Through that discussion, you’ll learn about why some children grow too much, why some don’t grow enough, and if that is the case for you, how you can guide your baby back to the middle.
Metabolic Magic: How Your Nutrition Influences His
Factoid: How often does your baby move? Unless you’ve got a counter, it’s hard to keep up. At twenty weeks, the average is about 200 times a day. At thirty-two weeks, it’s 575. At forty weeks, that number drops to about 300. The reason? There’s less room for the tyke to move around as it grows.
Remember from our introduction about how pregnancy is a lot like a ballroom dance, with you and your partner nudging each other in different directions? Nowhere does this dance play out more than when it comes to metabolism. As your hormones surge during pregnancy, your body changes too. It changes the way it processes energy, it changes the way you store fat, and ultimately it changes the way you deliver nutrients to your baby.
Considering the torture you’ve already put your body through at various times in your life,* you’re already pretty aware of how amazingly responsive human metabolic processes can be. For example, our bodies are able to weather all kinds of biological storms, adapting to such things as high altitudes and extreme climates. Your metabolism also makes adjustments when it sees another kind of biological storm: pregnancy.
In a nonpregnant person, metabolism typically works this way (see figure 4.1). When you eat food, your body converts it to energy in the form of the sugar called glucose. That glucose goes through the liver, where it’s processed into fat, proteins, and carbohydrates, and gets shuttled around your body to help your muscles and tissues function.
Figure 4.1 Energy Efficient When you eat, your body takes the calories and converts them to glucose, your body’s energy source. With insulin serving as glucose’s carrier pigeon, that glucose is shuttled throughout the body to help all of your muscles and organs function smoothly. In pregnancy, that system often is much more resistant, as your body needs to make sure to provide the glucose to your baby.
Glucose, like underage airplane passengers, can’t travel alone. It needs some assistance: specifically, something to help it get from the bloodstream into the cells to provide the energy you need to breathe, to make your heart beat, and even to do the missionary mambo that got you into this condition in the first place.
The pancreas provides the hormone insulin, which chaperones glucose throughout the body and facilitates its entry into the cells. It’s a nice, efficient system that allows the food you eat to provide the energy that all parts of your body need to function. In a perfect world, there’s the right amount of glucose, the right amount of insulin, and life is simply swell.
Now, consider what happens when the metabolic storm comes rolling in, in the form of—bada-bing—little Leonard. Lenny’s not quite ready for smashed turnips when he’s doing laps in amniotic fluid, so he needs some of mom’s chemical nectar to keep him growing in utero. And yep, that energy-giving and baby-growing nectar comes in the form of—you got it—glucose.
Because the baby’s brain depends on glucose, the placenta’s mission is to make sure that the glucose cupboard is never, ever bare. In fact, if the fetus’s blood sugar drops below the magic number—90 milligrams per deciliter of blood (mg/dl)—for even a few minutes, the fetus can suffer irreversible brain damage. So the placenta produces a hormone called human placental lactogen (hPL), which inhibits mom’s insulin from getting glucose into her cells, thereby increasing mom’s bloodstream glucose levels available to baby. Big-time. The hormone hPL is almost identical in structure to the growth hormone present in all women. But in pregnant women, it can reach a thousand times the equivalent normal concentration. And you can see why: no glucose for baby, no development; no development, no birth. Human placental lactogen acts like maternal growth hormone, helping all the mother’s structures grow appropriately as well.
When hPL blocks insulin’s ability to transport glucose into your cells, it allows your baby to get the glucose he needs to grow. This hormonal dance, delicate and subtle as it is, ultimately influences whether your baby will achieve a target weight during pregnancy or not. And when this dance gets a little bit out of sync—oftentimes through absolutely no fault of the mom—that’s when we start to see issues that can influence both the development of your baby as he grows inside you and your baby’s future health after birth.
The Plump Position: When Big Is Bad
In some circles, there seems to be a sort of badge of honor that comes with carrying and delivering a big baby. We celebrate with—and even admire—moms who can carry and deliver kids who enter this world the size of dishwashers. But there are many reasons why you don’t want your baby to be too big at birth. As we said, you’re programming your child to store weight later in life. Plus, you’re opening yourself up to more potential complications at birth as well as the risk of future conditions such as adult-onset diabetes.
One of the reasons we see XXL babies is because of a metabolic problem in mom called gestational diabetes. Many of us assume that the only way to get diabetes is by pummeling your insides with a four-a-day cheesecake habit, but gestational diabetes works a bit differently. (See “What’s Food Got to Do with It?” on page 96.)
To see exactly how it works, let’s take a closer look at glucose metabolism. When hPL causes the changes that increase maternal blood glucose, this leaves more glucose circulating in mom’s bloodstream, available to satisfy the glucose-greedy fetus. That’s a good thing. Bubba needs glucose to grow. But it comes with a price.
To counteract those rising sugar levels as your pregnancy progresses, you secrete more insulin. So the placenta responds by pumping out even more hPL, which limits the effectiveness of that extra insulin. If your muscles and liver cannot easily use up all that sugar, you may end up with too much glucose floating around in your blood. That’s called insulin resistance, and in some moms, the vicious hPL-insulin cycle escalates into full-blown gestational diabetes (a risk factor, by the way, for prenatal and postpartum depression).
One problem with gestational diabetes is that mom’s excess sugar freely passes through the placenta to the fetus. In response to this excess sugar in its blood, the
The Thyroid Puzzle
Many women already know all about thyroid hormone problems; too much or too little can slow down or speed up metabolism and cause a host of symptoms that can make you feel out of sorts in an all-around kind of way. When you add pregnancy to the mix, thyroid issues can get even more complex.
Typically, a mother’s level of thyroid hormone increases between 10 percent and 30 percent during pregnancy, most likely due to the increase in estrogen. Extra estrogen during pregnancy stimulates your cells to make more proteins with binding sites for thyroid hormone. To fill those binding sites, you make more thyroid hormone, but the amount free in your bloodstream, which stimulates your cells, should remain normal, as the increase in production should balance the increase in binding sites. Sometimes, however, the adjustment is imperfect, and you end up with too much (hyperthyroidism) or too little (hypothyroidism) circulating thyroid hormone, which can cause you to experience metabolic chaos. Thyroid conditions are difficult to diagnose because they share some of the same classic symptoms associated with the hormonal changes in pregnancy, such as frenetic or low energy, excess weight loss or gain, and emotional fluctuations. In addition, hyperthyroidism can occur during pregnancy because two of the hormones produced by the placenta—hCG and hPL—mimic thyroid-stimulating hormone (TSH), which does exactly what its name implies—stimulates the thyroid to produce thyroid hormone.
It’d be nice if you could just pop thyroid medication to handle these problems, but it’s not so easy. Because tests used to determine levels of thyroid-stimulating hormone in your blood often cannot distinguish among TSH, hCG, and hPL, it’s hard to be sure that the thyroid is causing