Gestational Diabetes: Symptoms, Testing, Diet, Treatment and After Delivery

Gestational diabetes mellitus (GDM) is high blood sugar that is first recognised during pregnancy. Pregnancy hormones from the placenta make the body more resistant to insulin, usually from the second trimester. Most women make extra insulin to cope, but some cannot, so sugar rises. GDM is common, particularly in South Asian women, and it usually causes no symptoms, which is why testing is so important. With good care, most women with GDM have healthy pregnancies and healthy babies.

Who is at higher risk?

• Age over 30, and especially over 35
• Overweight or a BMI of 23 or more before pregnancy
• Previous gestational diabetes or a very large baby (over 4 kg)
• Family history of diabetes
• PCOS
• Prediabetes
• South Asian ethnicity
• Stillbirth or unexplained pregnancy loss in the past

Symptoms

Most women have none. Some notice thirst, frequent urination, tiredness or recurrent thrush, but these are common in normal pregnancy, so they cannot be relied on.

Testing

Women at high risk are often tested at the first antenatal visit. Everyone should be tested at 24-28 weeks, usually with a 75 g oral glucose tolerance test (OGTT). A diagnosis of GDM is made if any value is at or above:

• 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)

Local hospitals may use slightly different protocols, so follow your doctor's instructions. A glucose of 126 mg/dL (7.0 mmol/L) or more fasting, or HbA1c of 6.5% or more, early in pregnancy suggests diabetes that existed before pregnancy. See our guide to normal blood sugar levels.

Possible effects on mother and baby

When sugar is not controlled, there are risks of:

• A larger baby (macrosomia), leading to difficult delivery, shoulder dystocia or caesarean section
• High blood pressure or pre-eclampsia
• Premature birth
• Low blood sugar, jaundice and breathing problems in the newborn
• Higher risk of stillbirth in poorly controlled cases
• Childhood obesity and diabetes later in the baby's life

Good control brings the risks close to those of women without GDM.

Blood sugar targets

Commonly recommended targets are fasting below 95 mg/dL (5.3 mmol/L), 1 hour after meals below 140 mg/dL (7.8 mmol/L) or 2 hours below 120 mg/dL (6.7 mmol/L). You will usually be taught to check with a glucometer four times a day (fasting and after meals) and keep a diary.

Diet for gestational diabetes

A dietitian can tailor a plan, but key principles are:

• Three small meals and two to three snacks to avoid big sugar peaks and long gaps.
• Spread carbohydrates evenly. Choose red rice, kurakkan, whole-grain bread and pulses in measured portions, and avoid large rice servings.
• Avoid sugary drinks and sweets, including fruit juice and sweetened tea. Eat fruit in small portions.
• Add protein and vegetables to every meal, such as fish, egg, dhal and mallum.
• Do not diet to lose weight. You still need adequate calories and nutrients for the baby. Never skip meals or fast.
• Take folic acid, iron and calcium as advised.

Many women find breakfast the hardest meal because of morning hormone surges, so choose lower-carbohydrate options such as egg and vegetables or dhal with a small portion of starch.

Exercise

Unless your doctor advises otherwise, aim for 30 minutes of walking most days, or swimming and gentle antenatal exercise. A 10-15 minute walk after meals reduces post-meal sugar. Stop and seek help for pain, bleeding, dizziness or breathlessness.

Medicines

About 60-70% of women control GDM with diet and activity alone. If sugar remains above target after one to two weeks, doctors add:

• Insulin: the standard treatment, safe for the baby because it does not cross the placenta.
• Metformin or glibenclamide in some settings, depending on local guidelines.

Medicines are not a failure. They are needed because of hormones, not because you did something wrong. Do not stop or adjust them without advice, and learn the signs of low sugar (shaking, sweating, hunger, confusion).

Care during pregnancy and labour

Expect more frequent antenatal visits and additional scans to check growth and amniotic fluid. Delivery timing depends on control and the baby's size; many women with well-controlled GDM deliver at term (around 38-40 weeks), while those on insulin may be induced earlier. During labour, sugar is monitored. After birth, the baby's blood sugar is checked in the first hours, and early, frequent feeding is encouraged.

After delivery

• Medicines for GDM are usually stopped immediately after birth.
• Have a glucose test 6-12 weeks after delivery (an OGTT or fasting test) to confirm that sugar is normal.
• Repeat testing every one to three years for life, because of the higher risk of type 2 diabetes.
• Breastfeed if possible, return to a healthy weight, keep active and eat well.
• Plan future pregnancies, and get tested before conceiving.

Read how to reverse prediabetes for steps that lower your later diabetes risk.

When to see a doctor urgently

Seek urgent care for reduced baby movements, severe headache, blurred vision, swelling of the face or hands, bleeding, leaking fluid, abdominal pain, vomiting with high sugars, or blood sugar readings repeatedly far above your targets.

References

• International Association of Diabetes and Pregnancy Study Groups: diagnostic criteria for hyperglycaemia in pregnancy
• World Health Organization: diagnostic criteria and classification of hyperglycaemia first detected in pregnancy
• American Diabetes Association: Standards of Care in Diabetes, management of diabetes in pregnancy
• NICE guideline NG3: diabetes in pregnancy