Getting to Know You

Baby's Developing Senses
By Karin A. Bilich

How baby learns to see, hear, smell, touch, and taste.

Shortly after your baby is conceived, she seems to be just a tiny little tadpole. But nine months later, she's a real person with five acute senses. How do those senses develop? Read on and find out.

Touch

Just before the eighth week of gestation, an embryo develops its first sensitivity to touch. The first parts of its body to experience sensitivity are the ones that are the most sensitive in adults. It starts in the cheek and then quickly extends to the genital area (10 weeks), palms (11 weeks), and soles of the feet (12 weeks). By 17 weeks, the abdomen and buttocks are also sensitive. Your baby may experiment with this newfound sense of touch by stroking his or her face or sucking on a thumb, as well as feeling other body parts and seeing how they move.

By 32 weeks, nearly every part of the body is sensitive to heat, cold, pressure, and pain.

Taste

By 13 to 15 weeks a fetus's taste buds already look like a mature adult's, and the amniotic fluid that surrounds the fetus can smell strongly of curry, cumin, garlic, onion, or other strong tastes from a mother's diet. Studies show that a fetus's swallowing increases when surrounded by sweet tastes and decreases with bitter and sour tastes.

During the last trimester, the fetus is swallowing up to a liter a day of amniotic fluid, which may serve as a "flavor bridge" to breast milk, which also carries food flavors from the mother's diet.

By birth, babies have a strong sense of taste. Newborns can discriminate between tastes and have shown definite taste preferences. Even preemies as young as 33 weeks suck harder on a sweetened nipple than on a plain rubber one.

Smell

A fetus's nose develops between 11 and 15 weeks. Until recently, scientists didn't believe that fetuses would have any sense of smell, since it was assumed that smelling depended on air and breathing. However, the latest research has opened up a new world of possibilities.

The nasal system is made up of no less than four subsystems, and it's now believed that the amniotic fluid surrounding the fetus passes through the baby's oral and nasal cavities, triggering these senses.

Studies have shown that newborns are drawn to the odor of breast milk, although they have no previous experience with it. Researchers think this may come from cues they have learned in prenatal life.

Hearing

The womb is not a silent place. There's blood whooshing through the mother's vessels, gurgling and rumbling from her stomach and intestines, and the tones of her voice and the voices of others.

A baby's ears begin to form at around eight weeks and become structurally complete at about 24 weeks. But as early as 18 weeks, the bones of the inner ear and the nerve endings from the brain have developed enough for your baby to hear sounds such as your heartbeat and blood moving through the umbilical cord. He may even be startled by loud noises! For the rest of the pregnancy, sound serves as a baby's major information channel. By week 25, your baby begins to hear your voice--and your partner's--and may even recognize those voices as early as week 27. Sounds may be muffled, though, because the ears are still covered with vernix, the thick, sticky coating that protects the skin from becoming chapped by the amniotic fluid.

A fetus's movements or body patterns may change in response to sounds. Many pregnant women report a fetal jerk or sudden kick just after a door slams or a car backfires. A baby's heart rate often slows down when its mother is speaking, suggesting that he not only hears and recognizes the sound, but is calmed by it.

Sight

Vision is the last sense to develop. In utero, eyelids remain closed until about the 26th week in order for the retinas to fully develop. Around week 26, the eyes open and even begin to blink! At birth, a baby's vision is perfectly focused from 8 to 12 inches.

As soon as their eyes open in the womb, twins seem to have no trouble locating each other and touching faces or holding hands.

Just as the womb isn't completely quiet, it isn't totally dark, either. As early as week 18, when the eyes are still closed, a baby's retinas can detect a small amount of light filtering through a mother's tissue if she's out in the bright sun or under strong lights. By week 33, the pupils of the eye can now detect light and constrict and dilate, allowing your baby to see dim shapes. Studies shining a bright light on the belly of a woman at 37 weeks have shown a baby's heart rate speeding up in response, or the baby turning toward the light. (Note: Exposing a fetus or premature infant to bright light before it's ready can damage.