Gestational Diabetes (GDM) Diagnosis and Screening

Gestational diabetes diagnosis is made at 24 to 28 weeks of gestation. Screening for gestational diabetes is recommended for all pregnant females regardless of their risk factors for developing GDM.

Gestational Diabetes or GDM is diabetes developing during pregnancy. Women with Type 1 or Type 2 Diabetes Mellitus who become pregnant are not labeled as having GDM. GDM or Gestational diabetes mellitus, as the name suggests, is a new onset of diabetes during gestation (pregnancy).

Gestational Diabetes is a condition that is associated with severe fetal and maternal complications. Hence, early recognition and treatment are very important.

Maternal complications of GDM include:

• repeated urinary tract infections,
• hypertension,
• preeclampsia, and
• hydramnios (oligo or polyhydramnios).

It also increases the risk of future operative complications [Ref].

What are the two different types of Gestational Diabetes Mellitus?

GDM is classified as A1GDM or A2GDM based on whether the pregnant female requires medical treatment or not.

Females who achieve their target blood glucose levels only with diet and lifestyle interventions are said to have A1GDM. Those females who require medical treatment in the form of drugs or insulin are labeled as A2GDM.

Gestational Diabetes Screening:

The symptoms of diabetes during pregnancy may be missed especially during the early stages when the blood sugars are slightly elevated.

Undiagnosed gestational diabetes may result in serious maternal and fetal complications. The ADA, therefore, recommends screening all pregnant females for gestational diabetes.

Universal Screening for GDM is recommended: All pregnant females should be screened for GDM

The ADA (American Diabetes Association) and the IADPSG (International Association of Diabetes and Pregnancy Study Group) recommend screening all pregnant patients on their first prenatal visit. All pregnant females should undergo fasting, random, and A1C testing during their first prenatal visit.

Females who do not fulfill the criteria of overt diabetes and have fasting blood glucose levels exceeding 92 mg/dl are labeled as GDM. If the fasting blood glucose level is less than 92 mg/dl, screening with a 72 gms oral glucose tolerance test is recommended at 24 to 28 weeks of gestation.

Screening is generally recommended at 24 to 48 weeks of gestation

Who is at risk of developing GDM (gestational diabetes)?

Screening for GDM is now recommended for all pregnant females. However, it is important to know the risk factors for developing gestational diabetes mellitus.

Previously, the ADA recommended screening for GDM only in the following situations:

All pregnant females who are overweight or obese, and have one of the following risk factors were candidates for screening for GDM:

• Females who are inactive most of the time,
• Pregnant females with a first-degree relative who has diabetes
• Asians or other high-risk ethnic groups
• Females who have delivered a child weighing 4 kgs or more,

• Females with a history of:

  • gestational diabetes or gestational hypertension,
  • preeclampsia,
  • eclampsia, or HELLP (hemolysis, elevated liver enzymes, and low platelets) in the previous pregnancy
• HDL (High-density lipoprotein) less than 35 mg/dl
• TGL (Triglyceride levels exceeding 250 mg/dl)
• Females with a history of polycystic ovarian syndrome
• NASH (non-alcoholic fatty liver disease)
• Glycated hemoglobin of 5.7% or more
• Females with impaired fasting or impaired glucose tolerance test
• Females with a medical condition linked with insulin resistance such as acanthosis nigricans
• History of cardiovascular diseases
• Obese females with a BMI exceeding 30 kg/m² before pregnancy or excessive weight gain during the first 24 weeks of pregnancy
• Pregnant females who are older than 40 years of age

Gestational Diabetes Diagnosis:

There are different guidelines that differ in their cut-off values for labeling a pregnant female as having GDM. No criteria have been validated in clinical trials.

GDM can be diagnosed using one-step or two-step glucose-tolerance tests. The summary and cut-off values are presented here:

Ones step ADA criteria for the Diagnosis of GDM (Gestational diabetes mellitus):

Females are labeled as GDM if more than one of the following blood sugar readings are elevated at 24 to 28 weeks of gestation. Patients are given 75 gms of anhydrous glucose in 200 to 300 ml of water.

Blood sugars before administration, one hour after administration, and two hours after glucose administration are measured.

The ACOG two-step approach for the diagnosis of GDM:

The American College of Obstetrics and Gynecologists’ two-step approach is used to diagnose GDM regardless of the timings of the day.

STEP 1 of ACOG Criteria:

Females are given 50 gms of glucose and blood or plasma sugars are measured at one hour:

STEP 2 of ACOG Criteria:

In STEP 2 of the ACOG Criteria, females are given 100 gms of oral glucose after an overnight fast of at least 8 hours. If two or more values are in the following ranges, the person is labeled GDM.

Females who have a positive GTT early in pregnancy are labeled as having T2DM. Those with a negative OGTT are screened again at 24 to 28 weeks of gestation.

If the test is negative at 24 to 28 weeks, the diagnosis of GDM is ruled out. If positive, females are labeled to have GDM.

WHO Criteria of GDM (Gestational diabetes mellitus):

The WHO criteria for the diagnosis of GDM has been last revised in 2013. Pregnant females are labeled as GDM patients if they have any of the following readings:

• Fasting Plasma glucose: 92 mg/dl (5.1 mmol/L) or more
• 2 hours post-prandial glucose: 153 mg/dl (8.5 mml/L) or more

Canadian Diabetes Association Criteria for gestational diabetes mellitus [Ref]:

The Canadian Guidelines recommend two approaches. A two-step approach in which females are given 50 gm of oral glucose in the first step.

If any of the following readings are abnormal, the 50 gm OGTT is followed by a 75 gms oral glucose tolerance test. One or more abnormal readings are diagnostic of Gestational Diabetes Mellitus.

STEP 1:

STEP 2:

IADPSG criteria for the diagnosis of GDM:

The IADPSG criteria for the diagnosis of GDM is the same as the ADA.

Females are labeled as GDM if more than one of the following blood sugar readings are elevated at 24 to 28 weeks of gestation. Patients are given 75 gms of anhydrous glucose in 200 to 300 ml of water.

Blood sugars before administration, one hour after administration, and two hours after glucose administration are measured.

NICE Criteria of Gestational Diabetes Diagnosis:

NICE GDM criteria were last revised in 2015. Pregnant females are labeled as GDM if they have any of the following blood glucose readings:

• Fasting Plasma glucose: 100 mg/dl (5.6 mmol/L) or more
• 2 hours post-prandial glucose: 140 mg/dl (7.8 mml/L) or more

In Summary:

Gestational diabetes diagnosis is important to prevent fetal and maternal complications. Since females may be asymptomatic, screening for gestational diabetes is mandatory for all pregnant females. Screening should be done at the first antenatal visit and 24 to 28 weeks of gestation.

Most guidelines (ADA, WHO, and IADPSG) recommend a cut-off for the fasting plasma glucose to be no more than 92 mg/dl. The ACOG recommends a cut-off for the fasting plasma glucose of 95 mg/dl or less.