Gestational Diabetes

Why gestational diabetes happens

The placenta produces hormones (including human placental lactogen, progesterone and cortisol) that make the mother's cells less responsive to insulin. This is normal: it keeps more glucose in the blood for the growing baby. Most people's pancreas compensates by making two to three times more insulin. When it cannot keep up, blood sugar rises and gestational diabetes develops.

Insulin resistance increases through pregnancy, which is why gestational diabetes usually appears after 20 weeks and why testing is done at 24 to 28 weeks. Diabetes found before 20 weeks often means previously unrecognized type 2 diabetes, which is managed as pre-existing diabetes in pregnancy.

Risk factors

• BMI of 30 or more (or 25 or more, or 23 or more in Asian Americans, for early testing)
• Gestational diabetes in a previous pregnancy
• A previous baby weighing 9 lb (4 kg) or more
• A parent or sibling with diabetes
• Prediabetes or polycystic ovary syndrome
• Age over 35
• Hispanic, Black, Native American, South Asian, East Asian or Pacific Islander background
• High blood pressure, high triglycerides or low HDL cholesterol
• Physical inactivity

Many people with gestational diabetes have none of these, which is why testing is universal.

Symptoms

Most people feel nothing unusual. When blood sugar is quite high, there may be:

• Excessive thirst
• Passing urine more often than usual even for pregnancy
• Tiredness
• Blurred vision
• Recurrent yeast or urinary infections

These overlap with normal pregnancy, so they are not reliable. Testing is the only way to know.

Testing for gestational diabetes

US practice uses one of two approaches between 24 and 28 weeks:

Two-step test (most common in the US)

1. 1-hour glucose challenge test: drink 50 g of glucose, no fasting needed, then a blood test 1 hour later. A result of 130 to 140 mg/dL or above (the cutoff varies by practice) leads to the second step.
2. 3-hour oral glucose tolerance test: after an overnight fast, drink 100 g of glucose, with blood drawn fasting and at 1, 2 and 3 hours. Two or more high values confirm gestational diabetes.

One-step test

A 2-hour 75 g glucose tolerance test after fasting. One value at or above any of these confirms the diagnosis: fasting 92 mg/dL (5.1 mmol/L), 1 hour 180 mg/dL (10.0 mmol/L), 2 hours 153 mg/dL (8.5 mmol/L).

People with risk factors are usually tested at their first prenatal visit as well.

Blood sugar targets

Once diagnosed, you check your blood sugar with a finger-stick meter, typically 4 times a day: on waking and after each meal. Common ACOG and ADA targets are:

Your care team may set slightly different targets.

Treatment

Eating plan

A registered dietitian usually creates a personalized plan. Typical principles:

• Spread carbohydrates across 3 meals and 2 to 3 snacks, including a bedtime snack to help fasting readings.
• Limit carbohydrates at breakfast, when insulin resistance is highest.
• Choose whole grains, beans, vegetables, fruit with skin, and pair carbohydrates with protein or healthy fat.
• Avoid sugary drinks, juice, sweets and large portions of white bread, rice, pasta and potatoes.
• Do not skip meals or try to lose weight during pregnancy.

Physical activity

About 30 minutes of moderate activity on most days, such as brisk walking or swimming, lowers blood sugar. A 10 to 15 minute walk after meals is particularly effective. Check with your provider if you have pregnancy complications.

Medicine

If targets are not met within 1 to 2 weeks:

• Insulin is the preferred medicine in the US. It does not cross the placenta.
• Metformin is an alternative in some cases. It crosses the placenta, and its long-term effects on children are still being studied.

Monitoring the baby

Extra ultrasounds check the baby's growth and the amniotic fluid. If you need medicine, you may have twice-weekly fetal monitoring from around 32 weeks. Delivery is usually recommended at 39 to 40 weeks with diet-controlled diabetes, and sometimes earlier with medicine-treated or poorly controlled diabetes.

Risks if it is not controlled

For the baby

• Large baby (macrosomia): extra glucose crosses the placenta and makes the baby store fat. This raises the risk of shoulder dystocia, birth injury and cesarean birth.
• Low blood sugar after birth, because the baby is used to making extra insulin. Babies are checked and fed early.
• Breathing problems, jaundice and a higher risk of stillbirth when control is poor.
• Higher risk of obesity and type 2 diabetes later in childhood.

For the mother

• Preeclampsia and high blood pressure
• Cesarean delivery
• Gestational diabetes in future pregnancies (about half)
• Type 2 diabetes: up to about half develop it within 5 to 10 years

After the baby is born

Blood sugar usually returns to normal within days of delivery, and diabetes medicines are stopped. Have a 75 g glucose tolerance test 4 to 12 weeks after birth, then a diabetes screen every 1 to 3 years for life. Breastfeeding, returning to a healthy weight and staying active lower the risk of type 2 diabetes.

Prevention

Reaching a healthy weight before pregnancy, staying active during pregnancy and avoiding excess weight gain lower the risk. There is no guaranteed way to prevent it, and getting it is not your fault.

Frequently asked questions

What are the first signs of gestational diabetes?

Most people have no signs, which is why routine testing at 24 to 28 weeks matters. If blood sugar is high, you might notice increased thirst, more frequent urination, tiredness or blurred vision, but these are also common in normal pregnancy.

What should I eat if I have gestational diabetes?

Eat regular meals and snacks with controlled carbohydrate portions, choosing whole grains, beans, vegetables and fruit, paired with protein. Keep breakfast low in carbohydrates and avoid sugary drinks, juice and sweets. A dietitian can tailor portions to your blood sugar readings.

Does gestational diabetes go away after birth?

In most people, yes, within days of delivery. But it can return in later pregnancies, and up to half of people with gestational diabetes develop type 2 diabetes within 5 to 10 years. A glucose test 4 to 12 weeks after birth, then regular checks, are recommended.

Can gestational diabetes harm my baby?

Well-controlled gestational diabetes usually leads to a healthy baby. Poor control raises the risk of a large baby, birth injuries, low blood sugar after birth, breathing problems and, rarely, stillbirth. Keeping your readings in target substantially reduces these risks.

What is a normal glucose level in pregnancy?

Common targets for people with gestational diabetes are a fasting level under 95 mg/dL (5.3 mmol/L), under 140 mg/dL (7.8 mmol/L) one hour after meals, or under 120 mg/dL (6.7 mmol/L) two hours after meals. Your provider may set individual targets.

Can I fail the 1-hour glucose test and not have gestational diabetes?

Yes. The 1-hour test is a screen, and many people who fail it pass the 3-hour diagnostic test. Only a positive 3-hour or 2-hour glucose tolerance test confirms gestational diabetes.