A Clinical Overview of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is characterized by abnormal glucose tolerance that arises during pregnancy and is linked to various obstetric and neonatal complications, particularly higher infant birthweights. It is also recognized as a risk factor for future cardiometabolic diseases in both mothers and their offsprings. The prevalence of GDM is increasing globally due to rising rate of obesity among women of reproductive age, older maternal age, and changes in diagnostic criteria. There is scarcity of an international consensus on GDM diagnosis, reflecting its complex history and resource considerations in antenatal care. 

Contemporary clinical management of GDM should consider both immediate and long-term effects, as recent research showed that maternal hyperglycemia can lead to fetal overgrowth before the traditional diagnosis timeframe and has lasting impacts on the metabolic health of children and adolescents. This underscores the importance of identifying GDM as an early indicator of risk for type 2 diabetes and cardiovascular diseases, necessitating a broader clinical approach to address the long-term complications for both mothers and their offspring.

The HAPO study (2008) aimed to establish a relationship between glucose levels during pregnancy and outcomes in gestational diabetes mellitus (GDM). The study involved over 25,000 pregnant women and assessed glucose levels during a 75-g 2-hour OGTT at 24 to 32 weeks of gestation.Primary outcomes included high birthweight, cesarean delivery, neonatal hypoglycemia, and elevated cord blood C-peptide levels. While secondary outcomes included preeclampsia, preterm delivery, shoulder dystocia, hyperbilirubinemia, and NICU admission. The results of the study indicated a continuous positive correlation between maternal glucose levels and primary outcomes, with no specific glucose thresholds identified for increased complications.

Following HAPO, the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) revised GDM diagnostic criteria based on average glucose levels associated with increased risk.

• The IADPSG recommended a single elevated glucose level for GDM diagnosis, reflecting comparable risk levels.
• Universal testing for GDM is recommended by IADPSG and WHO for all pregnant women between 24 to 28 weeks using the 75-g 2-hour OGTT.
• National Institutes of Health (NIH) and the American College of Obstetricians and Gynecologists (ACOG) advocate for a 2-step testing approach, starting with an initial screening followed by a diagnostic OGTT for those who screen positive.
• The UK NICE guidelines suggest a selective screening approach based on risk factors, with higher diagnostic glucose thresholds than those set by IADPSG.

Source: Sweeting A, Wong J, Murphy HR, Ross GP. A Clinical Update on Gestational Diabetes Mellitus. Endocr Rev. 2022 Sep 26;43(5):763-793. doi: 10.1210/endrev/bnac003. PMID: 35041752; PMCID: PMC9512153.