Gestational diabetes develops when your body can’t produce enough insulin to keep up with the extra demands pregnancy places on it. About 8.3% of pregnancies in the United States are affected, up from 6% just five years earlier. The condition isn’t caused by something you ate or did wrong during pregnancy. It’s driven by hormonal changes that are a normal part of carrying a baby.
What Happens in Your Body During Pregnancy
Every pregnancy triggers insulin resistance. This is actually by design: your body becomes less responsive to insulin so that more glucose stays in your bloodstream and reaches the growing fetus. The placenta drives this process by releasing hormones that block insulin’s effects, and these hormones increase substantially after about 20 weeks of gestation.
In most pregnancies, the pancreas responds by ramping up insulin production. The insulin-producing cells physically expand in both number and output, pumping out enough extra insulin to keep blood sugar in a normal range despite the resistance. This adaptive response is what separates a typical pregnancy from one with gestational diabetes.
In some women, those insulin-producing cells can’t keep pace. They fail to expand enough or secrete enough insulin to overcome the rising resistance. Blood sugar starts climbing, and gestational diabetes is the result. The condition typically appears in the second half of pregnancy, when placental hormones are at their highest levels.
Why Some Women Develop It and Others Don’t
The core issue is whether your pancreas has enough reserve capacity to compensate for pregnancy’s insulin resistance. Several factors make that compensation harder. Some are things you can influence, and some aren’t.
- Being overweight before pregnancy. Extra body weight increases baseline insulin resistance, meaning your pancreas is already working harder before pregnancy adds its own demands.
- Previous gestational diabetes. If your pancreas couldn’t keep up in a prior pregnancy, the same limitation is likely to show up again.
- Family history of type 2 diabetes. Genetics play a significant role in how well your insulin-producing cells function under stress.
- PCOS (polycystic ovary syndrome). This hormonal condition is closely linked to insulin resistance even outside of pregnancy.
- Having previously delivered a baby over 9 pounds. A large baby in a prior pregnancy can signal that blood sugar was running higher than normal, even if gestational diabetes wasn’t formally diagnosed.
- Racial and ethnic background. African American, Hispanic, American Indian, Alaska Native, Native Hawaiian, and Pacific Islander women face higher rates, likely due to a combination of genetic and socioeconomic factors.
Age also matters. CDC data shows gestational diabetes rates climb steadily with maternal age, with women over 35 diagnosed at significantly higher rates than those in their 20s. That said, women with none of these risk factors still develop gestational diabetes. Sometimes the pancreas simply can’t meet the challenge for reasons that aren’t fully predictable.
How It’s Diagnosed
Screening typically happens between 24 and 28 weeks of pregnancy, timed to when placental hormones are driving insulin resistance highest. The process usually starts with a one-hour glucose challenge: you drink a sugary solution, and your blood is drawn an hour later. A result below 140 mg/dL is considered normal. A result of 190 mg/dL or higher means gestational diabetes without further testing.
If your result falls between those numbers, you’ll be asked to come back for a longer three-hour test. For this version, you fast overnight, drink the glucose solution, then have your blood drawn at one, two, and three hours. If two or more of those readings come back higher than expected, the diagnosis is gestational diabetes. Women with significant risk factors may be screened earlier in pregnancy.
What High Blood Sugar Does to the Baby
When your blood sugar runs high, that extra glucose crosses the placenta. The baby’s own pancreas responds by producing more insulin, and insulin acts as a growth hormone in the fetus. The result is a condition called macrosomia, where the baby grows larger than normal, particularly in the shoulders and body fat. Babies over 9 pounds are more common in pregnancies with poorly managed gestational diabetes.
A larger baby increases the chance of a difficult delivery, birth injuries, and cesarean section. The baby may also experience low blood sugar shortly after birth, since its pancreas is still producing extra insulin even though the maternal glucose supply has been cut off.
Managing Blood Sugar During Pregnancy
The good news is that gestational diabetes responds well to management, and most women can keep their blood sugar in a safe range. The first steps are dietary changes and physical activity. Eating smaller, more frequent meals that balance carbohydrates with protein and fiber helps prevent blood sugar spikes. Walking or other moderate exercise after meals can also lower glucose levels effectively.
You’ll be asked to monitor your blood sugar several times a day, typically with a finger-stick glucose meter. If diet and exercise aren’t enough to keep numbers in range, insulin or oral medication may be needed. Your care team will adjust the approach as pregnancy progresses, since insulin resistance tends to increase toward the third trimester.
What Happens After Delivery
For most women, blood sugar returns to normal within hours or days of giving birth, once the placenta and its hormones are gone. But gestational diabetes is a strong signal that your body’s insulin system was already near its limits. As many as 50% to 70% of women with gestational diabetes will eventually develop type 2 diabetes, and 30% of those women will be diagnosed within five years of delivery.
That risk isn’t a guarantee. Maintaining a healthy weight, staying physically active, and getting regular blood sugar checks after pregnancy can significantly lower the odds. Most guidelines recommend a glucose test 6 to 12 weeks postpartum and periodic screening every one to three years after that. Breastfeeding also appears to improve insulin sensitivity in the months following delivery.
Reducing Your Risk Before Pregnancy
Because insulin resistance is the underlying trigger, anything that improves your body’s insulin sensitivity before conception helps. Reaching a healthy weight before becoming pregnant is the single most impactful step, since it reduces the baseline burden on your pancreas before pregnancy-related hormones add to it. Regular exercise, even moderate walking, improves how your cells respond to insulin. If you have PCOS or a strong family history of diabetes, working with a healthcare provider before conception gives you the chance to address these factors early.