Hyperglycaemia in pregnancy refers to elevated blood glucose levels occurring during pregnancy and includes both gestational diabetes mellitus (GDM) and pre-existing diabetes (type 1 or type 2 diabetes diagnosed before or during pregnancy). Gestational diabetes mellitus is defined as any degree of glucose intolerance first recognized during pregnancy that does not meet the diagnostic criteria for overt diabetes.

Pregnancy is associated with progressive insulin resistance due to placental hormones, increasing maternal insulin requirements, particularly during the second and third trimesters. Failure of pancreatic β-cells to adequately compensate results in maternal hyperglycaemia, which increases the risk of adverse maternal, fetal, and neonatal outcomes. Early identification, appropriate glycaemic control, and multidisciplinary management are essential for improving pregnancy outcomes.

Pathophysiology

During normal pregnancy, placental hormones including human placental lactogen, progesterone, cortisol, placental growth hormone, and prolactin progressively increase maternal insulin resistance to ensure an adequate glucose supply for fetal growth. In most women, pancreatic β-cells compensate by increasing insulin secretion. However, when insulin secretion is insufficient to overcome pregnancy-induced insulin resistance, maternal hyperglycaemia develops.

Maternal hyperglycaemia readily crosses the placenta, while maternal insulin does not. The resulting fetal hyperglycaemia stimulates excessive fetal insulin secretion (fetal hyperinsulinaemia), which acts as a potent growth factor leading to macrosomia, increased adiposity, and organ enlargement. Following delivery, persistent fetal hyperinsulinaemia may result in neonatal hypoglycaemia. Chronic maternal hyperglycaemia also increases the risk of congenital anomalies in pre-existing diabetes, pre-eclampsia, polyhydramnios, operative delivery, stillbirth, and long-term metabolic disease in both mother and child.

Classification

Hyperglycaemia in pregnancy is classified into:

Gestational diabetes mellitus

Glucose intolerance first recognized during pregnancy that does not meet the diagnostic criteria for overt diabetes.

Pre-existing diabetes in pregnancy

Women with type 1 or type 2 diabetes diagnosed before pregnancy or first identified during pregnancy using diagnostic criteria for overt diabetes.

Risk factors

Women at increased risk include those with:

• Body mass index (BMI) >25 kg/m²

• Previous gestational diabetes mellitus

• Previous baby weighing more than 4 kg

• Poor obstetric history (including stillbirth, recurrent miscarriage or congenital anomalies)

• Family history of diabetes mellitus

• Impaired fasting glucose or impaired glucose tolerance

• Glycosuria

• Grand multiparity

• Polycystic ovary syndrome

• Maternal age greater than 35 years

Clinical presentation

Most women with gestational diabetes are asymptomatic and are identified through routine antenatal screening.

Possible clinical features include:

• Glycosuria

• Excessive fetal growth

• Polyhydramnios

• Recurrent urinary tract infections

• Recurrent vulvovaginal candidiasis

• Excessive maternal weight gain

• Previous unexplained stillbirth

• Previous macrosomic infant

Maternal complications

Hyperglycaemia during pregnancy increases the risk of:

• Pre-eclampsia

• Pregnancy-induced hypertension

• Polyhydramnios

• Operative or assisted delivery

• Caesarean section

• Progression of diabetic retinopathy

• Progression of diabetic nephropathy

• Maternal infections

Fetal and neonatal complications

Potential complications include:

• Macrosomia

• Shoulder dystocia

• Birth trauma

• Neonatal hypoglycaemia

• Respiratory distress syndrome

• Hyperbilirubinaemia

• Stillbirth

• Neonatal intensive care admission

• Increased future risk of obesity and type 2 diabetes mellitus

Diagnostic criteria

Overt diabetes during pregnancy

Women should be managed as having pre-existing diabetes if any of the following are present:

• HbA1c ≥6.5%

• Fasting plasma glucose ≥7.0 mmol/L

• Two-hour plasma glucose ≥11.1 mmol/L

Gestational diabetes mellitus

Diagnosis is established by a 75 g oral glucose tolerance test (OGTT) when one or more of the following values are present:

Investigations

Screening at the first antenatal visit

Women should be screened at their first antenatal visit if they have one or more risk factors:

• BMI >25 kg/m²

• Previous gestational diabetes mellitus

• Previous macrosomic infant

• Poor obstetric history

• Family history of diabetes mellitus

• Impaired fasting glucose or impaired glucose tolerance

• Grand multiparity

• Glycosuria

Women with:

• HbA1c ≥6.5%

• Fasting plasma glucose ≥7.0 mmol/L

• Two-hour plasma glucose ≥11.1 mmol/L

should be treated as having pre-existing diabetes.

Women with:

• HbA1c 6.0–6.4%

• Fasting plasma glucose 5.1–6.9 mmol/L

• Two-hour plasma glucose 8.6–11.0 mmol/L

should undergo close monitoring and, if necessary, a 75 g oral glucose tolerance test at 24–28 weeks of gestation.

Screening later in pregnancy

• Women with risk factors should undergo a 75 g oral glucose tolerance test at 24–28 weeks.

• Low-risk women should undergo fasting plasma glucose testing between 24 and 28 weeks.

Routine monitoring during pregnancy

At each antenatal visit assess:

• Self-monitoring blood glucose (SMBG)

• Blood pressure

• Urine protein

• Urine ketones

Additional monitoring includes:

• Eye examination during each trimester

• Renal assessment using urine albumin-to-creatinine ratio and serum creatinine

• Fetal growth monitoring according to obstetric recommendations

Glycaemic targets

Recommended glycaemic targets during pregnancy are:

Pharmacological therapy should be initiated when:

• Fasting or preprandial glucose ≥5.5 mmol/L

• Two-hour postprandial glucose ≥7 mmol/L at ≤35 weeks of gestation

• Two-hour postprandial glucose ≥8 mmol/L after 35 weeks of gestation

• Any postprandial glucose >9 mmol/L

Management

Management should involve a multidisciplinary team including:

• Obstetrician

• Physician (diabetologist or internist)

• Diabetes educator

• Dietitian where available

• Paediatrician or neonatologist

Non-pharmacological management

Pre-pregnancy care

Women with known diabetes who are planning pregnancy should:

• Achieve optimal glycaemic control before conception

• Receive folic acid 5 mg daily before conception and continue until 12 weeks' gestation

• Undergo retinal examination

• Undergo renal assessment including urine albumin-to-creatinine ratio and serum creatinine

• Receive counselling regarding pregnancy risks

Lifestyle management

Lifestyle modification is the preferred initial treatment for gestational diabetes.

Management includes:

• Individualized nutritional therapy

• Controlled and appropriate gestational weight gain

• Even distribution of carbohydrate intake

• Regular self-monitoring of blood glucose

• Moderate physical activity, particularly walking

• Patient education regarding glucose monitoring and hypoglycaemia

Pharmacological management

Pharmacological treatment should be initiated when lifestyle measures fail to achieve glycaemic targets.

Oral hypoglycaemic agents

Metformin

• 500 mg orally every 12 hours

• Increase gradually to a maximum of 2,000 mg daily in two or three divided doses

OR

Glibenclamide

• 2.5 mg orally once daily

• Increase gradually to a maximum of 10 mg daily

Only metformin and glibenclamide are recommended oral glucose-lowering medicines during pregnancy. Other oral hypoglycaemic agents are contraindicated.

Insulin therapy

Insulin should be considered when glycaemic targets cannot be achieved with lifestyle modification and oral therapy, or when clinically indicated.

Rapid-acting insulin analogues are preferred because they provide improved postprandial glucose control and reduce the risk of nocturnal hypoglycaemia.

Preferred rapid-acting insulin analogues include:

• Insulin lispro

• Insulin aspart

Women already receiving lispro or aspart before conception may continue these preparations during pregnancy.

Patients using regular human insulin may be switched to rapid-acting insulin analogues when postprandial glucose remains above target or recurrent pre-meal or nocturnal hypoglycaemia occurs.

Postnatal follow-up

Women diagnosed with gestational diabetes should:

• Undergo glucose testing 6–12 weeks after delivery to confirm return to normal glucose tolerance.

• Continue diabetes screening every 1–2 years because of the increased risk of developing type 2 diabetes mellitus.

• Be encouraged to breastfeed.

• Continue metformin or glibenclamide if clinically indicated during breastfeeding.

• Undergo retinal review one year postpartum if diabetic retinopathy was present during pregnancy.

Prevention

Preventive measures include:

• Pre-pregnancy counselling for women with diabetes

• Achieving optimal glycaemic control before conception

• Maintaining a healthy body weight

• Early antenatal booking

• Risk-based screening at the first antenatal visit

• Appropriate screening at 24–28 weeks of gestation

• Healthy diet and regular physical activity during pregnancy

• Appropriate gestational weight gain

• Regular antenatal follow-up

• Postpartum screening for diabetes

Outcome

With early diagnosis, appropriate lifestyle modification, timely initiation of pharmacological therapy when indicated, and close multidisciplinary follow-up, most women with hyperglycaemia in pregnancy achieve good maternal and fetal outcomes. Poorly controlled hyperglycaemia is associated with increased risks of maternal complications, adverse pregnancy outcomes, neonatal morbidity, and future development of type 2 diabetes mellitus in both mother and child. Regular postpartum follow-up and continued lifestyle modification are essential to reduce long-term metabolic risk.