Clinical Subject Page

Gestational Diabetes Mellitus (GDM)

Gestational Diabetes Mellitus (GDM) is diabetes first diagnosed during pregnancy that is not clearly overt pre-existing diabetes. It develops when pregnancy-related insulin resistance exceeds the mother’s ability to increase insulin secretion.

Also called

Pregnancy-related diabetes

ICD-10

O24.4

Specialty

Endocrine

Onset

Chronic

Reviewed

August 2026

Overview

Overview
Etiology & Risk Factors

Etiology & Risk Factors
Pathophysiology

Pathophysiology
Clinical Presentation

Clinical Presentation
History Taking

History Taking
Physical Examination

Physical Examination
Investigations

Investigations
Diagnosis

Diagnosis
Management

Management
Complications

Complications
Prognosis

Prognosis
Key Points / Clinical Pearls

Key Points / Clinical Pearls

Overview

Gestational Diabetes Mellitus (GDM) usually develops in the second or third trimester, when placental hormones increase maternal insulin resistance.
Most women have no symptoms and are diagnosed through routine screening. Gestational Diabetes Mellitus (GDM) increases the risk of macrosomia, shoulder dystocia, preeclampsia, cesarean delivery, neonatal hypoglycemia, and future maternal Type 2 Diabetes Mellitus.

Teaching point Gestational Diabetes Mellitus (GDM) is usually asymptomatic, so appropriate pregnancy screening is essential even when the mother has no symptoms of hyperglycemia.

Etiology & Risk Factors

–Etiology:

Pregnancy causes progressive insulin resistance due to placental hormones, including:

Human placental lactogen
Placental growth hormone
Progesterone
Cortisol
Estrogen

Normally, pancreatic beta cells compensate by increasing insulin secretion.

GDM develops when insulin secretion cannot adequately compensate for pregnancy-induced insulin resistance.

–Inheritance

GDM itself is not inherited in a simple Mendelian pattern.

Genetic susceptibility contributes to the risk, particularly when there is a family history of Type 2 Diabetes Mellitus.

–Risk Factors

Previous Gestational Diabetes Mellitus (GDM)
Previous infant with macrosomia
Overweight or obesity
Family history of Type 2 Diabetes Mellitus
Previous unexplained stillbirth
Polycystic ovary syndrome
Maternal age associated with increased diabetes risk

Pathophysiology

Pregnancy → increased placental hormones → progressive maternal insulin resistance → increased insulin requirement → inadequate pancreatic beta-cell compensation → maternal hyperglycemia → increased fetal glucose exposure → fetal hyperinsulinemia → excessive fetal growth and neonatal metabolic complications

Clinical Presentation

-Symptoms:

Most women are asymptomatic.
Possible symptoms include:
Increased thirst
Increased urination
Fatigue
Blurred vision
Recurrent infections
These symptoms are nonspecific and may overlap with normal pregnancy.

–Signs:

Usually no specific physical signs.
Possible findings include:
Excessive maternal weight gain
Obesity
Hypertension
Large-for-gestational-age fetus on ultrasound

Important Note Gestational Diabetes Mellitus (GDM) should be distinguished from overt diabetes first recognized during pregnancy, because overt diabetes carries different diagnostic and management implications.

History Taking

-Ask about:

Previous Gestational Diabetes Mellitus (GDM)
Previous macrosomic infant
Previous pregnancy complications
Family history of diabetes
History of polycystic ovary syndrome
Pre-pregnancy weight
Weight gain during pregnancy
Symptoms of hyperglycemia
Previous abnormal glucose testing

Physical Examination

–General Examination:

Weight
Body mass index
Blood pressure
Weight gain during pregnancy
General nutritional status

Assess for:

Obesity
Hypertension
Dehydration when significant hyperglycemia is present

–System-Specific Examination

–Obstetric examination:

Fundal height
Fetal growth assessment
Fetal heart rate
Assessment for polyhydramnios when clinically suspected

–Fetal assessment:

Growth assessment by ultrasound when clinically indicated
Assessment for macrosomia or excessive fetal growth

Investigations

-Biochemistry / Specific Tests

Oral Glucose Tolerance Test

-The 75-g oral glucose tolerance test (OGTT) is widely used for diagnosis.

Using International Association of Diabetes and Pregnancy Study Groups (IADPSG)/World Health Organization (WHO)-based criteria, GDM is diagnosed when one or more of the following plasma glucose values are met or exceeded:

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)

-Plasma Glucose

Glucose measurements may be used for:

Screening according to local protocols
Diagnosis
Monitoring treatment

–HbA1c

HbA1c is not generally the preferred test for diagnosing GDM, particularly because physiological changes in pregnancy affect its interpretation.

It may be useful in selected circumstances to assess possible pre-existing diabetes.

Diagnosis

Gestational Diabetes Mellitus (GDM) vis diagnosed when glucose intolerance meeting pregnancy-specific diagnostic criteria is first identified during pregnancy and overt pre-existing diabetes is not present.

Using the 75-g OGTT approach, one abnormal value is sufficient for diagnosis:

Fasting ≥92 mg/dL
1-hour ≥180 mg/dL
2-hour ≥153 mg/dL

Overt diabetes first recognized during pregnancy should be classified separately using standard diabetes diagnostic criteria.

Home Home Clinical Cases Endocrine System Clinical Cases Gestational Diabetes Mellitus (GDM)

Management

1. First-Line / Emergency Management

Most women can initially be managed with:

Medical nutrition therapy
Appropriate physical activity
Self-monitoring of blood glucose
Education regarding glucose targets and pregnancy nutrition

Urgent management is required for:

Severe hyperglycemia
Diabetic ketoacidosis
Hyperglycemic emergencies
Significant maternal or fetal complications

2. Definitive Treatment

The primary goals are:

Maintain pregnancy glucose within recommended targets
Prevent excessive fetal growth
Reduce maternal and neonatal complications
Monitor fetal wellbeing
Plan appropriate delivery and postpartum follow-up

3. Medical Treatment

-Insulin

Insulin is the preferred medication when lifestyle measures do not achieve adequate glycemic control.

Common approaches include:

Basal insulin
Mealtime insulin
Basal-bolus regimens when required

Insulin does not cross the placenta in clinically significant amounts and can be titrated according to glucose monitoring.

-Metformin

Metformin is used in some guidelines and healthcare systems as an alternative or adjunct to insulin.

Its use should follow local pregnancy-diabetes guidelines and involve appropriate counseling.

-Other glucose-lowering medications

Many other non-insulin agents are not routinely recommended during pregnancy because of limited safety data.

Complications

-Maternal Complications

Preeclampsia
Gestational hypertension
Increased risk of cesarean delivery
Excessive maternal weight gain

-Fetal and Neonatal Complications

Fetal macrosomia
Large-for-gestational-age infant
Shoulder dystocia
Birth trauma
Neonatal hypoglycemia
Neonatal hyperbilirubinemia
Respiratory distress

-Long-Term Complications

Type 2 Diabetes Mellitus
Cardiometabolic disease

Prognosis

The prognosis is generally good with appropriate diagnosis and glycemic control.

GDM usually resolves after delivery, but women with GDM have a substantially increased long-term risk of developing Type 2 Diabetes Mellitus.

Future risk is higher with:

Recurrent GDM
Obesity
Higher pregnancy glucose levels
Need for insulin during pregnancy
Strong family history of diabetes

Key Points / Clinical Pearls

Gestational Diabetes Mellitus (GDM) is diabetes first recognized during pregnancy that is not clearly pre-existing diabetes.
It usually develops in the second or third trimester.
Pregnancy causes increasing insulin resistance due to placental hormones.
GDM occurs when pancreatic insulin secretion cannot adequately compensate.
Most women with GDM are asymptomatic.
Risk factors include previous GDM, obesity, family history of diabetes, previous macrosomia, and polycystic ovary syndrome.
The 75-g oral glucose tolerance test (OGTT) is widely used for diagnosis.
Using IADPSG/WHO-based criteria, one abnormal OGTT value can establish the diagnosis.
Initial management includes nutrition therapy, appropriate physical activity, and glucose monitoring.
Insulin is the preferred medication when lifestyle measures are insufficient.

American Diabetes Association Professional Practice Committee. 15. Management of Diabetes in Pregnancy: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1). Diabetes Care .
American College of Obstetricians and Gynecologists. Gestational Diabetes Mellitus: Practice Bulletin No. 190 . Obstet Gynecol. 2018;131(2):e49-e64.
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Gestational Diabetes . National Institutes of Health.
World Health Organization. Diagnostic Criteria and Classification of Hyperglycaemia First Detected in Pregnancy . WHO.
International Association of Diabetes and Pregnancy Study Groups Consensus Panel. International Association of Diabetes and Pregnancy Study Groups Recommendations on the Diagnosis and Classification of Hyperglycemia in Pregnancy. Diabetes Care. 2010;33(3):676-682. Diabetes Care .
McIntyre HD, Catalano P, Zhang C, Desoye G, Mathiesen ER, Damm P. Gestational diabetes mellitus. Nat Rev Dis Primers. 2019;5:47. Nature Reviews Disease Primers .