Doctor’s Note: Pregnancy Brain

In a recent neuroanatomy study published in Nature Neuroscience, University of California Irvine neurobiologist Dr. Liz Chrastil underwent 26 brain MRI scans before, during, and after her pregnancy. This study is unique due to the large number of scans on a single subject. Older studies typically only did a few MRIs per subject, whereas this study obtained multiple scans before conception, during all three trimesters of pregnancy, and up to two years after childbirth. This allowed researchers to make detailed comparisons between timepoints and also correlate with estrogen and progesterone levels seen on bloodwork.

So, what did the study find? First, let’s explain the types of measurements they took. The researchers used MRI to measure the volume of gray and white matter, as well as the white matter microstructural integrity, across dozens of regions throughout the brain. Gray matter contains neuron cell bodies whereas white matter contains nerve tracts. You can think of them as being like circuit boards and wires, respectively. White matter integrity is a measure of how easily fluid moves along white matter tracts. Gray matter volume and white matter integrity don’t always correlate with cognitive performance, just as stuffing more parts into a computer doesn’t guarantee it will run faster. But large changes in brain anatomy indicate the presence of an underlying biological process, such as brain maturation in adolescence, or neurodegenerative disorders later in life.

The Nature Neuroscience study showed rapid structural changes during pregnancy in multiple areas throughout the brain, far exceeding the day-to-day brain changes in non-pregnant controls. There were large decreases in gray matter volume (GMV) across most of the brain, with an average of -4 percent GMV by the end of pregnancy. These changes partially reversed after childbirth, but GMV remained lower than baseline at two years afterward, affecting the vast majority of the brain. The only region that increased in volume during and after pregnancy was the limbic system, which is linked to emotion, motivation, memory, and behavior. At the same time, there were large increases in white matter microstructural integrity early in pregnancy, which reverted back to normal shortly after childbirth.

What does this mean? Are pregnancy-related reductions in gray matter volume a bad thing? Could they be the cause of “mommy brain,” postpartum depression, or other maladies? Well, Dr. Chrastil said that she did not experience “mommy brain” or any other complications. Decreasing the volume of gray matter doesn’t mean decreasing neurocognitive function — similar volume reductions occur during normal puberty. It’s believed that these cortical thinning events reflect fine-tuning and synaptic pruning of neurons. Combined with the rapid rise and fall of white matter integrity, it appears that these brain anatomy changes occur as part of a large-scale remodeling of the brain. So, it’s no wonder that pregnant women experience so many emotional and cognitive changes.

The greatest limitation of the study was that it only had a single subject, so we don’t know if other pregnant women show the same brain patterns as Dr. Chrastil. It’s plausible that the brain doesn’t change as much during a second or third pregnancy compared to the first. It’s likely that these brain changes are different in women who are pregnant at a younger age, are pregnant with twins or multiplets, who deliver prematurely, or deliver via C-section.

Co-author Dr. Laura Pritschet called the study a “proof of concept.” The UC Irvine neurobiology research group is already enrolling more women in brain imaging studies, with the goal of being able to compare image sets between healthy and unhealthy pregnancies. This could shed more light on pregnancy-related brain disorders such as postpartum depression, and how to prevent or treat them. Understanding how female sex hormones affect the brain could also bolster the research and treatment of menstrual- and menopause-related illnesses.

This study generates more questions than answers, but it is an important first step toward understanding how pregnancy and childbirth affect the human brain.