Sure, it’s sweet to be pregnant. But did you know that as your hormones surge during pregnancy, your metabolism 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 (the most important of which is sugar) to your baby.

The sweet life

In a non-pregnant person, when you eat food, your body converts it to energy in the form of a sugar called glucose. That glucose goes through your liver, where it’s processed into fat, proteins, and carbohydrates. It’s then shuttled around your body to help your muscles and tissues function.

Glucose needs assistance, specifically something to help it move from your bloodstream into your cells to provide the energy you need to breathe, make your heart beat, and even to do the missionary mambo that got you into this condition in the first place.

Your pancreas helps by providing the hormone insulin, which chaperones glucose throughout your body and facilitates its entry into your cells. In a perfect world, there’s just the right amount of glucose, and just the right amount of insulin, and life is simply swell.

Baby needs some sugar, too

Now, consider what happens when the metabolic storm comes rolling in, in the form of—bada-bing—little fetus Leonard. Lenny’s not quite ready for smashed turnips when he’s turning laps in the amniotic fluid. In fact, what he needs is some of mom’s chemical nectar to keep him growing in utero. Yep, that energy-giving nectar is—you got it—glucose.

Because your baby’s brain depends on glucose, your placenta’s on a mission to make sure that the glucose cupboard is never bare. In fact, if your baby’s blood sugar drops below the magic number—90 milligrams per deciliter of blood (mg/dl)—for even a few minutes, little Lenny could 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 normal concentration. When it blocks insulin’s ability to transport glucose into your cells, it allows your baby to get the glucose he needs to grow. And you can see why: No glucose for baby, no development; no development, no birth.

Human placental lactogen acts like maternal growth hormone, helping you grow appropriately as well. This hormonal dance ultimately influences whether your baby will achieve a healthy weight in utero. 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 his future health after birth.

When babies are big

In some circles, a sort of badge of honor comes with carrying and delivering a big baby. But there are many reasons why you don’t want your baby to be too big. First, 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. When hPL boosts maternal blood glucose, this leaves more glucose circulating in mom’s bloodstream, ready to satisfy the glucose-greedy fetus. That’s a good thing. Bubba needs glucose to grow. But it comes with a price.

To counteract your rising sugar levels as your pregnancy progresses, you secrete more insulin. Your placenta then responds by pumping out even more hPL, which limits the effectiveness of that extra insulin. If your muscles and liver can’t 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 cycle escalates into full-blown gestational diabetes (which is, among other things, a risk factor for prenatal and postpartum depression).

One problem with gestational diabetes is that mom’s excess sugar freely passes through the placenta to the fetus. Now, Bubba has excess sugar in his blood, and his pancreas must increase production of its own insulin too. This insulin increase acts like a growth hormone, and your baby gains weight too quickly, ending up on the heavy side.

While it may seem like no big deal for your baby to pack a few extra pounds at birth (“A future offensive lineman!,” shouts the uncle), a chunky fetus makes more fat cells in utero. So now your baby is not only prone to being overweight as a child, he’s also prone to storing fat as he gets older.

There are other risks with gestational diabetes as well: Your doctor may want to deliver your baby a bit earlier than your due date if she thinks he’s getting too big for your britches. And because lung development may not be complete if the baby is delivered early, premature delivery places him at risk for breathing problems and other health issues after birth.

When baby doesn’t grow well

Gestational diabetes can also pose problems for you. With insulin resistance, the extra sugar in your bloodstream acts like shards of glass, scraping up the walls of your arteries and potentially inflaming the blood vessels that go to the placenta. When this happens, you can actually end up depriving your baby of oxygen and vital nutrients.
If you go into pregnancy with diabetes, it can lead to the opposite extreme of the bell curve with a condition known as intrauterine growth restriction (IUGR)—or when baby isn’t gaining enough weight. This can hamper brain development and create an immune deficiency. Evidence shows that this also contributes to a wide range of problems when these babies become adults, including hormonal, metabolic (obesity) and even heart problems.

There are many causes of this condition, which affects the smallest 5% of babies. For example, it can occur when you’re not eating enough or you’re suffering from so much nausea that you’re losing weight and can’t keep nutrients down.

Gestational diabetes and you

Considering that as many as 10% of pregnant women get gestational diabetes, you’re probably wondering who’s at risk. Because of the surge of hPL, all pregnant women are put into this hypermetabolic state of insulin resistance, and most women’s bodies are able to adjust just fine.

The problem happens when women have additional risk factors, stemming from either a family history of diabetes or gaining too much weight during pregnancy. Nearly 30% of women who gain 40 or more pounds during pregnancy have heavy babies. If you’re already overweight, have had a large baby in the past, have a strong family history of diabetes, or are older than 25, you might be more susceptible to responding poorly to hPL and at greater risk for developing gestational diabetes.

If you want to prevent gestational diabetes, exercise daily (no excuses) and avoid gaining too much weight. If you are diagnosed with it, your care provider will put you on a special diet, encourage you to exercise, and teach you how to monitor your blood sugar level, which you’ll have to test several times a day to help prevent the negative consequences to you and your baby.