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A Tour of Your Baby's Developing Body

Have you ever wondered how well a newborn baby can hear or see? Take this tour of the baby body and find out how a little one develops.

By Wyatt Myers

Medically reviewed by Pat F. Bass III, MD, MPH

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All parents want their newborn baby to be healthy and perfect. So it’s not surprising that new parents have a lot of questions when it comes to their baby’s developing body.

While it’s true to some degree that a baby is like a miniature version of mom and dad, newborns may experience the world quite differently than an adult does. A lot of the senses and body functions aren’t fully formed when a baby is born, and it takes time for these abilities to develop.
The easiest way to make sense of what a newborn experiences is with a tour of the developing body, starting with the head. We recruited two top pediatricians to serve as tour guides to baby development.
The Newborn Baby’s Head
Looking at your baby’s head, you’ll probably want to make sure those little ears and eyes are working right. Johnnie P. Frazier, MD, associate professor of pediatrics at the University of Texas Health Science Center at Houston, says that babies can actually hear fairly well when they’re born. “Hearing tests are done at birth to assure this function,” Dr. Frazier says.
A baby’s eyes, however, take a little time to adjust to their new surroundings. “Newborns can only focus 8 to 10 inches in front of them,” Frazier says. “They like to focus on the human face, and prefer simple black and white images to more complex images. Primary colors become more stimulating about two months later.”
You’ll also notice when looking at your newborn baby that the skull isn’t fully formed. “The fontanel, which is the soft spot on the top of a newborn's head, is present until a baby is 9 months to 2 years of age,” says Hannah Chow-Johnson, MD, assistant professor in the department of pediatrics at Loyola University Medical Center in Chicago. “There’s a smaller soft spot on the back of the head that closes by age 6 months.”
New parents may also wonder when their baby will start getting teeth. While babies are born without visible teeth, the development of baby teeth begins in the womb. The basic structure of the teeth and the hard tissue around each tooth is formed by 3 or 4 months of fetal development. A baby’s first tooth (bottom front incisor) will likely make an appearance through the gums at around 7 or 8 months of age. The top front incisors should follow about a month or two later.
The Newborn Baby’s Body
Many of the bones in a baby’s body are primarily made up of cartilage at birth. This makes them flexible yet very strong. But don’t be surprised if your baby looks curled up. “Infants look like little frogs when they’re born, keeping their arms, legs, and hips flexed,” Dr. Chow-Johnson says. “As they mature neurologically, they’ll start relaxing their arms and legs, which become more extended.”
Another common question parents have is about a baby’s skin. “Parents may be concerned with their newborn’s skin peeling or feeling dry,” Frazier says. “Physicians reassure parents that this is normal and no additional oil is necessary.” A small amount of water-based lotion, such as Lubriderm or Eucerin, is fine, she adds.
You may notice a spot in the middle of baby’s chest called the xiphoid process. “This looks like a small bump in the middle of the chest and is an extension of the sternum,” Chow-Johnson says. “This is normal, but it looks more prominent in infants.”
The Newborn Baby’s Immune System
Most newborn babies are born with a functional immune system, however it’s not fully developed. “The immune system is partially protected by the transfer of maternal immunoglobulins into a newborn’s circulation until approximately 6 months of age,” Frazier says. But a baby’s immunity system has yet to build up antibodies from a lifetime of exposure to germs, so great care must be taken to prevent your newborn from becoming sick. “Parents, other caregivers, family, and friends will need to be careful to wash their hands before handling a newborn and should avoid contact if sick,” says Frazier. “Newborns don’t localize infection as well as older infants, so taking precautions to protect them from possible infections is important.”
Baby Development Signs to Look For
A newborn baby’s body moves and reacts differently than that of older children, and newborns have some reflexes that older children don’t have. Chow-Johnson shares some reflexes you may see in your newborn baby:

• Startle reflex. The arms and legs extend completely, usually in response to sudden movement or sound.
• Asymmetrical tonic neck. This is also called the fencer's reflex. If you move a baby’s head to one side, the arm it’s facing will extend while the other arm flexes, so the baby will look like it’s fencing.
• Babinski reflex. This happens when you tickle an infant’s foot in an upward motion, causing the toes to fan out.

“All of these reflexes normally disappear by age 4 to 6 months,” Chow-Johnson says.
Other early signs of baby development to look for include smiling, making speech sounds, and starting to lift up the head. These all happen at about 1 month. By 2 months, a baby will make more extended sounds and begin to get better at tracking you with its eyes. By 4 months, look for rolling, cooing, and laughing.
As a new parent, you’ll watch your baby’s body move and change with delight. If you have any questions or concerns about baby development, be sure to talk with your baby’s doctor.