There is no way to diagnose whether your baby has Down syndrome with 100 percent certainty. However, there are some tests which–when combined with each other and risk factors like your age and your family history–can give you an estimation of the likeliness that your baby carries the trisomy 21 gene, which causes Down syndrome. Diagnostic tests are also available, which can tell you whether your baby carries the gene, but they come with the risk of miscarriage.
Triple Screen Test
Your doctor will give you a triple screen test in your first trimester, around week 16 to week 18 week. It tests the levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and estriol in your bloodstream. If you receive abnormal results, the doctor will combine this with your other risk factors–advanced age in particular–to tell you the chance of carrying a baby with Down syndrome. Abnormal results do not indicate that the baby has Down syndrome definitively, but you may want to consider further testing, according to the University of California at San Francisco Medical Center.
Nuchal Translucency Screening
Nuchal translucency (NT) screening is not available at all hospitals, but it is able to give you an earlier peek into your chances of carrying a Down syndrome baby. Doctors use a high-resolution ultrasound to look at the back of your baby’s neck–the nuchal area. Like the triple screen, this is not a hard-and-fast diagnosis, but it can catch 80 percent of Down syndrome cases. You should consider further testing if you are concerned.
In amniocentesis, doctors insert a long needle to retrieve a bit of the amniotic fluid. This will contain skin cells from your baby, which doctors can then use to search for the trisomy 21 gene. Amniocentesis will test for other genetic disorders in your baby as well. It has a high level of accuracy. Unfortunately, there is a risk of harm to your baby; it could cause you to have a miscarriage.
Chorionic Villus Sampling
In chorionic villus sampling (CVS), doctors take a small piece of the placenta–which has the same cells as your baby–and use it to test for chromosomal defects like Down syndrome. There is less than a 1 percent chance of miscarriage, but some parents feel that this is too great and opt not to have this type of testing. The advantage to CVS is that your doctor can diagnose Down syndrome earlier.
When looking at the ultrasound, there is a chance that the technician will detect some signs of Down syndrome in your baby. These include an increase of skin in the nuchal area, decreased femur size or cysts in the brain. The ultrasound alone, however, cannot diagnose Down syndrome, according to the American Academy of Family Physicians.
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