The earliest thumb suckers caught on camera

This 32-week-old fetus’ mouth opens in anticipation of a touch, a purposeful movement that may form the basis of feeding behavior later.

Nadja Reissland

Like lots of parents in the digital age, my phone’s memory is maxed out with pictures of my daughter. I find it almost impossible to resist snapping photos of little Baby V as she goes about her business. She eats avocado! She sleeps in her crib! She holds a giant wooden spoon!  Click, click and click.

But before she was able to dazzle me in person, Baby V’s business was much more mysterious. Aside from some very aggressive late night acrobatics, I didn’t have a clue about what was going on with her. That’s why I treasured her sonogram picture — a tiny snapshot that offered a rare glimpse of her life in utero. I studied that grainy, blurred, black and white image and imagined who that little person was going to be.

Now a hot-of-the-presses Developmental Psychobiology paper demystifies a little part of the hidden lives of fetuses, and suggests that these little guys are a little savvier than we thought.

Scientists have known for a while that fetuses react to touches. After a hand swipes the face, the mouth reflexively moves, for instance. But the new study shows that fetuses are smart enough to actually predict when their little hands start to travel toward the mouth.

Scientists led by Nadja Reissland of Durham University in England took ultrasound videos of fetuses mainly in the third trimester of women’s pregnancies. The researchers then counted the times a fetus opened its mouth before a hand reached its face. As fetuses got older, they were more likely to prepare for the incoming fingers by opening their mouths, the team found. Meanwhile, purely reactive touching — the hand hitting the mouth before the mouth moves — happened less often. Purposeful hand-to-mouth movement probably reflects a high level of sophistication, the researchers say.

Besides offering a thrilling sneak peek of early behavior, this study helps scientists understand how fetuses prep for life as a baby. This newly uncovered trick might help later on with things like feeding and thumb-sucking.

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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