other loved one), job termination, or being a victim of a crime. Income is a big factor too, especially around the poverty line. Other factors may not seem so obvious: a lack of friends (social isolation), sustained dissatisfaction at work, or a long-term illness.
Of course, the story of stress reactivity isn’t simple. Some people appear to weather stressful events better than others. Some are stress resistant; others are stress sensitive. There is increasing evidence that this sensitivity has a genetic component. Women under such a biological dictatorship need to keep stress to a minimum during pregnancy. The key issue, regardless of your background, is a loss of control.
Bull’s-eye: Baby’s stress-response system
Lots of research has gone into trying to understand how maternal stress affects brain development. And we have begun to answer this question at the most intimate level possible: that of cell and molecule. The important stress hormone is cortisol. It’s the star player in a team of nasty molecules called glucocorticoids. These hormones control many of our most familiar stress responses, from making our hearts race like NASCAR autos to a sudden urge to pee and poop. Glucocorticoids are so powerful, the brain has developed a natural “braking” system to turn them off as soon as the stress has passed. A pea-sized piece of neural real estate in the middle of the brain, called the hypothalamus, controls the release and braking of these hormones.
A woman’s stress hormones affect her baby by slipping through the placenta and entering the baby’s brain, like cruise missiles programmed to hit two targets. The first target is the baby’s limbic system, an area profoundly involved in emotional regulation and memory. This region develops more slowly in the presence of excess hormone, one of the reasons we think baby cognition is damaged if mom is severely or chronically stressed.
The second target is that braking system I mentioned, the one that’s supposed to rein in glucocorticoid levels after the stress has passed. Excess hormone from mom can mean baby has a difficult time turning off her own stress hormone system. Her brain becomes marinated in glucocorticoids whose concentrations are no longer easily controllable. The baby can carry this damaged stress-response system into adulthood. The child may have a difficult time putting on the brakes whenever she gets stressed out; elevated levels of glucocorticoids thus become a regular part of her life. If she eventually gets pregnant, she bathes her developing infant with the excess toxic stuff. The fetus develops a partially confused hypothalamus, pumping out more glucocorticoids, and the next-generation brain shrinks further. The vicious cycle continues. Excessive stress is contagious: You can get it from your kids, and you can give it to them, too.
Take back control
Clearly, too much stress is not good for pregnant women or their babies. For optimal development of your baby’s brain, you will want to exist in a less-stressed environment, especially in the last few months of pregnancy. You can’t completely upend your life, of course, which could be stressful on its own. But you can reduce your stress, with your spouse’s tender loving care. We’ll say much more about that in the next chapter. You can also begin identifying the areas in your life where you feel out of control, then deliberately form strategies that will allow you to take back control. In some cases, that means exiting the situation that is causing the stress. A temporary helping of courage will translate to a lifetime of benefit for your baby’s brain.
There are plenty of ways to actively practice general stress relief, too. At www.brainrules.net, we’ve listed a number of techniques known from the research literature to reduce stress. A big one is exercise, which has so many benefits that it is the subject of our fourth and final balancing act.
4. Exercise just the right amount
I am always amazed at the life cycle of wildebeests. They are best known for their spectacular annual migrations in the plains and open woodlands of Tanzania and Kenya, thousands upon thousands of them in hypnotic, constant motion. They move for two reasons. First and foremost, they are looking for new pastures. But wildebeests are also 600-pound steaks on legs; they have to keep moving because they are very popular with predators.
Given this urgency, the most interesting part of their life cycle is their pregnancy and birth. The gestation is nearly as long as a human’s, about 260 days, but the similarities end as soon as labor begins. The mother gives birth quickly. Unless there are complications, she also recovers quickly. So do the calves, typically rising to their feet—well, hooves—an hour after they’re born. They have to. Calves represent the herd’s future, but they are also the herd’s most vulnerable population, liable to become leopard food.
We, too, spent our evolutionary adolescence on these same savannahs, and we share many of the wildebeests’ same predator/prey problems. There are, you might imagine, major differences in birthing and parenting between wildebeests and humans. Women take a long time to recover from birth (it’s that big, overweight brain again, evolution’s secret weapon, forcing itself through a narrow birth canal), and their kids won’t be walking for almost a year. Nonetheless, evolutionary echoes imply that exercise was very much a part of our lives, including during pregnancy. Anthropologists think we walked as many as 12 miles per day.
Fit women have to push less
Does that mean exercise should be a part of human pregnancies? Evidence suggests the answer is yes. There are many reasons to stay fit during pregnancy, but the first benefit is a practical one having to do with labor. Many women report that giving birth is both the most exhilarating experience of their lives and the most painful. Pushing, as you know, is usually the toughest part. Studies show that if you are not in shape, it takes you twice as long to transit through the “pushing phase” of labor than if you are fit. Not surprisingly, fit women perceive this stage as being far less painful.
Because the pushing phase is shorter, babies also are less likely to experience brain damage from oxygen deprivation. If you are afraid of labor, you owe it to yourself to become as fit as possible going into it. And the reasons are argued purely from the Serengeti.
Exercise buffers against stress
Fit mothers also tend to give birth to smarter babies than obese mothers do. There are two reasons for this. One may have to do with the direct effects of exercise—especially aerobic exercise—on a baby’s developing brain. This notion needs more research. More powerful are the data linking aerobic exercise and stress reduction.
Certain types of exercise actually buffer a pregnant woman against the negative influence of stress. Remember those toxic glucocorticoids, the ones that invade neural tissue and cause brain damage? Aerobic exercise elevates a molecule in your brain that can specifically block the toxic effects of those nasty glucocorticoids. This heroic molecule is termed brain-derived neurotrophic factor. More BDNF means less stress, which means fewer glucocorticoids in your womb, which means better baby brain development.
It may sound strange to say, but a fit mom has a much better chance of having a smart baby—or at least one best able to mobilize his or her IQ—than an unfit mom.
Too strenuous, and baby overheats
As usual, though, there’s a balance. A baby can feel and react to the mother’s motion. When her heart rate goes up, so does baby’s. When mom’s breathing rate increases, so does baby’s. But only if the exercise is moderate. During strenuous exercise, especially in the later stages of pregnancy, the baby’s heart rate and breathing begin to decline. The concern is that overdoing it might increase the temperature of the womb or restrict baby’s access to oxygen. As ever, your pediatrician can provide guidance about the amount of exercise you should be doing in these later stages. Your oxygen reserve levels are pretty low by the third trimester, so it’s a good time to wind down strenuous activities in preparation for labor. Swimming is one of the best forms of exercise in later stages; the water helps transfer
