Scientists say pregnancy changes women’s brains

For the first time, scientists have found evidence of specific and long-lasting changes in the brains of pregnant women. The changes were measured in brain areas that are responsible for social cognition and the ability to understand the thoughts and intentions of others, suggesting that they may intensify maternal bonding with a newborn.

The neuroimaging study, conducted in Spain, looked at the brains of 25 first-time mothers before and after pregnancy, and again two years after the women gave birth. The researchers compared the brain images of these new mothers to those of 19 first-time fathers, as well as 17 men and 20 women without children. The pattern of structural changes in the new mothers were so distinct that it was possible to identify the mothers just from their brain scans. Those changes endured for at least two years, except for a partial return to the previous state in the hippocampus, a brain structure involved with memory.

The MRI study showed changes in gray matter, the outer layer of the brain that contains the cell bodies of neurons. The gray matter in certain areas shrank after pregnancy. Similar shrinkage is seen in early childhood and during adolescence. During pruning, the most important connections among neurons are strengthened and the others are left to wither. Pruning is generally taken to mean that a brain region has become more specialized.

The researchers found that some women had more gray matter pruning than others, and those with the most pruning seemed to bond best with their babies. “The gray matter volume changes of pregnancy significantly predicted the quality of motherto-infant attachment and the absence of hostility toward their newborns in the postpartum period,” the authors wrote in an study published Monday in Nature Neuroscience.

The researchers showed women pictures of several babies and found that the women’s brains responded more strongly to photos of their own babies. The brain images, they said, revealed “the strongest neural activity in response to the women’s babies corresponded to regions that lost gray matter volume across pregnancy.”

Pregnancy is associated with a surge of sex hormones akin to the heightened production of sex hormones during puberty. The researchers noted that gray matter also is pruned during adolescence, when a spectrum of emotional, cognitive and behavioral neural changes begin to fine-tune the teenage brain.

Cordelia Fine, a psychologist at the University of Melbourne who had no part in this research, cautions that the brain areas identified by the scientists are also responsible for other functions, not simply attachment. A more significant caveat, she said, is that while the authors of the study “speculate that the structural brain changes they see underlie maturation” of neural networks that “could facilitate attachment ... it’s worth noting that the authors measured empathy before and after pregnancy, and found no change.”

According to the authors of the study, these brain changes may “serve an adaptive purpose for pending motherhood” — that is, the stronger the mother-child attachment, the greater chance the child survives.

Women with more gray matter pruning during pregnancy bond best with their babies, a new study suggests.