Diagnosis of Down syndrome
Diagnosing Down syndrome involves a multi-step process that typically begins with prenatal screening tests for pregnant individuals who are considered to be at higher risk of having a child with the condition. These screening tests include:
Ultrasound: An ultrasound scan is used to assess fetal development and can sometimes detect physical markers associated with Down syndrome, such as increased fluid at the back of the baby’s neck (nuchal translucency). However, ultrasound alone cannot provide a definitive diagnosis of Down syndrome.
Maternal Serum Screening: This blood test measures the levels of certain substances in the mother’s blood, such as alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol. Abnormal levels of these substances may indicate an increased risk of Down syndrome, although it is not diagnostic.
If the results of these screening tests suggest an elevated risk of Down syndrome, further diagnostic testing may be recommended. The two main diagnostic procedures used to confirm a diagnosis of Down syndrome are:
Amniocentesis: During this procedure, a small sample of amniotic fluid surrounding the fetus is collected using a needle inserted into the mother’s abdomen under ultrasound guidance. The cells in the amniotic fluid, which include fetal cells, are then analyzed for chromosomal abnormalities, including an extra copy of chromosome 21 (trisomy 21).
Chorionic Villus Sampling (CVS): CVS involves taking a sample of cells from the placenta, either through the cervix (transcervical CVS) or through the abdomen (transabdominal CVS). Like amniocentesis, these cells are analyzed for chromosomal abnormalities, providing a definitive diagnosis of Down syndrome.
It’s important to note that both amniocentesis and CVS carry a small risk of complications, including miscarriage, so the decision to undergo these procedures should be made after thorough discussion with healthcare providers and consideration of individual circumstances.
In cases where Down syndrome is not diagnosed prenatally, it can still be identified after birth based on physical characteristics such as facial features, along with developmental and medical evaluations. Confirmation of the diagnosis is typically obtained through genetic testing, which involves analyzing a blood sample to examine the individual’s chromosomes for the presence of an extra chromosome 21.
Early diagnosis of Down syndrome allows for early intervention, including access to medical care, developmental support, and educational resources, which can greatly improve outcomes and quality of life for individuals with the condition.
