A significant number of pregnant women develop high levels of blood glucose levels, called Gestational Diabetes Mellitus (GDM), which make them prone to develop a number of complications during pregnancy and parturition, putting the fetus also at risk. Let’s see what the GDM is and how do we manage it!
GDM: Quick overview
What is Gestational Diabetes Mellitus (GDM)?
Gestational diabetes mellitus is defined as an abnormal glucose tolerance that first begins or is recognized during pregnancy.
In most cases, GDM develops because the body is unable to increase insulin secretion adequately to compensate for the natural insulin resistance induced by pregnancy. Pregnancy is considered a physiologically stressful condition where the needed increase in insulin may not occur proportionately to overcome hormone resistance.
Does GDM mean I had diabetes before pregnancy?
Not usually. While this definition includes a few patients who might develop Type 1 diabetes during pregnancy or who had unknown pre-existing Type 2 diabetes (which may not remit after pregnancy), in the majority of cases, GDM develops during pregnancy itself. It is also possible that pregnancy simply unmasks an underlying tendency for glucose intolerance that may become evident later in life.
Who is at risk for developing GDM?
Several factors are associated with a higher risk of developing gestational diabetes:
• Body mass index (BMI) over 30 \text{ kg/m}^2.
• Previous gestational diabetes.
• Having previously delivered a macrosomic baby (weighing ).
• A family history of diabetes (specifically, a first-degree relative with diabetes).
• Family origin from populations with a high prevalence of diabetes, such as South Asian (specifically women whose family origin is India, Pakistan or Bangladesh), Black Caribbean, or Middle Eastern.
When and how is GDM diagnosed?
Screening for GDM is recommended for all asymptomatic pregnant women after 24 weeks’ gestation, typically between 24 and 28 weeks. Glucose values considered diagnostic of GDM are lower than those used for non-gestational diabetes.
A common approach involves a two-stage testing strategy:
1. Screening Test: A 50-gram oral glucose load is administered, without regard to the time of day or the last meal. Venous plasma glucose is measured 1 hour later. A value of () or above indicates the need for the diagnostic test.
2. Diagnostic Test: If the screening test is abnormal, a 100-gram oral glucose tolerance test (OGTT) is performed. This test is done in the morning after an overnight fast. Blood glucose is measured fasting and at 1, 2, and 3 hours. The diagnosis is made when two or more of the specific venous plasma concentrations are met or exceeded.
What are the main concerns associated with GDM during pregnancy?
The main concern in women diagnosed with GDM is excessive fetal growth, which can lead to increased maternal and perinatal morbidity. This overgrowth is often referred to as macrosomia.
Specific complications include:
• Shoulder dystocia. This occurs more frequently in infants of diabetic mothers because of fetal overgrowth and increased fat deposition on the shoulders.
• Increased likelihood of Cesarean delivery.
• Increased risk of preeclampsia and pregnancy-induced hypertension.
It is important to note that adverse pregnancy outcomes appear to occur along a continuum of glucose intolerance, even if the formal diagnosis of gestational diabetes is not assigned.
How is GDM treated and managed?
The overall aim of management is to normalize maternal blood glucose concentrations and thereby reduce the risk of excessive fetal growth.
1. Dietary and Lifestyle Changes: The first element of management is dietary modification, specifically by reducing the consumption of refined carbohydrate. Women should receive nutrition counseling. Intensive therapy with dietary modifications (and/or insulin therapy) has been shown to decrease rates of shoulder dystocia, macrosomia, and preeclampsia.
2. Blood Glucose Monitoring: Women with GDM should regularly self-monitor their blood glucose before and after meals. Capillary blood glucose levels should ideally be checked four times per day (once fasting and three times after meals).
3. Target Goals: Goals for blood glucose levels typically aim for:
◦ Fasting blood glucose levels of ().
◦ 1-hour post-prandial level of ().
◦ 2-hour post-prandial level of less than ().
4. Medication: If elevated glucose levels persist (especially fasting hyperglycemia), medications are typically initiated. Insulin has historically been considered the standard medication used to achieve glycemic control. While oral agents like glyburide and metformin have been studied, the current standard of care is insulin, unless circumstances prevent its use, in which case metformin is a reasonable alternative choice.
What happens after the baby is delivered?
Immediately after delivery, maternal glucose usually returns to pre-pregnancy levels.
However, even if glucose tolerance returns to normal postpartum, women who have had GDM are at an increased risk for developing Type 2 diabetes later in life. At least 50% of these women are diagnosed with overt diabetes at some point, with a 5-year risk estimated between 15% and 50%.
What follow-up is needed after pregnancy?
Due to the increased risk of developing Type 2 diabetes, follow-up screening is essential.
• Women should be screened for overt diabetes at 6–12 weeks postpartum using a fasting plasma glucose test or a 2-hour oral glucose tolerance test.
• In the UK, it is currently recommended that women have a fasting blood glucose measured at 6 weeks post-partum and have HbA1c concentrations measured annually to screen for the development of diabetes.
• All women who have had GDM should be provided with diet and lifestyle advice to reduce their future risk of developing Type 2 diabetes.