Diabetes significantly affects pregnancy for both mother and baby. Whether you have type 1 or type 2 diabetes before conceiving, or develop gestational diabetes during pregnancy, elevated blood sugar changes how the placenta develops, increases the risk of complications like preeclampsia and large birth weight, and requires close monitoring throughout all three trimesters.
How High Blood Sugar Affects the Placenta
The core problem in any diabetic pregnancy is excess glucose crossing the placenta. Unlike insulin, glucose passes freely from your bloodstream into the baby’s, exposing the developing fetus to higher sugar levels than normal. In response, the baby’s pancreas produces extra insulin, which acts as a growth hormone and drives many of the complications described below.
High blood sugar also damages the placenta itself. Research shows that placentas in diabetic pregnancies tend to be heavier, with fewer blood vessels in the tissue structures that exchange oxygen and nutrients. The vessels that do form are positioned farther from the maternal blood supply, making oxygen transfer less efficient. This creates a state of chronic low oxygen for the fetus. In severe cases, the combination of impaired blood vessel growth and reduced oxygen exchange contributes to stillbirth, with placental tissue immaturity identified as a key mechanism.
Risks for the Mother
Preeclampsia, a dangerous spike in blood pressure during pregnancy, occurs about twice as often in diabetic pregnancies. Studies show a rate of roughly 10% in women with diabetes compared to about 4% in women without it. Preeclampsia can damage your kidneys, liver, and other organs and sometimes requires early delivery to protect your health.
Other maternal complications include a higher likelihood of cesarean delivery, excess amniotic fluid (which can cause preterm contractions), and urinary tract infections. If you already have diabetes-related kidney disease or eye problems before pregnancy, those conditions can worsen during the nine months of increased metabolic demand. Women with pre-existing diabetes also face a greater chance of preterm labor, either spontaneous or medically induced because of complications.
Risks for the Baby
The most visible effect on infants is macrosomia, meaning the baby grows unusually large. In mothers with gestational diabetes, the rate of macrosomia ranges from about 13% to 16%, compared to 3% to 11% in mothers without it. A larger baby increases the chance of shoulder dystocia during vaginal delivery, where the baby’s shoulder gets stuck behind the pelvic bone, and of birth injuries for both mother and child.
After birth, babies of diabetic mothers commonly experience a temporary drop in blood sugar. The baby has been producing extra insulin to handle the glucose coming through the placenta, and once the umbilical cord is cut, that insulin surplus causes blood sugar to plummet. Hospital staff monitor for this and typically manage it with early feeding or, if needed, intravenous glucose. Other short-term neonatal issues include jaundice, higher-than-normal red blood cell counts, and breathing difficulties.
Birth Defects With Pre-Existing Diabetes
Women who enter pregnancy with type 1 or type 2 diabetes face a meaningfully higher risk of structural birth defects, particularly heart defects. In a large study of nearly 595,000 births, pre-existing diabetes was linked to a 2.8-fold increase in major congenital heart disease. That risk climbed sharply with poor blood sugar control: women whose long-term blood sugar marker (HbA1c) exceeded 8% in the first trimester had an 8.5-times greater risk compared to non-diabetic pregnancies. Neural tube defects, which affect the brain and spinal cord, are also more common.
This is why the first trimester matters so much. The baby’s heart and nervous system form in the earliest weeks, often before a woman even confirms the pregnancy. Gestational diabetes, which typically develops in the second or third trimester, does not carry the same elevated risk of structural birth defects because those organs have already formed by then.
Pre-Existing vs. Gestational Diabetes
Pre-existing diabetes (type 1 or type 2) poses the greatest risks because blood sugar may already be elevated when the baby’s organs are forming. The recommended target for HbA1c before conception is 6.5% or lower. Ideally, women with pre-existing diabetes use reliable contraception until reaching that threshold, then plan conception with their care team already in place.
Gestational diabetes develops when your body can’t produce enough extra insulin to meet the demands of pregnancy. It’s typically diagnosed between weeks 24 and 28 through a glucose tolerance test. The most common screening approach in the U.S. involves drinking a sugary solution and having blood drawn at timed intervals. Diagnostic cutoffs for the standard test are: fasting blood sugar at or above 95 mg/dL, one-hour reading at or above 180 mg/dL, two-hour reading at or above 155 mg/dL, and three-hour reading at or above 140 mg/dL. Meeting two or more of those thresholds confirms the diagnosis.
Blood Sugar Targets During Pregnancy
Whether you have pre-existing or gestational diabetes, blood sugar goals during pregnancy are tighter than for non-pregnant adults. The American College of Obstetricians and Gynecologists recommends:
- Fasting: below 95 mg/dL
- One hour after eating: below 140 mg/dL
- Two hours after eating: below 120 mg/dL
You’ll likely check your blood sugar several times a day, typically first thing in the morning and after each meal. Many women find that a consistent routine of testing, eating on schedule, and tracking results helps them stay within range without feeling overwhelmed.
How Diabetes Is Managed in Pregnancy
The first step for gestational diabetes is usually dietary changes and physical activity. Many women can reach their blood sugar targets by adjusting the timing, portion size, and composition of meals, specifically by pairing carbohydrates with protein and fat to slow glucose absorption. Walking after meals, even for 10 to 15 minutes, also has a measurable effect on post-meal blood sugar spikes.
When diet and exercise aren’t enough, insulin is the first-line medication recommended in the U.S. for managing diabetes during pregnancy. The American Diabetes Association’s 2026 standards specifically advise against using oral medications like metformin or glyburide as first-line treatment because both cross the placenta and reach the baby, and there are concerns about long-term effects on offspring. Some providers still prescribe metformin in certain situations, but the standard recommendation is insulin.
For women with pre-existing type 1 diabetes, insulin management becomes more complex during pregnancy because insulin needs shift dramatically. Insulin requirements often drop in the first trimester, then rise steadily through the second and third trimesters, sometimes doubling or tripling from pre-pregnancy doses. Frequent adjustments with your care team are the norm, not the exception.
What Happens After Delivery
For women with gestational diabetes, blood sugar typically returns to normal within hours or days of delivery. But the pregnancy served as a stress test for your metabolism, and the results carry a warning. A meta-analysis of nearly 62,000 women found that those diagnosed with gestational diabetes were more than six times as likely to develop type 2 diabetes later in life. The cumulative incidence was about 8% within the first five years after delivery and rose to roughly 19% beyond five years. Women with gestational diabetes also had a 3.7-fold higher risk of developing prediabetes compared to women who had normal blood sugar during pregnancy.
Because of this, postpartum glucose screening is recommended, typically at 4 to 12 weeks after delivery and then every one to three years going forward. Maintaining a healthy weight, staying physically active, and continuing the dietary habits that worked during pregnancy are the most effective ways to delay or prevent progression to type 2 diabetes.
Planning Ahead Makes a Difference
The single most impactful factor for women with pre-existing diabetes is blood sugar control before and during early pregnancy. Reaching an HbA1c of 6.5% or lower before conceiving dramatically reduces the risk of birth defects, miscarriage, and other first-trimester complications. For women who develop gestational diabetes, early diagnosis and consistent blood sugar management can bring complication rates close to those of non-diabetic pregnancies. The condition is serious, but with the right monitoring and support, most women with diabetes have healthy pregnancies and healthy babies.