A second pregnancy changes the brain in a different way from the first, new research suggests

A woman’s brain changes in very different ways during her second pregnancy compared with her first, helping her adjust to the demands of raising a larger family.The discovery comes from a study by researchers at Amsterdam University Medical Center, published in the journal Nature Communications. Scientists already knew that a first pregnancy causes structural changes in the brain. This new study shows that later pregnancies do not simply repeat those changes. Instead, each pregnancy leaves its own unique mark on the mother’s brain.The team followed 110 women, taking brain scans before conception and again after childbirth. Some women were pregnant for the first time, some were expecting their second child, and a control group remained childless. By comparing the groups, the researchers identified the exact physical changes that happen when a woman becomes a mother for the second time.

Shifting focus from inward to outward

During a first pregnancy, the biggest changes happen in the brain’s default mode network. This network is responsible for self-reflection, daydreaming and understanding social situations.During a second pregnancy, this network changes again, but much less than the first time. Instead, the biggest changes happen in areas of the brain that control attention and process physical sensations, helping mothers focus more on the outside world.“It appears that during a second pregnancy, the brain is more strongly altered in networks involved in reacting to sensory cues and in controlling your attention,” said Milou Straathof, a researcher who analysed the study data. “These processes may be beneficial when caring for multiple children.”The physical changes included reductions in grey matter volume, surface area and cortical thickness in certain parts of the brain. In second-time mothers, the average reduction in these areas was 2.8 per cent. First-time mothers experienced a slightly larger reduction of 3.1 per cent across a brain region that was 79 per cent larger than the one affected in second-time mothers.Using advanced computer analysis, the researchers looked only at these brain changes and were able to correctly identify whether a woman had completed her first or second pregnancy with 80 per cent accuracy.The scans also showed that although the brain started to recover during the later months after birth, it never returned to its original state before pregnancy in either group. The amount of time since a woman’s first birth also did not affect the brain changes seen during her second pregnancy.

Tracking bonding and depression

The researchers also compared these brain changes with the mothers’ emotional experiences. They found a clear link between the physical changes in the brain and how strongly a mother bonded with her baby.This connection was much stronger after a first pregnancy than after a second. For first-time mothers, the brain changes closely matched their early feelings of attachment to both the unborn baby and the newborn. For second-time mothers, the same connection was still present but involved fewer brain regions.The study also provides the first direct evidence that changes in the brain’s outer layer are linked to peripartum depression. However, the timing of this risk depends on whether it is a woman’s first or second pregnancy.For first-time mothers, the strongest link between brain changes and depressive symptoms appeared after childbirth. For women having a second baby, the connection appeared much earlier, while they were still pregnant. In both groups, women whose brains showed fewer changes reported higher levels of depression and emotional distress.“With this, we have shown for the first time that the brain not only changes during the first pregnancy, but also during a second,” said Elseline Hoekzema, head of the Pregnancy Brain Lab at Amsterdam UMC. “During a first and second pregnancy, the brain changes in both similar and unique ways. Each pregnancy leaves a unique mark on the female brain.”

Long-term health implications

For many years, scientists have known very little about how repeated pregnancies affect the human body over a lifetime. Earlier studies in animals showed that rodents experience lasting changes in brain structure and hormone activity depending on how many litters they have, but similar evidence in humans has been limited.By showing that the human brain continues to reshape itself during later pregnancies, the Amsterdam UMC study fills an important gap in women’s health research. The researchers say the findings highlight the brain’s ability to adapt during major life changes.“This knowledge can help to better understand and recognize mental health problems in mothers,” Hoekzema said. “It is important that we understand how the brain adapts to motherhood.”The team hopes these findings will help doctors better predict, identify and treat mental health problems in mothers. Knowing that second-time mothers experience important brain changes earlier in pregnancy could change how doctors screen for anxiety and depression before birth.The findings may also help explain why previous international studies have linked multiple pregnancies with a younger biological brain age and different risks of neurological diseases later in life. Because the brain’s attention and sensory networks become more active during a second pregnancy, these changes may help protect the brain as women grow older.