In the third trimester, a pregnant woman’s sense of personal space grows

Lots of changes come with pregnancy, but perhaps none is as obvious as the ever-growing midsection. Pregnant women’s bodies accommodate their babies in many ways — rib cages stretch, lungs bunch up around the throat and belly buttons pop out — as the fetus takes over every possible centimeter of available real estate.

Along with that physical expansion comes an interesting mental one: Late in pregnancy, women’s sense of personal space grows too, a preliminary study finds. Pregnant women’s peripersonal space — the personal bubble defined as her own — expands during the third trimester, Flavia Cardini of Anglia Ruskin University in Cambridge, England, and colleagues reported December 10 at bioRxiv.org.

To define the boundaries of peripersonal space, the researchers asked blindfolded participants to push a button as soon as they felt a light tap on the abdomen. Their responses could be tweaked with another signal: a 3-second-long sound that seemed to start far away and then move closer.

People are slower to respond to a tap given while the sound is far away. But like a Karate-Kid chopstick to a fly, people’s reaction times to the tap sped up when the sound seemed closer, earlier studies have found.

By pinpointing the distance at which reaction times sped up, Cardini and her colleagues could draw the peripersonal space boundaries of women at three stages of pregnancy: At week 20, when many women are just beginning to grow larger; at week 34, when they’re quite large; and about 2 months after giving birth. For comparison, researchers also tested women who hadn’t been recently pregnant.

Compared with these women, women who were 34 weeks pregnant were quicker to push the button in response to a tap when the accompanying sound was farther away, results that suggest that in the third trimester, women’s senses of personal space expands. There were no effects when the women were 20 weeks pregnant, or after the women had already given birth.

Some psychologists think of the peripersonal space as a protective bubble that wraps around the body. Studies of barking dogs, spiders and snakes suggest that the peripersonal space can expand when faced with threats. The expansion of peripersonal space “might be aimed at protecting the vulnerable abdomen — and the new entity held within it — during the mother’s daily interaction with the external environment,” the researchers write.

Cardini was surprised to find this expansion only late in pregnancy. “I would have expected something happening early in pregnancy as well,” she says. But perhaps earlier stages of pregnancy don’t require extra monitoring, she says.

The idea that all sorts of things expand during pregnancy, and later, during parenthood, resonates with me. It seems almost as if our very sense of self grows larger, making room for these new, vulnerable people and adding them to the fold.

Another implication of this research occurs to me, and it has to do with unwelcome belly pats. This should go without saying, but I’ll say it anyway: It’s never, ever a good idea to touch someone’s midsection without asking. Still, if you must, be forewarned: Armed with a big peripersonal space, a woman in her third trimester will be much quicker at swatting hands away.