chromosomes present, which is known as a “trisomy” Many of these chromosomal trisomies result in a miscarriage early in the pregnancy.
NIPT screens for the three most common chromosomal trisomies:
- Down Syndrome (trisomy 21) – Trisomy 21 means there are 3 (tri) copies of chromosome (somy) 21.
- Edwards Syndrome (trisomy 18) – There are 3 copies of the 18th chromosome. This is a rare and serious condition, and most of these babies die before or soon after birth.
- Patau syndrome (trisomy 13) – the least common of the autosomal trisomies and most severe. Newborns born with Patau syndrome often have physical abnormalities or intellectual issues. 90% of babies with Patau die prior to birth.
What else can NIPT detect?
NIPT can also detect the baby’s sex. Yes, as early as 10 weeks, you can find out if you’re having a boy or girl.
NIPT can also detect what are known as sex chromosome disorders. These are disorders associated with either the X gene or the Y gene. These chromosomes determine our biological sex. Males have XY and Females have XX.
Sex chromosome disorders occur when there is extra or missing X or Y chromosome.
NIPT tests for the following sex chromosome disorders:
- Klinefelter’s syndrome (XXY syndrome) the most common affecting males, their testicular growth, hormones and fertility.
- Jacob’s syndrome (XYY syndrome) occurs in about 1 out of 1000 male children; causes growth delays, low muscular development and physical malformations.
- Trisomy X (triple X syndrome) affects about 1 in 1,000 females. Females normally have two X chromosomes in all cells — one X chromosome from each parent. In this case though, there are 3 X chromosomes. Symptoms can vary greatly among girls and women, some are mild, but can include above average height, learning disabilities, psychological problems.
- Turner’s syndrome (monosomy X) affects only females, this occurs when one of the X chromosomes is missing or partially missing. Turner’s syndrome can cause a variety of medical and developmental challenges from short height, underdeveloped ovaries, and heart defects, to infertility.
What’s the Accuracy of NIPT?
NIPT discovers more than 99% of cases of Down Syndrome. But it is still not considered a diagnostic test, it is a screening test. The only way to be absolutely certain about any of the chromosomal conditions, Down Syndrome, for example, would be to have the amniotic fluid tested, as I did, or using chorionic villus sampling (CVS).
Who Should Get NIPT?
Some laboratories offer additional testing for many conditions. Talk with your healthcare professional to determine which company they use for their NIPT and which specific conditions will be included in your results.
The American College of Obstetricians and Gynecologists previously recommended NIPT only for pregnant people who were considered at high risk based on their age, personal or medical history, or family history. However, the latest recommendations state that providers should offer all pregnant patients NIPT, regardless of their risk.
While the risk of chromosomal abnormalities increases with a pregnant person’s age, these disorders can occur at any age. Other factors associated with an increased risk include:
- Abnormal ultrasound findings
- A chromosomal disorder present in either parent of the baby
- A previous pregnancy with a chromosomal abnormality
What if the NIPT is positive?
When parents are notified of positive NIPT results, the next steps can feel overwhelming. It’s important to talk to your prenatal provider and a genetic counselor about what these tests mean, what the options are for more accurate testing and then taking the time to consider what to do next.
The next testing options are having a diagnostic test with a higher level of accuracy such as CVS or Amnio. These tests are only performed by physicians with advanced training.
CVS: Chorionic Villus Sampling is done from 10-14 weeks. Chorionic villus sampling takes a tissue sample of the developing placenta, which is known as the Chorionic villus and analyzes the chromosomes. Unlike NIPT, this is considered invasive, and there is a slight chance of miscarriage.
Amniocentesis: This is done after 16 weeks. With an amniocentesis, a small amount of amniotic fluid that surrounds the baby is removed to analyze the baby’s cells. Don’t worry, the baby will make more fluid. Unlike NIPT, this is considered invasive, and there is a slight chance of miscarriage.
And remember, NIPT will also reveal the baby’s sex, so be sure to let your healthcare professional know if you want this information or prefer to be surprised on your delivery day.
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