Crick scientists have found that in some species, pregnancy causes a permanent lengthening of the small intestine.
Bodies change in remarkable ways during pregnancy. Many of these changes have long been known, if not fully understood, such as increased blood volume, changes to kidney function and joint alterations. Now, new research is suggesting that in some species, the gut also undergoes profound and seemingly permanent changes during pregnancy.
Irene Miguel-Aliaga, who leads the Crick’s Organ Development and Physiology Lab, first made this surprise discovery when researchers in her lab noticed that female fruit flies had longer guts than their male counterparts, and they became even longer after reproducing.
“We weren’t looking specifically for pregnancy‑related changes, we just happened to stumble upon them while examining male and female fruit flies,” says Irene.
To see if this occurred in other species, Irene’s team studied pregnant mice and found that their small intestine began to lengthen just seven days into pregnancy – and by the time they gave birth it was around 18% longer. They also found that structures on the gut wall that absorb nutrients, called villi, grew longer and deeper.
The gut epithelium of non-pregnant (top), pregnant (middle) and lactating (bottom) mice, showing how the villi on the surface of the gut wall grow longer and deeper during pregnancy.
What’s more, says Irene’s colleague Tomotsune Ameku, the change was permanent. “The mice retained longer guts after they had finished lactating, and their small intestine grew even longer after a second pregnancy.”
The idea that such changes occur in adulthood, rather than earlier in life, isn’t usually considered, says Irene. “But the gut is a striking example of how the body responds to a new challenge at different stages of life, in this case pregnancy.”
Their discovery overturns long‑held assumptions about maternal biology and, if shown to occur in humans, suggests how much there is still to learn about how our bodies change during pregnancy. It also opens up new opportunities for understanding the evolutionary changes that have optimised reproductive success across species.
To explore what happens in our own bodies, Irene’s team has launched a study to scan pregnant women to see if their small intestines grow in the same way. But as Irene explains, humans may not have the same evolutionary demand for energy when pregnant, as we tend to have only one baby at a time.
If the phenomenon does occur in humans, Irene is keen to explore how it might interact with modern life. “We’re generally eating more and having fewer children than we used to, so if our intestines do grow, it might not be as useful an adaption for us anymore,” she says.
