Babies with Down syndrome share a recognizable set of physical features, though no two children look exactly alike. The most common visible trait, present in about 90% of newborns, is a flat facial profile. Other features involve the eyes, ears, hands, and overall muscle tone, and they range from very subtle to quite noticeable depending on the child.
Not every baby with Down syndrome will have every feature listed below. Some children have only a few, while others have many. The type of Down syndrome also matters: babies with the mosaic form, where only some cells carry the extra chromosome, often have milder or fewer physical characteristics.
Face and Head Shape
The face tends to look flatter than average, especially across the bridge of the nose. The nasal bridge sits lower, giving the mid-face a less projected appearance. Newborns often have a round face and a head that is slightly shorter from front to back, sometimes described as a “flattened” back of the head. Loose folds of skin at the back of the neck are visible in roughly 80% of newborns with Down syndrome, though these typically become less noticeable as the baby grows.
The neck itself is often short and broad. The mouth may appear small relative to the tongue, which can cause the tongue to rest forward or protrude slightly. This isn’t always because the tongue is unusually large. In many cases it’s a combination of a smaller oral cavity and lower muscle tone in the face and jaw. The roof of the mouth is often high and narrow.
Eyes
The eyes are one of the most recognizable features. The outer corners slant gently upward, a trait present in about 80% of newborns. Small folds of skin at the inner corners of the eyes, called epicanthal folds, can make the eyes appear wider set than they are. These folds are also common in many children without Down syndrome, particularly in certain ethnic backgrounds, so on their own they aren’t diagnostic.
Some babies also have small, light-colored speckles on the iris, visible as pale spots arranged in a ring. These are harmless and don’t affect vision. They show up more often in babies with lighter-colored eyes. Studies have found them in anywhere from 17% to 81% of children with Down syndrome depending on the population studied, and they’re rarely seen in children with dark brown eyes.
Ears
The ears are typically small and round, sometimes sitting slightly lower on the head than usual. About 60% of newborns with Down syndrome have ears that look simpler in shape, with less of the folded cartilage detail you’d see in a typical ear. The ear canals can also be narrower, which is relevant later for hearing screening.
Hands and Feet
The hands tend to be broad and short, with shorter fingers. The pinky finger sometimes curves inward slightly, and on X-ray, the middle bone of the pinky is often underdeveloped (seen in about 60% of newborns). One of the more well-known markers is a single crease running straight across the palm instead of the typical two curved lines. This appears in roughly 45% of babies with Down syndrome, making it common but far from universal. It can also appear in people without any chromosomal condition.
On the feet, there is often a wider-than-usual gap between the big toe and the second toe, sometimes called a “sandal gap.” This is easy to spot and is one of the features clinicians look for during a newborn exam.
Muscle Tone and How the Baby Feels
Low muscle tone, or hypotonia, is present in about 80% of newborns with Down syndrome and is often the very first thing a parent or nurse notices. A baby with low tone feels unusually floppy or limp when picked up. Their arms and legs may hang loosely at their sides rather than staying slightly bent at the elbows and knees, which is the typical newborn posture.
When you hold a baby with low tone under the arms, they may feel like they’re slipping through your hands because their muscles don’t grip the way you’d expect. They often have difficulty holding their head up, and their startle reflex (the sudden arm-flinging motion newborns make in response to loud sounds or being moved quickly) is weaker or absent in about 85% of cases.
Low tone doesn’t mean the muscles are weak, exactly. It means the muscles are more relaxed at rest. With physical therapy and time, babies with Down syndrome build strength, though they typically reach motor milestones like sitting, crawling, and walking later than their peers. Their joints are also more flexible than average, with about 80% of newborns showing noticeably loose or hyperextensible joints.
Size at Birth and Growth
Babies with Down syndrome are generally born at an average or slightly below-average size. Many fall within the normal range for birth weight and length, so size alone won’t signal anything unusual. Over time, though, children with Down syndrome tend to follow a different growth curve. The CDC publishes specific growth charts developed from measurements of children with Down syndrome, tracking weight, length, and head circumference from birth through age three and beyond. Pediatricians use these specialized charts rather than standard ones so that a child’s growth is compared to an appropriate reference group.
How Features Vary
The physical features of Down syndrome exist on a spectrum. A child inherits facial structure, skin color, hair type, and body build from their parents just like any other child, and these family traits blend with the characteristics associated with the extra chromosome. Two babies with Down syndrome from different families can look quite different from each other while still sharing certain recognizable features.
In mosaic Down syndrome, where only a percentage of the body’s cells carry the extra chromosome, features can range from very mild to nearly identical to the standard form. Some children with mosaic Down syndrome have so few visible traits that the condition isn’t suspected until developmental delays or health screenings prompt genetic testing.
It’s also worth knowing that many of these features become more or less prominent with age. The epicanthal folds, for example, often become less noticeable as the bridge of the nose develops during early childhood. Low muscle tone improves with intervention. The overall appearance shifts as the child grows, just as it does for all children.