How a Doctor Diagnoses Down Syndrome

A pediatrician is often the first to suspect Down syndrome in a newborn. The diagnosis is usually considered when a baby has certain physical findings, facial features, and possibly other birth defects.

This guide will explain what your pediatrician is looking for and what tests are necessary to diagnose Down syndrome in a newborn baby.

It is important to remember that while there are some similar findings that lead to a diagnosis of Down syndrome, no single baby with Down syndrome will have all of the features described here. Nor does the number of physical problems in a baby with Down syndrome correlate with their intellectual capacity. Just like all other children, each and every child with Down syndrome has his or her own unique personality and strengths.

Hypotonia in Down Syndrome

One of the most common symptoms of Down syndrome is hypotonia or low muscle tone. Almost all babies with Down syndrome have hypotonia and appear "floppy" at birth. Hypotonia generally improves over time, and most children with Down syndrome will have physical therapy in infancy and childhood to help improve their hypotonia.

Facial Features in Down Syndrome

A baby with Down syndrome has some distinct facial features, which can include almond-shaped eyes (due to epicanthic folds); light-colored spots in their eyes (called Brushfield spots); a small, somewhat flat nose; a small mouth with a protruding tongue; and small ears. They also have round faces and somewhat flatter profiles.

None of these facial or physical features are abnormal by themselves, nor would they cause a baby with Down syndrome any medical problems. But if a doctor sees a number of these features together in one baby, they may begin to suspect that the baby has Down syndrome. These facial and physical features are what cause people with Down syndrome to resemble one another, although they also resemble their own families.

Single Palmar Crease of the Hands in Down syndrome

Another physical feature seen in infants with Down syndrome is a single crease across the palms of their hands. This doesn't cause them any problems—their hands will work fine—but it is a sign that your pediatrician will be looking for if he suspects that your baby has Down syndrome. Other hand differences sometimes seen in infants with Down syndrome include short, stubby fingers and a fifth finger or pinky that curves inward, a condition called clinodactyly.

Heart Defects in Down Syndrome

About 50 percent of babies with Down syndrome are born with heart defects, which is a much higher percentage compared to the number of children without Down syndrome who are born with heart defects (approximately 1 percent). The most common heart defect seen in infants with Down syndrome is an atrioventricular septal defect or AV canal. Other heart defects seen in infants with Down syndrome include ventricular septal defects (VSD), atrial septal defects (ASD), and patent ductus arteriosus (PDA).

If your baby is found to have a heart defect, you will be referred to a pediatric cardiologist to discuss treatment options, which often include corrective surgery and medication.

Intestinal Defects in Down Syndrome

About 10 percent of infants with Down syndrome will have gastrointestinal issues, such as a narrowing or blockage of the intestines (duodenal atresia), an absent anal opening (anal atresia), an obstruction of the outlet of the stomach (pyloric stenosis), or an absence of the nerves in the colon, called Hirschsprung’s disease. Most of these malformations can be fixed with surgery.

Hypothyroidism and Down Syndrome

People with Down syndrome can also have problems with their thyroid gland, which is a small gland located in the neck. People with Down syndrome may not produce enough thyroid hormone, a condition called hypothyroidism. Hypothyroidism is most often treated by taking replacement thyroid hormone for the rest of the person’s life.

Ordering a Karyotype to Diagnose Down Syndrome

Karyotype showing the arrangement of chromosomes in a female with Downs syndrome (trisomy-21)
Karyotype showing the arrangement of chromosomes in a female with Downs syndrome (trisomy-21). Getty Images/KATERYNA KON/SCIENCE PHOTO LIBRARY

If your pediatrician is concerned that your baby may have Down syndrome, he or she will order a karyotype, or chromosome analysis, to be done. A karyotype is a blood test that looks at a person's chromosomes. It typically takes between two to five days to get the results of a karyotype test.

Karyotype Results Confirm the Diagnosis of Down syndrome

Karyotype showing trisomy 21
Karyotype showing trisomy 21. K. Fergus

The karyotype, or chromosome analysis, reveals the number of chromosomes that a baby has, as well as the chromosomes' structure. Most babies with Down syndrome have an extra number 21 chromosome—a condition called trisomy 21. Because of this extra chromosome, they have 47 chromosomes instead of the usual 46.

Occasionally a baby's chromosomes will be rearranged, which is called a translocation. If a baby is found to have translocation Down syndrome, his or her parents should also have a karyotype test to determine if they are a carrier of this translocation.

Another type of Down syndrome that can be detected by karyotype is called mosaic Down syndrome, in which the baby has two cell lines—one with normal chromosomes and one with trisomy 21.

Coping With the Diagnosis of Down syndrome

Taken by 56grad Germany/Moment/Getty Images

Learning that your child has Down syndrome can be a very confusing time in your life. You may feel overwhelmed, afraid, and alone. There are some things that you can do to help yourself through the first few days, including allowing yourself to grieve and asking for help.

Remember that there is a team of people available to help. Your family and friends will take their cue from you, so be sure and tell them what they can do to help.

If your child has other medical needs, meet with their doctor and ask questions. Most importantly, be sure and spend time with your baby.