Gestational diabetes is harmful because persistently high blood sugar during pregnancy forces extra glucose across the placenta to the baby, triggering a chain of complications for both of you. The risks range from a larger, harder-to-deliver baby and dangerous blood pressure spikes during pregnancy to a significantly higher chance that both mother and child develop type 2 diabetes later in life. Most of these risks scale with how high and how long blood sugar stays elevated, which is why early detection and management matter so much.
What Happens in Your Body
During any pregnancy, the placenta releases a mix of hormones that make your cells less responsive to insulin. This is actually normal: it keeps more glucose circulating in your blood so the baby has fuel to grow. In most women, the pancreas compensates by producing more insulin. Gestational diabetes develops when that compensation falls short and blood sugar climbs beyond healthy levels.
No single hormone is responsible. Placental growth hormone, cortisol, estrogen, progesterone, and a hormone called human placental lactogen all contribute to insulin resistance. Researchers have tried to pin the effect on one culprit, but studies point in different directions. One found cortisol was the strongest predictor; another pointed to triglycerides and leptin. The practical takeaway: pregnancy naturally pushes your metabolism toward higher blood sugar, and some women’s bodies can’t keep up.
How It Affects the Baby During Pregnancy
The core problem is simple. Glucose crosses the placenta freely, but insulin does not. When your blood sugar runs high, your baby is bathed in excess glucose. The baby’s own pancreas responds by overproducing insulin, and that combination of high sugar plus high insulin acts like a growth accelerant. The baby puts on extra fat and tissue, particularly around the shoulders and trunk, a condition called macrosomia (birth weight over about 8 pounds 13 ounces, or 4,000 grams).
A larger baby doesn’t just mean a harder delivery. It raises the risk of shoulder dystocia, where the baby’s shoulders get stuck behind the pelvic bone after the head delivers. In a study of over 167,000 deliveries, women with diabetes had roughly double the risk of shoulder dystocia even when their babies weighed under 4,000 grams. That’s a critical finding: the risk isn’t limited to the biggest babies. Something about diabetic growth patterns, likely the disproportionate fat distribution around the shoulders, makes delivery more dangerous at every size.
What Happens to the Baby After Birth
Once the umbilical cord is cut, the constant supply of your glucose stops. But the baby’s pancreas is still in overdrive, pumping out high levels of insulin. With no incoming sugar to match, blood sugar drops, sometimes dangerously. This neonatal hypoglycemia is one of the most common immediate complications, and it’s why babies born to mothers with gestational diabetes are monitored closely in the hours after delivery.
Breathing problems are another concern. Respiratory distress occurs in about 4% of newborns whose mothers had gestational diabetes, and the rate is even higher (around 15%) when the mother had diabetes before pregnancy. Babies who struggle with blood sugar or breathing are more likely to need time in the NICU, which can mean separation from the mother during a critical bonding window.
Higher Risk of Stillbirth
This is the risk that worries most parents, and the data confirms it’s real. Women with gestational diabetes have an overall 34% higher relative risk of stillbirth between 36 and 42 weeks compared to women without diabetes. The elevated risk is most pronounced at 37 weeks, where the relative risk is 84% higher, and remains significant through 39 weeks. This is one reason many providers recommend closer monitoring or earlier delivery for women with gestational diabetes, often around 39 weeks.
Risks to the Mother During Pregnancy
Gestational diabetes doesn’t just affect the baby. It significantly raises your risk of preeclampsia, a dangerous condition involving high blood pressure and organ stress. One cohort study found that when gestational diabetes is detected before 20 weeks, the risk of preeclampsia is up to eight times higher. Even when diagnosed later, the association remains strong.
Cesarean delivery rates are also substantially higher. In one analysis, 57% of women with gestational diabetes delivered by C-section. Another study comparing women with and without gestational diabetes found rates of 69% versus 35%. The reasons compound: a larger baby, a higher chance of shoulder dystocia, and a greater likelihood of labor complications all push toward surgical delivery, which carries its own recovery time and risks for future pregnancies.
Long-Term Risks for the Mother
Gestational diabetes is often framed as a temporary condition that resolves after delivery, and for most women, blood sugar does return to normal within weeks. But the metabolic vulnerability it revealed doesn’t disappear. According to the CDC, about half of women who have gestational diabetes go on to develop type 2 diabetes. The insulin resistance that surfaced during pregnancy was a warning signal: your body was already struggling to manage glucose under stress, and aging, weight gain, or another pregnancy can tip the balance again.
This is why postpartum glucose screening is recommended, typically 6 to 12 weeks after delivery and then periodically for years afterward. Many women skip these follow-ups, which means the window to catch prediabetes early, when lifestyle changes are most effective, gets missed.
Long-Term Risks for the Child
The effects on the baby extend well beyond the delivery room. Children born large for gestational age to mothers with diabetes show higher rates of childhood overweight, with measurable differences in body mass appearing as early as six months of age. Macrosomia at birth is one of the strongest independent predictors of childhood overweight, carrying roughly 4.4 times the odds compared to normal-weight newborns.
By ages six to eight, children who are overweight already show significantly higher insulin resistance than their normal-weight peers. This sets the stage for the same metabolic problems their mothers faced: prediabetes, type 2 diabetes, and cardiovascular risk factors that can track into adulthood. The effect appears to be driven both by the intrauterine environment (the months of excess glucose exposure that programmed the baby’s metabolism) and by shared family factors like diet and activity patterns after birth.
Why Blood Sugar Targets Are Tight
Given everything above, it makes sense that the blood sugar goals for gestational diabetes are stricter than for general diabetes management. The American College of Obstetricians and Gynecologists recommends keeping fasting blood sugar below 95 mg/dL, one-hour post-meal readings below 140 mg/dL, and two-hour post-meal readings below 120 mg/dL. These targets are designed specifically to reduce macrosomia risk.
Most women start with dietary changes and physical activity. Carbohydrate quality and timing, rather than extreme restriction, are the focus. When blood sugar can’t be kept within range through food and movement alone, medication is added. The good news is that well-managed gestational diabetes dramatically reduces every risk listed above. The condition is “bad” largely in proportion to how poorly it’s controlled, which is exactly why screening, monitoring, and treatment exist. Women who maintain tight blood sugar control throughout pregnancy have outcomes much closer to those of women without diabetes.