Gestational diabetes affects the baby primarily by sending too much sugar across the placenta, which forces the baby’s body to produce extra insulin and can lead to excessive growth, difficult delivery, and blood sugar problems after birth. Most of these effects are preventable when blood sugar is well managed during pregnancy, but understanding the specific risks helps you know what to watch for and why your care team monitors certain things closely.
How Extra Sugar Reaches the Baby
The placenta transfers glucose from your blood directly to your baby. When your blood sugar runs higher than normal, your baby receives more glucose than they need. The baby’s pancreas responds by ramping up insulin production to process all that extra sugar. Unlike glucose, your insulin does not cross the placenta, so the baby has to manufacture their own.
This extra insulin does more than just manage blood sugar. Insulin acts as a growth hormone in a developing baby, driving the body to convert that excess glucose into fat and tissue. The result is a baby that grows larger than normal, particularly around the shoulders and trunk. The pattern of overgrowth, the timing of high blood sugar episodes, and how long they last all influence how much the baby is affected.
Overgrowth and Macrosomia
The most visible effect of gestational diabetes is a bigger baby. Macrosomia, the clinical term for an unusually large newborn, is generally defined as a birth weight above 4,000 grams (about 8 pounds, 13 ounces) or above the 90th percentile for gestational age. Babies of mothers with gestational diabetes don’t just weigh more overall. They tend to carry extra fat around the chest and abdomen, which creates a specific problem during delivery.
That disproportionate growth increases the risk of shoulder dystocia, where the baby’s shoulders get stuck behind the pelvic bone during a vaginal delivery. A large study of over 167,000 deliveries found that mothers with diabetes had roughly twice the risk of shoulder dystocia even when babies weighed under 4,000 grams, compared to mothers without diabetes. When shoulder dystocia did occur alongside diabetes, the risk of birth injury was about 2.3 times higher. This is one reason care teams closely track estimated fetal weight in the third trimester and may recommend a cesarean delivery if the baby measures very large.
Low Blood Sugar After Birth
One of the most immediate concerns after delivery is neonatal hypoglycemia, or low blood sugar in the newborn. While in the womb, the baby has been producing high levels of insulin to handle the constant supply of extra glucose. The moment the umbilical cord is cut, that glucose supply stops, but the baby’s insulin production doesn’t shut off right away. The result is a blood sugar crash.
This typically happens within the first one to two hours after birth. Hospital staff will check your baby’s blood sugar shortly after delivery and continue monitoring it until levels stabilize, which can take a couple of days. Mild cases are managed with early and frequent feeding. If blood sugar doesn’t come up with feeding, the baby may need an IV glucose solution. All babies born to mothers with gestational diabetes are tested for low blood sugar regardless of whether they show symptoms, because hypoglycemia in newborns can be silent.
Breathing Difficulties
Babies exposed to high insulin levels in the womb can have delayed lung maturation. The lungs produce a slippery coating called surfactant that keeps the air sacs from collapsing with each breath. High insulin levels directly interfere with the production of key proteins in that coating, reducing surfactant protein A by as much as 67% and surfactant protein B by about 32% in lab studies. Without enough surfactant, newborns can develop respiratory distress syndrome, where they struggle to breathe on their own.
This risk is highest when gestational diabetes is poorly controlled and when babies are born before full term. In one study of babies born to mothers with gestational diabetes who experienced complications, respiratory distress syndrome was tied with low birth weight and macrosomia as the most common reason for intensive care admission, each affecting about 25% of the affected newborns.
Excess Amniotic Fluid
Gestational diabetes can also cause polyhydramnios, an excess of amniotic fluid. When a baby processes more glucose, they produce more urine, which is a major source of amniotic fluid. In one study of 340 pregnancies with gestational diabetes, about 10% developed polyhydramnios. Higher fluid levels were significantly associated with delivering a larger-than-average baby and, overall, the polyhydramnios group had a 66% rate of perinatal complications compared to 47% in the normal fluid group. Too much amniotic fluid can also increase the risk of preterm labor and umbilical cord problems.
NICU Admission
About 7% of babies born to mothers with gestational diabetes in one study required admission to the neonatal intensive care unit. The most common reasons were respiratory distress, low birth weight, macrosomia, and hypoglycemia. Congenital heart abnormalities accounted for a smaller portion of admissions. Most NICU stays for these babies are short and focused on stabilizing blood sugar or supporting breathing until the baby adjusts to life outside the womb.
Long-Term Health Effects for the Child
The effects of gestational diabetes don’t necessarily end at birth. Children exposed to high blood sugar in utero appear to have a higher chance of becoming overweight during childhood, though the size of that risk is debated. Some studies have found that children of mothers with gestational diabetes were roughly twice as likely to be above the 85th percentile for weight by ages five to seven. However, a CDC systematic review noted that when researchers accounted for the mother’s pre-pregnancy weight, many of those associations weakened or disappeared. In other words, it’s difficult to separate the effect of in-utero sugar exposure from the effect of shared genetics and family eating habits.
There is also evidence that these children face a higher risk of developing insulin resistance and type 2 diabetes later in life. One study found that children who had both a high genetic risk for type 2 diabetes and a mother with gestational diabetes had nearly double the rate of impaired glucose tolerance or type 2 diabetes (about 16%) compared to those with low genetic risk and a mother with gestational diabetes (about 8%). The combination of genetic predisposition and fetal sugar exposure appears to compound the risk.
How Blood Sugar Management Protects the Baby
The good news is that most of these complications are tied to how well blood sugar is controlled, not simply to having a gestational diabetes diagnosis. The American Diabetes Association’s 2026 guidelines recommend keeping fasting blood sugar below 95 mg/dL, and either one-hour post-meal readings below 140 mg/dL or two-hour post-meal readings below 120 mg/dL. Staying within these targets significantly reduces the risk of excessive fetal growth, birth complications, and neonatal blood sugar problems.
For many women, dietary changes and physical activity are enough to hit those targets. When they’re not, insulin or other treatments are added. Research suggests that when gestational diabetes is treated and blood sugar is well controlled, the rates of macrosomia, shoulder dystocia, and neonatal hypoglycemia drop substantially. In the Hillier study, babies of mothers who were treated for gestational diabetes showed no significant increase in childhood overweight compared to babies of mothers without diabetes, while untreated mothers saw roughly 1.8 to 1.9 times the odds of childhood obesity in their children.
Screening typically happens between 24 and 28 weeks of pregnancy, which is when insulin resistance from placental hormones peaks. If you’re diagnosed, the monitoring and management that follow are specifically designed to keep your baby’s environment as close to normal as possible during the final, most growth-intensive stretch of pregnancy.