Diagnosis And Testing For Gestational Diabetes: What You Need To Know

Diabetes is a condition that reduces your body’s ability to regulate blood sugar.

Gestational diabetes is a type of diabetes that only develops in pregnant women.

When you eat foods like potatoes, bread, rice, and fruit, your body breaks them down into an energy source called glucose (sugar). Your pancreas releases an enzyme called insulin to help your cells use glucose for energy. Insulin acts as a key to “unlock” glucose for your cells.

Insulin resistance is when your cells don’t respond well to insulin.

People with gestational diabetes cannot produce enough insulin to overcome insulin resistance during pregnancy. This causes glucose to build up in the bloodstream, leading to high blood sugar.

Gestational diabetes affects 2–10%¹ of pregnant women. It can create risks for you and your child, but you can successfully manage the condition by improving your diet and exercising more. You might also need treatment with supplemental insulin or metformin.

The condition will most likely stop affecting you after your baby is born. However, you will have a higher risk of developing type 2 diabetes later in life.

So how do you know if you have gestational diabetes? Find out when you might be tested and what a gestational diabetes test involves.

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What causes gestational diabetes?

A pregnant woman provides critical glucose nutrients to a growing fetus. To do this, the body develops a natural level of insulin resistance to ensure the fetus receives enough nutrients.

Women also gain extra weight during pregnancy, which increases insulin resistance. This development of insulin resistance during pregnancy sometimes triggers diabetes that lasts until the baby is delivered.

All women develop some level of insulin resistance during pregnancy. Those who develop gestational diabetes may already have prediabetes or certain risk factors that make them susceptible to type 2 diabetes. You can read more about risk factors below.

Who is at risk of gestational diabetes?

There are two types of diabetes.

Type 1 diabetes is a genetic autoimmune condition where the pancreas doesn’t make insulin (or makes very little). It usually develops in children, teenagers, and young adults, but the condition can appear at any age.

Type 2 diabetes usually appears in adults over 45, but it can affect younger people too. The condition is generally caused by lifestyle factors like diet, obesity, and a lack of exercise.

Some type 2 diabetes risk factors are the same for gestational diabetes. Most women who develop gestational diabetes will have one or more of the following risk factors:

  • Advanced maternal age (35 years and above

  • Obesity (BMI ≥30)

  • High blood pressure (pre-existing before pregnancy)

  • History of gestational diabetes (you had the condition in previous pregnancies)

  • Family history of type 2 diabetes

  • History of the polycystic ovarian syndrome (PCOS)

  • Hemoglobin A1C levels above 5.7%

  • You previously gave birth to a large baby (+8.8lbs or ≥4,000g)

  • Belonging to a “high-risk” ethnicity (Hispanic, Black, American Indian, or Asian American)

Your doctor will likely order a gestational diabetes test earlier than normal if you meet one or more of the above criteria.

What are the symptoms of gestational diabetes?

Many pregnant women with gestational diabetes have no noticeable symptoms. Others may not notice any due to overlapping pregnancy-related symptoms.

Gestational diabetes can also cause symptoms that are similar to those of type 2 diabetes, such as:

  • More frequent urination

  • Excessive thirst

  • Eyesight problems, such as blurry vision

  • Tingling in the hands or feet

  • Fatigue

  • Dry skin

  • Weight loss

  • Nausea

  • Increased yeast infections

Many pregnancy symptoms mirror those of gestational diabetes. This makes the condition easy to miss without routine testing.

How gestational diabetes is diagnosed

Most women in the US are tested for gestational diabetes between 24 and 28 weeks² of pregnancy. Your doctor may test you earlier than this if you have a higher risk due to any of the reasons above.

There are two types of testing available: one-step and two-step testing.

Two-step testing

Two-step testing involves:

  1. A glucose test (or glucose challenge test)

  2. A three-hour oral glucose tolerance test (OGTT)

Glucose test (or glucose challenge test)

Gestational diabetes causes a buildup of sugar in the bloodstream when you consume large amounts of carbohydrates or sugar. A 50g glucose challenge test assesses how your body copes after you consume a large amount of liquid sugar.

Your doctor will ask you to consume a sugary liquid. They will measure your blood glucose levels one hour after you consume the sugary liquid.

You won’t need to change your diet or fast to prepare for this test.

A high blood sugar readout suggests you have high insulin resistance, meaning your body cannot process glucose correctly.

Depending on factors such as the prevalence of gestational diabetes in your community, your doctor will use a threshold to interpret your 50g glucose challenge test results.

A reading higher than one of these thresholds³ may be considered abnormal:

  • 130 mg/dL (7.2 mmol/L)

  • 135 mg/dL (7.5 mmol/L)

  • 140 mg/dL (7.8 mmol/L)

Your doctor will recommend a 100g oral glucose tolerance test if your reading is equal to or higher than the threshold, but under 200 mg/dL (11.1 mmol/L).

Oral glucose tolerance tests (OGTT)

Your doctor may order a glucose tolerance test (sometimes called a three-hour glucose tolerance test) if your blood sugar levels come back as abnormal in your glucose challenge test. This test can confirm if you have gestational diabetes.

Unlike the glucose test, you will need to fast for at least eight hours to prepare for this test. This involves not eating food and only drinking a few sips of water.

Your doctor will draw your blood when you arrive for the test to assess your fasting blood sugar levels. You will then consume a sugary liquid glucose drink (100 g). This might make you feel nauseous, lightheaded, or sweaty, but side effects are generally rare. Some women compare the glucose drink to a very sweet soda.

You will then have your blood drawn periodically over the next few hours. Your doctor will compare your initial reading (your “fasting value”) with readings taken throughout the test.

You may have gestational diabetes if your blood sugar levels are high after consuming the sugary drink.

Here’s how your doctor may interpret your readings:

  • A fasting level of 95 mg/dL (5.3 mmol/L) or higher indicates diabetes

  • A one-hour glucose level of 180 mg/dL (10 mmol/L) or higher indicates diabetes

  • A two-hour glucose level of 155 mg/dL (8.6 mmol/L) or higher indicates diabetes

  • A three-hour glucose level of 140 mg/dL (7.8 mmol/L) or higher indicates diabetes

You can resume your normal routine straight after having this test.

One-step testing

One-step testing does not involve a glucose challenge test. Instead, you will need to visit your doctor for a two-hour glucose tolerance test. This test works similarly to the two-step test’s three-hour glucose tolerance test.

You will need to fast for at least eight hours before this test.

You will have your blood drawn when you arrive for your visit. Then you will be asked to consume a sugary glucose drink (75g). Your doctor will draw your blood twice more: 60 minutes after you consume the glucose drink and two hours afterward.

The thresholds for abnormal results are as follows:

  • A fasting level of 92 mg/dL (5.1 mmol/L)

  • A one-hour glucose level of 180 mg/dL (10 mmol/L)

  • A two-hour glucose level of 153 mg/dL (8.5 mmol/L)

What if I’m diagnosed with gestational diabetes?

Being diagnosed with gestational diabetes can be worrying. Untreated, it can impact you and your baby’s health.

Your doctor will discuss a treatment plan with you if they diagnose gestational diabetes. This may involve:

  • Glucose monitoring

  • Lifestyle changes, such as healthy eating and increased physical activity

  • Monitoring your baby’s growth and development

  • Medication, such as insulin or metformin

Be sure to attend all your prenatal appointments and follow your doctor’s advice carefully to help avoid complications.

The lowdown

Gestational diabetes is a type of diabetes that develops during pregnancy.

Most cases only last until shortly after the baby is delivered.

Women develop natural insulin resistance during pregnancy to facilitate the growth of the fetus, but this triggers diabetes in some women.

The condition does not usually cause symptoms.

Many women who develop gestational diabetes are already predisposed to type 2 diabetes through certain risk factors, such as obesity, a family history of diabetes, or belonging to a high-risk ethnic group. Other risk factors can trigger gestational diabetes, including having the condition during a previous pregnancy and giving birth to a large baby.

Most women are tested for gestational diabetes between 24 and 28 weeks of pregnancy. Your doctor will use one or two-step testing to assess your blood glucose levels. The two types of tests commonly used are the glucose test (glucose challenge) and the oral glucose tolerance test.

You will need to consume a sugary glucose drink during both of these tests and have your blood drawn. Your doctor will rule out or diagnose gestational diabetes depending on your blood sugar levels.

It’s possible to manage gestational diabetes through lifestyle changes, medication, and close monitoring.

  1. Gestational diabetes | Centers for Disease Control and Prevention

  2. Tests & diagnosis for gestational diabetes | NIH: National Institute of Diabetes and Digestive and Kidney Diseases

  3. Screening and diagnostic criteria for gestational diabetes melilitus | American Academy of Family Physicians

Other sources:

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