The Neuroscience of... Birth
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Our new series, The Neuroscience of… explores how the brain orchestrates the critical events and behaviors of human life. In this article, we take a look at the numerous changes affecting a mother’s brain before and after birth, and then consider why so little research has been conducted on the brain during birth.
During pregnancy, the human body undergoes far more changes than just a growing baby bump. From a uterus that expands to 500 times its pre-pregnancy size, to a staggering 50% increase in the volume of plasma in the mom-to-be’s bloodstream, these changes affect virtually every system in the body. The brain and nervous system are not excluded from this transformation. While much attention has focused on hormonal changes to the brain, there are significant structural shifts in a mother’s brain before and after birth.
Let’s have a closer look:
- The hormone-secreting pituitary gland increases in size during pregnancy, and while levels of hormones important to maintaining periods, such as follicle-stimulating hormone, become undetectable during pregnancy, others, like prolactin, estrogen and progesterone, increase. One particularly well-known pituitary hormone also spikes during pregnancy…
- Oxytocin – levels of this “love hormone”, also secreted during the formation of romantic relationships, increase rapidly over the course of pregnancy. Oxytocin is thought to cement feelings of attachment between mother and baby after birth. A recent review concluded that higher levels of oxytocin were associated with more affectionate contact behaviors after birth.
- There are also changes to the structure of the brain. A recent long-term brain scanning study, which looked at the volume of different types of structures in the brain during and after pregnancy, noted that gray matter, which contains brain cells called neurons, increased across several brain areas after giving birth. Authors were unclear on whether this rapid change, that is noticeable just a month after birth, was chiefly due to restoration of tissue lost during pregnancy – something noted in previous studies – or to accommodate brain changes related to maternal behavior.
But this extensive research papers over a hole in our understanding of the birthing brain: birth itself, that short period that caps nine months of emotional effort, cravings and worries. What do we know about how mom’s brain changes during birth, and how does that knowledge alter what we know about the rest of pregnancy?
A recent review by Tel Aviv University researcher Dr. Orli Dahan looked at literature surrounding the brain during birth, pointing out the “lacuna” in our knowledge of the brain during birth. While Dahan acknowledges that there may be some challenges to engaging robust academic analysis during what can be, to put it lightly, a stressful time, she also pointed out that there is a substantial volume of literature on what happens to the brain during other not-so lab-friendly experiences, like sex.
Dahan suggests that this “gap” in research might be due to the widespread assumption that brain changes prior to birth are purely for the purpose of preparing the body for motherhood, rather than the big event that precedes it. Likewise, changes post-partum are said to be responses to pregnancy, rather than birth.
So, what do we know about the brain during birth? Some of the most informative studies come from the last 30 years of the 20th century, when, as a recent review by researchers at Salzburg’s Paracelsus Medical University phrases it, “technical, practical and ethical reasons” that would halt such studies today were of less concern. The studies in this analysis showed that oxytocin levels, after months of rising during pregnancy, reach their highest point at birth. The hormone, which is released in “pulses”, were found to spike repeatedly throughout labor, although not in a fashion related to contractions, and then peak at the moment of birth. In addition to helping with mother-child bonding, this oxytocin spike has a number of useful functions during labor, including a positive feedback loop that speeds the passage of the newborn through the birth canal (called the Ferguson reflex) and a strong hypnotic, pain-killing effect.
There are other startling hormonal changes that occur during the act of birth – levels of the hormone norepinephrine, which wakes the body up, are at their highest during this point.
Dahan’s article proposes the theory that a mother’s brain enters a state of “birthing consciousness” during labor. In this state, hormonal changes in the brain, potentially assisted by structural alterations during pregnancy, induce emotional changes like:
- Increases in focus
- Time distortion
- Disinhibition from social constraints
- Pain reduction
- Feelings of calm and peacefulness
These changes, Dahan argues, are permitted by a reduction in blood flow and activity in the prefrontal cortex. This altered state, Dahan says in her paper, is likely to support the mother through childbirth and result in better outcomes – not just improved survival, but with more positive emotional aspects. This theory is supported, says Dahan, by studies of brain plasticity during and after birth. These changes may even last beyond birth – studies of rodents show that female rats who have given birth show increased resilience to stress than those who had not experienced pregnancy – an effect that persisted into old age.
Dahan’s review also looked at factors that might affect the birthing brain. Some aspects of labor that might alter the “birthing consciousness” could make for a smoother delivery. For example, a 2019 study suggested that rates of medical interventions, such as cesarean birth and use of synthetic oxytocin, decrease in delivery rooms with softer lighting.
Interestingly, there is also evidence that the brain itself prepares to protect itself against potential stressors during birth: both findings in humans and rodents show that, late in pregnancy, moms-to-be show reduced responsiveness to negative emotion and psychological stress.
But ultimately, Dahan’s article serves as a call to action for science – she points out in her conclusion that no direct research has been conducted on the neuropsychological state of women during natural or medicated birth. These studies could help to establish whether particular biomarkers or brain states were particularly associated with successful birth – meaning births with no complications, rather than just those where mom and baby both survive. By helping women who give birth and their families, Dahan says, such studies would help just about every human being on earth.