The first part of the test involves an ultrasound that will measure the nuchal translucency (NT). This is a first tier test that can either be reassuring or help guide decisions about potential follow-up testing. It cannot be used to diagnose or rule out a chromosome abnormality in a pregnancy. A mother’s risk decreases as the pregnancy progresses due to the risk of natural miscarriage.įirst off, it’s important to know that a “screening” test will just provide you with a more accurate risk assessment. It provides a specific risk for Down syndrome and a risk for all chromosomes abnormalities (which includes Down syndrome, trisomy 18, and trisomy 13). Below is an example of a maternal age risk chart. As a woman get older, the risk for chromosome abnormalities in a pregnancy increases. If the pregnancy makes it to term, the vast majority of babies won’t live past 1 year of life.įor a more detailed discussion of chromosomes and chromosome abnormalities check out this link.īefore any prenatal testing is performed, a risk approximation for chromosome abnormalities can be given based on maternal age. Most pregnancies with trisomy 13 or 18 will result in a miscarriage. Both of these chromosome abnormalities are more severe than Down syndrome and are generally considered fatal conditions. Two other chromosomal trisomies that are sometimes compatible with life and those are trisomy 18 and trisomy 13. A trisomy can occur in any chromosome pair, but most will result in an early miscarriage before you even know you’re pregnant. Down syndrome is a common chromosome abnormality, occurring in approximately 1 in every 800 recognized pregnancies. This is called trisomy 21 (see image), but is more commonly referred to as Down syndrome. For example, if one of the sex cells has an extra chromosome 21, the resulting fetus will have three copies of chromosome 21 instead of two. However, sometimes errors are made in this process that can cause some of the sperm cells and egg cells to have extra or missing chromosomes. This is important so that when the sperm fertilizes the egg there are a total of 46 chromosomes (half from mom and half from dad). During meiosis, a process of cell division, sex cells (sperm and eggs) are created that contain only one copy of each chromosome. For each chromosome pair, we inherit one chromosome from our mother and one chromosome from our father. The first 22 pairs of chromosomes are called autosomes and the last pair are the sex chromosome (XX for girls and XY for boys). A chromosome is made up of tightly wound DNA and can be thought of as a genetic blue print that determines everything from our hair color to our risk for genetic disease. Typically, we have 23 pairs of chromosomes in each cell of our body. To understand what a chromosome abnormality is we have to take a step back and talk about some basic genetics. Noninvasive Prenatal Testing (Materniti21, Verifi, Panorama, Harmony).Second Trimester Screening (the quad screen).First Trimester Screening (the nuchal translucency test).My goal is to take a nondirective approach of explaining the commonly available prenatal screening options. In discussing these testing options I am not advocating for or protesting against the issue of abortion. Other women may use the information to guide decisions such as termination and adoption. Many women like to have the information provided by these tests to prepare for when the baby is born. Certainly there are women who choose not to have any prenatal screening done. Prenatal screening for chromosome abnormalities should be made available to all women during all pregnancies (as recommended by the American Congress of Obstetricians and Gynecologists). It is important to remember that all of the following are OPTIONAL during a pregnancy. Below is a review the common prenatal screening options that are available along with the pertinent limitations and benefits of each. It can be difficult to understand all of the options and decide what is best for you. With advancing technology, the available options are becoming overwhelming for both health care professionals and patients. Prenatal screening for genetic conditions has become a complex process with a multitude of tests to choose from.
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