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Gestational Diabetes Mellitus: What It Is, Why Does It Happen, Diagnosis, Complications, Management and Prevention


Gestational Diabetes Mellitus: What It Is, Why Does It Happen, Diagnosis, Complications, Management and Prevention

December 19, 2021 | 6 min read

Gestational diabetes mellitus is a common condition that occurs during pregnancy specifically diagnosed in the third trimester of pregnancy. As the name suggests it essentially is similar to diabetes mellitus. A woman with gestational diabetes mellitus has hyperglycemia (high blood glucose levels) and problems with insulin resistance.

Normally during pregnancy, there is beta-cell hyperplasia. These are cells in the pancreas that produce and secrete the hormone insulin. When a pregnant lady eats a meal, her blood glucose rises and there is hyperglycemia. Hyperglycemia stimulates the beta cells of the pancreas to release the hormone insulin into the circulation.

The increase in insulin in the circulation then targets specific cells causing these cells to take up glucose from the blood in an attempt to reduce blood glucose levels. There is still enough blood glucose available in the circulation to enter fetal circulation. The fetus requires glucose in order to gain energy and grow. The fetus receives adequate glucose and so there is normal fetal growth.

During pregnancy, insulin sensitivity decreases. This means that the effects of insulin on maternal tissue are reduced. As the effect of insulin is reduced, there will be more glucose in the blood. Beta-cell hyperplasia in the maternal pancreas occurs because of reduced insulin sensitivity in maternal tissues.

In gestational diabetes, there is insulin resistance and therefore blood glucose is not taken up into maternal tissue as efficiently. The result of insulin resistance is hyperglycemia in the maternal circulation. The hyperglycemia also reaches the fetal circulation. This results in an increase in blood glucose in the fetus. This in turn stimulates the fetal pancreas to produce more insulin. With more fetal insulin the fetal tissue will take up more glucose that is available. So the growth of the fetus increases and you get a big baby.

The reason for a large decrease in insulin sensitivity and the development of insulin resistance in gestational diabetes is thought to be due to the placenta producing hormones such as estrogen, cortisol, and human placental lactogen causing a decrease in insulin sensitivity. These hormones produced during the late stages of pregnancy block the action of insulin resulting in insulin resistance.


Gestational diabetes is rather asymptomatic.

Risk factors

1.  Pregnancy at age greater than 35 years

2.  Obesity

3.  Family history of gestational diabetes mellitus

4.  Polycystic Ovary Syndrome (PCOS)

5.  Certain ethnic groups like African- Americans, Asians including Southeast Asians

6.  A previous history of gestational diabetes mellitus


The diagnosis of gestational diabetes is done during screening at 24 to 28 weeks of gestation. This is done with a fasting blood glucose or with the oral glucose tolerance test. A fasting blood glucose is measured between weeks 24 to 28 weeks. Fasting blood glucose of greater than 95 mg/dl (5.3 mmol/l) can help diagnose gestational diabetes mellitus.

Diagnosis of gestational diabetes mellitus is confirmed with an oral glucose tolerance test (GTT). A GTT is usually done if the blood glucose levels are greater than 190 mg/dl after a glucose challenge test. If blood glucose is greater than 180 mg/dl (10 mmmol/l) after one hour or greater than 155 mg/dl (8 mmol/l) after 2 hours of drinking the glucose solution.

These values normally should be lower because insulin should be lowering blood glucose. But with insulin resistance, blood glucose takes a lot longer to go down after eating. If one of the results of the GTT is higher than normal, the test is repeated after 4 weeks.


Maternal complications include:

1.  Hypertensive disorders like preeclampsia and eclampsia

2.  Increased risk for C- section due to large baby or hypertensive complications

3.  There is a 50% risk of developing type 2 diabetes in the future

Complications affecting your baby:

1.  Large baby – A baby with a higher than average birth weight

2.  Preterm birth – The baby is born before the due date because of early labor due to high blood glucose levels

3.  Respiratory distress syndrome – This is a serious condition where the newborn faces difficulty breathing. Babies born to mothers with gestational diabetes mellitus are at a higher risk of developing respiratory distress syndrome.

4.  Hypoglycemia – Sometimes babies born to mothers with gestational diabetes mellitus experience low blood sugar (hypoglycemia) where you get insulin-related hypoglycemia. Complications occur as a consequence of fetal hyperglycemia. Babies may experience seizures because of their low blood sugar levels. Prompt feeding or intravenous glucose infusion help to bring glucose levels back to normal.

5.  Stillbirth – Babies of mothers with untreated gestational diabetes mellitus may not survive delivery or die shortly before delivery.

6.  Obesity and type 2 diabetes – These babies have a higher risk of developing obesity and type 2 diabetes later in life.

7.  Other complications that may occur include hyperbilirubinemia (jaundice in the newborn) and hypocalcemia (low calcium levels). These complications if not adequately treated can cause brain damage in the child.

Management of Gestational Diabetes Mellitus

Managing the pregnancy itself and managing the baby after delivery involves a multidisciplinary team where the obstetrician plays a vital role. A woman with gestational diabetes is a high-risk patient.

The first line of management is diet and exercise. Medication including insulin or metformin is recommended if this fails. If the mother prefers, insulin injections can be used to manage gestational diabetes.

Pregnant women need to continuously monitor their blood glucose with a finger prick test -at least four times a day. It is important to monitor a growing fetus using ultrasound to detect any anatomical changes, to check for fetal size, fetal blood flow, and fetal heart rate.

The management of the baby occurs postpartum after delivery. It includes oxygenation because of the risk of respiratory distress syndrome, and management of hypoglycemia if present. It is also important to monitor the bilirubin, glucose, and calcium levels continuously.

Prevention of Gestational Diabetes Mellitus

Complete prevention of gestational diabetes mellitus is not a guarantee but adopting healthy choices before and during pregnancy can certainly decrease your chances of developing it. This is especially important if you have a history of gestational diabetes mellitus. It will reduce your risk of developing type 2 diabetes in the future.

1.  Eat healthy – Eating a whole food diet comprised of foods that are high in fiber and nutrients is good for your health and helps to regulate your blood sugar levels more effectively.

2.  Be physically active – Getting at least 30 minutes of exercise during and before pregnancy can protect you from gestational diabetes mellitus. A brisk walk, cycling, or swimming are some of the activities that are good options.

3.  Be at a healthy weight before getting pregnant – Lose the excess weight before getting pregnant. This can help you from developing several complications during pregnancy.

4.  Don’t gain too much weight during pregnancy – Gaining some weight is normal and healthy. However, gaining too much weight too quickly above the recommended range can increase your risk for gestational diabetes mellitus.

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