Gestational Diabetes Mellitus (GDM) and Hyperglycaemia in Pregnancy

Overview

Gestational Diabetes Mellitus (GDM) is a form of diabetes that develops during pregnancy in women who did not have diabetes before conception. It is characterized by high blood glucose levels (hyperglycaemia) that are first recognized during pregnancy. Hyperglycaemia in Pregnancy (HIP) is a broader term that includes GDM, diabetes in pregnancy (DIP, where pre-existing diabetes is present), and overt diabetes first diagnosed in pregnancy. Globally, HIP affects about 15.6% of live births, with higher rates in low- and middle-income countries. In Sri Lanka, GDM prevalence varies depending on diagnostic criteria, ranging from 5.5-13.9% to as high as 31.2% using more sensitive thresholds. GDM increases risks for both mother and baby, including preeclampsia, cesarean delivery, macrosomia, and neonatal hypoglycemia. Long-term, it raises the mother's risk of type 2 diabetes (up to 8-fold) and cardiovascular disease. Management focuses on blood glucose control through diet, exercise, and sometimes insulin, with guidelines from organizations like the Sri Lanka College of Obstetricians & Gynaecologists (SLCOG), WHO, and International Diabetes Federation (IDF).

Classification

HIP is classified based on when hyperglycaemia is detected and its type:

• Gestational Diabetes Mellitus (GDM): Hyperglycaemia first detected during pregnancy, typically after 24 weeks, not meeting criteria for overt diabetes.

• Diabetes in Pregnancy (DIP): Pre-existing type 1 or type 2 diabetes diagnosed before pregnancy.

• Overt Diabetes: New-onset diabetes diagnosed in pregnancy with criteria for non-pregnant adults (e.g., fasting glucose ≥7.0 mmol/L or HbA1c ≥6.5%).

In Sri Lanka, the majority of HIP cases are GDM.

Signs and Symptoms

Many women with GDM are asymptomatic, but symptoms can include excessive thirst (polydipsia), frequent urination (polyuria), fatigue, blurred vision, and recurrent infections (e.g., thrush). In advanced cases, it may present with complications like preeclampsia symptoms (high blood pressure, swelling). Fetal signs include excessive growth detected on ultrasound.

Causes and Pathophysiology

GDM results from insulin resistance induced by placental hormones (e.g., human placental lactogen, cortisol) combined with inadequate pancreatic beta-cell compensation. This leads to hyperglycaemia. Genetic factors, obesity, and inflammation play roles. In South Asian populations like Sri Lanka, higher visceral fat and genetic predisposition contribute to earlier onset.

Risk Factors

Key risk factors include:

• Advanced maternal age (>35 years), obesity (BMI >30 kg/m²), family history of diabetes.

• Previous GDM, macrosomia (>4 kg baby), polycystic ovary syndrome (PCOS).

• Ethnicity: Higher in South Asians, including Sri Lankans.

• Multiple pregnancy, sedentary lifestyle.

In Sri Lanka, rising obesity and non-communicable diseases exacerbate risks.

Diagnosis

Diagnosis typically involves a 75g oral glucose tolerance test (OGTT) at 24-28 weeks, or earlier if high-risk.

• Sri Lankan National Guidelines (SLCOG): Fasting ≥5.6 mmol/L, 1-h ≥10.0 mmol/L, or 2-h ≥7.8 mmol/L.

• IADPSG/WHO (2013): Fasting ≥5.1 mmol/L, 1-h ≥10.0 mmol/L, or 2-h ≥8.5 mmol/L.

• WHO 1999: Fasting ≥7.0 mmol/L or 2-h ≥7.8 mmol/L.

Sri Lanka does not recommend universal screening but risk-based, though some studies advocate universal due to high prevalence. Early screening at first visit for high-risk women.

Treatment

Management is multidisciplinary:

• Lifestyle: Medical nutrition therapy (balanced diet, carbohydrate control), physical activity (30 min moderate exercise most days).

• Monitoring: Self-blood glucose monitoring (target: fasting <5.3 mmol/L, 1-h post-meal <7.8 mmol/L, 2-h <6.7 mmol/L).

• Medication: Insulin if targets not met; oral agents like metformin in some cases, though insulin preferred in Sri Lanka.

• Antenatal Care: Frequent visits, ultrasound for fetal growth.

• Intrapartum: Continuous glucose monitoring, aim for vaginal delivery unless complications.

• Postpartum: OGTT at 6-12 weeks to check for persistent diabetes.

In Sri Lanka, follow SLCOG guidelines for secondary/tertiary care.

Prevention

Pre-pregnancy: Achieve healthy weight, screen for diabetes. During pregnancy: Healthy diet, exercise. High-risk women may benefit from early intervention. In low-calcium areas, supplements may help indirectly.

Prognosis

Most cases resolve postpartum, but 50% develop type 2 diabetes within 10 years. In Sri Lanka, women with GDM have higher risks of future metabolic issues. Good control reduces complications.

Epidemiology

Globally, 23.3 million live births (15.6%) affected by HIP in 2024. In South Asia, rates are high; Sri Lanka shows increasing trends (5.7% GDM, 7.1% total HIP). Regional studies report 13.9% in northern Sri Lanka. Prevalence varies by criteria: 13.1% (WHO 1999), 28% (Sri Lankan), 31.2% (IADPSG).

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