At Tallahassee Perinatal Consultants, we talk to all patients about optional screening for chromosomal problems such as Down syndrome, trisomy 18 and trisomy 13.
Chromosomes are the structures that hold our genes. Genes are the individual instructions that tell our bodies how to develop and keep our bodies running healthy. In every cell of our body there are approximately 20,000 genes that are located on 46 chromosomes. These 46 chromosomes occur as 23 pairs. We get one of each pair from our mother in the egg, and one of each pair from our father in the sperm. The first 22 pairs are labeled longest to shortest. The last pair are called the sex chromosomes labeled X or Y. Females have two X chromosomes (XX), and males have an X and a Y chromosome (XY). Therefore, everyone should have 46 chromosomes in every cell of their body. If a chromosome or piece of a chromosome is missing or duplicated, there are missing or extra genes respectively. When a person has missing or extra information (genes) problems can develop for that individual’s health and development.
For patients who meet “high-risk” criteria, we may also discuss a non-invasive prenatal testing method called cell-free fetal DNA. Although all patients begin with an age-related risk for having a baby with a chromosome problem such as Down syndrome or trisomy 18, these screens allow us to identify pregnancies that may be at a higher risk of being affected by one of these chromosome conditions. First and second trimester screens and cell-free fetal DNA are done by performing a maternal blood draw and therefore do not pose any risk to the baby. As with any type of screen, some patients can have false positive or false negative results.
If the first or second trimester screen results return as positive, we recommend discussing other testing options such as non-invasive prenatal testing with cell-free fetal DNA or diagnostic testing with a genetic amniocentesis.