Pregnancy changes nearly everything about an expectant mother’s life. That includes her brain. Pregnancy selectively shrinks gray matter to make a mom’s brain more responsive to her baby, and those changes last for years, scientists report online December 19 in Nature Neuroscience.
“This study, coupled with others, suggests that a woman’s reproductive history can have long-lasting, possibly permanent changes to her brain health,” says neuroscientist Liisa Galea of the University of British Columbia in Vancouver, who was not involved in the study.
Researchers performed detailed anatomy scans of the brains of 25 women who wanted to get pregnant with their first child. More scans were performed about two months after the women gave birth. Pregnancy left signatures so strong that researchers could predict whether women had been pregnant based on the changes in their brains.
The women who had carried a child and given birth had less gray matter in certain regions of their brains compared with 20 women who had not been pregnant, 19 first-time fathers and 17 childless men. These changes were still evident two years after pregnancy.
A shrinking brain sounds bad, but “reductions in gray matter are not necessarily a bad thing,” says study coauthor Elseline Hoekzema, a neuroscientist at Leiden University in the Netherlands. A similar reduction happens during adolescence, a refinement that is “essential for a normal cognitive and emotional development,” says Hoekzema, who, along with colleagues, did most of the work at Universitat Autònoma de Barcelona. Following those important teenage years, pregnancy could be thought of almost as a second stage of brain maturing, she says.
Further experiments suggested that pregnancy sculpts the brains of mothers in a very specific way, making women more responsive to their helpless infants. The regions that shrunk the most — parts of the frontal and temporal cortices as well as the midline — are thought to be involved in taking other people’s mental perspectives. Such selective shrinkage may indicate that these regions become more specialized as a result of pregnancy, an efficiency that may help a new mother better care for a baby.
Brain regions that changed the most also showed large responses to pictures of the women’s infants. What’s more, women whose brains changed the most scored higher on a questionnaire about their attachment to their baby.
First-time fathers showed no such brain changes, a result that suggests the effects on mothers’ brains are not caused by the seismic social upheaval of becoming a parent. “It’s not just having a baby to look after that makes the changes in the brain,” says neuroendocrinologist John Russell of the University of Edinburgh, who didn’t participate in the research.
Instead, the brain changes may be caused by pregnancy hormones such as estrogen and progesterone. “Pregnancy is a time of exposure to massive amounts of hormones that get into the brain,” Russell says. But he points out that because the study didn’t actually study brains during pregnancy, just before and after, “we don’t actually know when this change is coming on.” The extreme hormonal drop that comes during birth may also reshape the brain.