What is Really Going On in There?

Dear Mr. Dad: Please settle an argument. My wife—who’s five months pregnant—says that our baby’s senses are developing throughout the pregnancy. I think she’s crazy. How can an unborn baby develop a sense of touch or taste or anything else?

A: This round goes to your wife. Your baby will be born with a full set of senses: touch, hearing, sight, smell, and taste. But they don’t just show up at birth, completely out of the blue. They begin forming very early on in the pregnancy and the fetus starts trying to use them immediately. The more practice she gets, the more developed the sense will be at birth. (Senses that aren’t used tend to atrophy. In animal experiments, for example, when fetal chicks are prevented from moving inside their egg, cartilage turns to bone). In previous columns, we’ve talked about what babies hear before they’re born. Here’s an introduction to the rest of the senses.

  • Touch. About two months into the pregnancy, your baby’s skin—her body’s largest organ—is fully formed. Sensitivity starts with the cheeks and lips, and just a few months ago, if they were touched, the baby would turn away. Starting at about five months, the baby will turn towards the touch (after birth, that’s called the rooting reflex, and it’s designed to help the baby find the breast). The palms of the hands, soles of the feet, and genitals are next. To help develop their sense of touch, fetuses spend a lot of time exploring themselves—grasping the umbilical cord, stroking the face, sucking on fingers, and kicking and banging against the walls of the uterus. If the baby has a womb-mate or two, the occupants often explore each other.
  • Smell and taste (sometimes lumped together as “chemosensation”). Your baby’s mouth and tongue developed a few months ago. And at this stage, her taste buds are just about as sensitive as yours. For the past month or two, she’s been gulping down impressive amounts of amniotic fluid, peeing it right back out, and drinking it up again (it’s best to get that image out of your mind). The amniotic fluid that flows through her mouth and nasal passages changes flavor constantly, depending on what your partner eats. (Researchers have found that adults were able to smell garlic in amniotic fluid collected from women undergoing amniocentesis who had eaten garlic just 45 minutes before the test.) But mixed in there among the curry and chili peppers and PB&J sandwiches are some odor molecules that are distinctly Mom. After birth, the baby’s sense of smell helps her adjust to life outside the womb. Mom’s nipples smell (to the baby) like amniotic fluid, and that scent helps attract the baby to the breast. Babies definitely prefer the smell of their own fluid to anyone else’s (who wouldn’t?).
  • Sight. Your baby’s eyes will be fused shut for another month or two. Even after they open, it’ll still be pretty dark inside Mom. Nevertheless, she’s doing some visual processing. For example, if you were to shine a bright light on your partner’s belly (which you shouldn’t do), your baby’s heart rate would accelerate and she’d turn away from it. Because of the lack of practice, eyesight will be your baby’s least-developed sense when she emerges from the womb. At first, things will be a little blurry, although she’ll be able to see objects—or people—10 to 15 inches away fairly well. But in six to nine months, her eyesight will be pretty much up to snuff.