Gestational Diabetes: Screening, Management and After the Birth

Gestational diabetes mellitus (GDM) is diabetes first detected in pregnancy. It is common, usually manageable, and worth taking seriously: uncontrolled hyperglycaemia increases the risk of a large-for-gestational-age baby, birth complications, neonatal hypoglycaemia and pre-eclampsia, and it identifies a woman at substantially higher lifetime risk of type 2 diabetes. This guide follows the Queensland Clinical Guidelines (2021), widely used as a reference standard for maternity services.

Screening and diagnosis

All pregnant women are offered screening, usually between 24 and 28 weeks, with earlier testing for those at higher risk — previous GDM, a BMI over 30, a family history of diabetes, a previous large baby, polycystic ovary syndrome, or belonging to a higher-risk ethnic group. The standard test is a 75 g oral glucose tolerance test after an overnight fast, with blood glucose measured fasting and at one and two hours. Diagnosis is made when any threshold is met: fasting 5.1 mmol/L or above, one hour 10.0 mmol/L or above, or two hours 8.5 mmol/L or above. Earlier in pregnancy, a clearly elevated fasting or random glucose, or an HbA1c above the local diagnostic threshold, may indicate pre-existing rather than gestational diabetes — a different and more intensive pathway.

First-line management

Most women are managed initially with lifestyle change: individualised dietary advice from a dietitian, moderate regular physical activity appropriate to pregnancy, and structured self-monitoring of blood glucose — typically fasting and one or two hours after meals, aiming for targets such as fasting under 5.3 mmol/L and one-hour post-meal under 7.8 mmol/L (two-hour under 6.7 mmol/L), using locally agreed thresholds. Weight management is individualised; weight loss is not pursued during pregnancy. A period of two weeks of structured lifestyle management, with review, is a common sequence before medication is added.

When medication is needed

If glucose targets are not met, medication is added — this is a sign that the placenta is driving insulin resistance, not a personal failure. Metformin is often used first where acceptable and not contraindicated; insulin is the traditional mainstay and is preferred when metformin is unsuitable, when targets are far from goal, or when additional control is required. Glibenclamide is used in some services. Treatment is adjusted across pregnancy as insulin resistance rises, especially in the third trimester.

Monitoring the pregnancy

GDM usually does not require early delivery by itself. Care includes regular fetal growth ultrasound — because fetal overgrowth changes the delivery plan — blood pressure and urine screening for pre-eclampsia, and discussion of induction or caesarean timing when the baby is estimated large or other complications arise. Neonatal care anticipates low blood sugar in the first hours after birth; skin-to-skin contact and early feeding are protective, and the baby is checked according to local protocol.

After the birth

Most women's glucose returns to normal quickly, and diabetes medication is usually stopped immediately after delivery. But the diagnosis is a long-term signal: a glucose tolerance test at around six to twelve weeks postpartum confirms recovery, and lifelong screening for type 2 diabetes every one to three years is recommended. Breastfeeding, gradual weight reduction, and an active lifestyle measurably reduce that future risk — and GDM recurs in a substantial proportion of subsequent pregnancies, so early screening next time matters.