What is Down syndrome in pregnancy?

Down syndrome, also known as Trisomy 21, is a genetic condition present from conception where an individual has an extra copy of chromosome 21. Chromosomes are small "packages" of genes within the body's cells that contain the instructions for how the body forms and functions. During pregnancy, when a baby with Down syndrome is growing, this extra chromosome changes how their body and brain develop.

Understanding Down Syndrome

Normally, a baby inherits 23 chromosomes from each parent, resulting in a total of 46 chromosomes. In Down syndrome, there's an extra, or third, copy of chromosome 21, leading to a total of 47 chromosomes. This additional genetic material alters the developmental trajectory of the baby, leading to a range of potential physical and intellectual characteristics.

How Does it Affect Development?

The presence of an extra chromosome 21 during the baby's growth in the womb influences various aspects of development. These changes can result in:

• Distinct Physical Features: Babies with Down syndrome often share certain recognizable physical traits. While these vary, common features can include an upward slant to the eyes, a flattened facial profile, a single deep crease across the palm of the hand, and a small stature.
• Intellectual Development: Individuals with Down syndrome typically experience some degree of intellectual disability, ranging from mild to moderate. This can affect learning abilities, problem-solving skills, and cognitive processing.
• Potential Health Challenges: The extra chromosome can also affect the development of various organ systems, increasing the likelihood of certain health conditions. These may include congenital heart defects, gastrointestinal issues, vision and hearing problems, and a higher risk of thyroid conditions.

It's important to note that the extent and severity of these characteristics vary widely among individuals with Down syndrome.

Detecting Down Syndrome During Pregnancy

For expectant parents, understanding if their baby has Down syndrome is often a significant aspect of prenatal care. There are several options available to assess the likelihood of Down syndrome during pregnancy, generally categorized into screening tests and diagnostic tests.

Prenatal Screening Tests

Screening tests are non-invasive and estimate the chance of a baby having Down syndrome. They do not provide a definitive diagnosis but can help parents decide if they want to pursue further testing.

• First Trimester Screening: Combines a blood test (measuring specific hormone levels) with an ultrasound to measure the nuchal translucency (fluid at the back of the baby's neck).
• Second Trimester Screening (Quad Screen): A blood test measuring four different substances in the mother's blood.
• Non-Invasive Prenatal Testing (NIPT): A blood test that analyzes small fragments of the baby's DNA circulating in the mother's blood. This test is highly accurate for detecting Down syndrome but is still considered a screening test.

Diagnostic Tests

Diagnostic tests are invasive but provide a definitive "yes" or "no" answer regarding the presence of Down syndrome. They carry a small risk of miscarriage.

For more detailed information on Down syndrome, including support resources and further explanations, you can visit the Centers for Disease Control and Prevention (CDC) website.