What Is Gestational Diabetes? Causes, Risk Factors, Diagnosis

A gestational diabetes diagnosis catches most women off guard. It often comes after an uneventful pregnancy and a test that seemed more like routine. If you have just received the diagnosis, you probably have two immediate questions: How did this happen, and what does it mean for me and my baby?

What Gestational Diabetes Is

Gestational diabetes (GDM) refers to a glucose tolerance disorder that is first detected during pregnancy. During pregnancy the body produces more hormones that counteract the effect of insulin — this is normal and beneficial, ensuring that sufficient nutrients are available to the baby. In some women, however, the pancreas cannot fully compensate for this increased insulin demand, causing blood glucose levels to rise.

Who Is at Increased Risk

According to the DDG practice recommendation, the most significant known risk factors include:

• Overweight and obesity before pregnancy (the risk increases continuously with every unit of BMI increase)
• Gestational diabetes in a previous pregnancy
• Diabetes in first-degree relatives
• Advanced maternal age
• Certain ethnic backgrounds, in particular South and East Asian and Middle Eastern origin
• Polycystic ovary syndrome (PCOS)

Important to know: many women with GDM have none of these risk factors. For this reason, screening is offered to all pregnant women regardless of their individual risk profile.

How Common Is Gestational Diabetes

Global studies show widely varying rates depending on the population studied, the testing method used, and the diagnostic thresholds applied. The range in the literature extends from below 2 percent to above 20 percent of all pregnancies; with today's common diagnostic criteria, many studies report figures in the mid-to-upper single digits or low double digits. Rates have risen noticeably in recent years, partly due to stricter diagnostic criteria and partly due to an increase in risk factors within the general population.

How the Diagnosis Is Made

The standard pathway is a two-step screening between weeks 24 and 28 of pregnancy: first a 50-gram screening test, followed by a diagnostic 75-gram oGTT if the result is abnormal. In certain high-risk situations, early screening in the first trimester may be appropriate. The exact procedure of the oGTT and which values are considered abnormal are explained in detail in the next article.

What the Diagnosis Does Not Mean

Gestational diabetes is not type 1 or type 2 diabetes and is in virtually all cases a temporary metabolic change that ends with delivery. It also does not automatically mean that insulin will be needed — the majority of women manage with dietary adjustments and physical activity. What it does mean is closer monitoring during pregnancy and sensible follow-up care afterwards, because the statistical risk of developing type 2 diabetes later in life is elevated.

This article does not replace medical advice. For questions about your individual diagnosis, please contact your treating practice.

Sources

Sources (secondary citations from the S3 guideline / DDG practice recommendation):

• Torloni MR, Betrán AP, Horta BL, et al. Prepregnancy BMI and the risk of gestational diabetes: A systematic review of the literature with meta-analysis. Obesity Reviews 2009;10(2):194–203.
• Sacks DA, Hadden DR, Maresh M, et al. Frequency of gestational diabetes mellitus at collaborating centers based on IADPSG consensus panel-recommended criteria: The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study. Diabetes Care 2012;35(3):526–8.
• Remaining risk factors: general consensus from S3 guideline Chapter 5 "Risk factors", no single study as sole source.