Why do babies have their fists clenched almost all the time?

shutterstock

Ah, a pediatrician getting to answer a question parents never ask. They never ask because we see it so commonly. It's just what babies do. I've thought about it, and I wonder if it's more important than we think. Could that simple question lead to a more important one?

When I asked that question in medical school on nursery rounds, my professor's answer was "It's the palmar grasp reflex." Hey, I saw what you did; you just put a medical name on my question and repeated it. That's not an answer.

I would never have said that. But I should have said, "OK, so why do newborns have the palmar grasp reflex?" Even today the answers you will get are incomplete: "It is an awkward primitive reflex due to increased cortical neuronal tone, the sign of an immature neurological system, or a vestigial primal remnant for holding onto mom." Do you see what they did?

So state the question a different way,"Why does Mother Nature still think it is important that newborns clench their fists most of the time?"

This whole clenched baby fist may be a lot more interesting than we think

Mother Nature certainly thinks it's important. Not only do newborns clench their fist, but they do it in a distinctly different way than we do. Here is a cute photo someone put on their FaceBook called "Baby's first fist bump":

Do you see it?

Newborns tuck their thumb in. What's that all about? It is awkward; it doesn't feel natural, just try it. So something is up, but it's for when a baby is in the womb; because they stop tucking it in just after they are born. There are even medical articles about the weird TIF, "thumb in fist," eventually concluding "it is probably of minimal clinical importance."

Well, Mother Nature doesn't do things for no reason. What if it is of clinical significance? Here is one way to get at the answer:

So what would happen if they didn't?

It's not hard to imagine all kinds of havoc that open groping hands could do in the womb. But why tuck the thumb in? A thumb couldn't do much grabbing and pinching with the fingers tucked in. Maybe it's not about the fingers per se, but something related to them.

Speaking of havoc, the most delicate area in the womb is not the baby; it's that remarkable thin amniotic sac that envelops the baby. The amnion is a complex nurturing biochemical membrane. Even scratching or pricking that amnion can induce a cascade of chemicals and hormones and lead to premature labor. During amniocentesis, doctors routinely caution parents that even the stick of the needle can induce premature labor. When doctors need to induce labor, they will just strip a small part of the amnion to get the process going.

Do not mess with the amniotic sac

So maybe it's not grasping fingers that Mother Nature worries about. What about fingernails? Even though prenatal fingernails are very soft, Mother Nature may want them tucked in to prevent damaging that amnion. With that odd thumb-in-fist, Mother Nature gets all the nails out of the way.

My professor would think this was far fetched, and he would quickly ask "What about the toenails? Babies can't ball up their toes." Babies kick all the time in utero, so that is a good question, and I think the answer is fascinating.

It is interesting to note that although parents frequently ask how to trim their newborn's fingernails, they never ask how to trim newborn toenails. You see, newborns don't have toenails that stick out like fingernails. Mother Nature covers over the tips of newborn's toenails. Of course, doctors have noticed this, but sort of regard it as Mother Nature's mistake, missing the point:

Whatever Mother Nature's wisdom is that babies be born with long scratchy fingernails, she never has them born with long toenails. Mother Nature knows a baby can't ball up their toes like a fist, so she buries the ends of toenails into thick layers of skin, out of harm's way. Enough that doctors write articles about it. They can kick all they want inside the womb; nothing's getting scratched. Mother Nature has it covered.

Again: So what would happen if they did not clench their fists?

They might injure the amniotic sac. We've already noted that's not a good thing, but as a pediatrician it makes me wonder about something else. There is an unfortunate and not uncommon congenital disability called amniotic band syndrome. I realize this sounds awful, but if you have ever seen a child missing fingers, hands, or part of a leg, it is a common cause. The accepted thought is that for some reason fine strands of the amniotic sac are peeled away and float around the amniotic fluid with the baby. The strands wrap around fingers, toes, even arms and cause them to amputate, often in multiple places.

"...of no clinical importance."

While these wrapping bands are the currently accepted cause, no one has ever figured out why sometimes tiny bands of amniotic sac get stripped away from the inside, in utero. The reason I am glad you asked about babies clenching their fists, is because just thinking about why Mother Nature does simple things can lead to new ways of thinking. For example, I would like to see if newborns with amniotic band syndrome lack a proper "palmar grasp reflex." Or do they not have "hypertrophy of the toenail folds," leaving those little nails to peel off amnion? Now that's another good question, but maybe for a medical journal.