Mild Gestational Diabetes

Towards a Redefined Threshold?

Natasha L Hezelgrave; Daghni Rajasingham; Andrew H Shennan; M Regina Torloni

Expert Rev Endocrinol Metab. 2012;7(6):669-676.

Abstract and Introduction

Abstract

Gestational diabetes mellitus (GDM), the most common medical complication of pregnancy, is defined as carbohydrate intolerance resulting in hyperglycemia of variable severity with onset or first recognition during pregnancy. In reality, gestational diabetes mellitus is a spectrum of maternal hyperglycemia caused or exacerbated by pregnancy, in which blood glucose levels lie along a continuum, associated with a wide spectrum of metabolic abnormalities and conferring varying degrees of pregnancy-related risk. In recent years, the WHO diagnostic thresholds in current use have been called into question, as increasing evidence mounts that 'mild gestational diabetes' confers increased maternal and fetal risk, despite glucose levels falling below current thresholds. This review summarizes the existing evidence, unanswered questions and health service implications related to women with so-called 'mild' gestational diabetes.

Introduction

In parallel with the obesity epidemics, rates of gestational diabetes mellitus (GDM) are steadily rising in the developed world as well as in most low- and middle-income countries.^[1–4] This scenario, along with the well-documented adverse maternal–fetal outcomes associated with GDM,^[5] have fuelled the long-standing debate within the obstetric and endocrine community regarding optimal screening, diagnostic and treatment criteria for this disorder. Moreover, in recent years, several studies have suggested poorer maternal and fetal outcomes in pregnancies with lower levels of hyperglycemia, leading to questions regarding the currently used GDM diagnostic thresholds. The basic question in the current debate could be summarized as: does identifying and treating women with hyperglycemia falling below the current lower threshold – the so-called 'mild' gestational diabetes – confer benefit to mother or infant?

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Box 1. Maternal and perinatal risks associated with gestational diabetes.
Perinatal Macrosomia Polyhydramnios Shoulder dystocia and birth injuries Respiratory distress syndrome Neonatal metabolic disorders: hypoglycemia, hypocalcemia, hypomagnesemia and hyperbilirubnemia Increased perinatal mortality Maternal Preeclampsia Operative vaginal delivery Cesarean section Perineal lacerations Postpartum infection Preterm labor

Box 2. Diagnostic criteria for gestational diabetes mellitus ^†: recommendations of the IADPSG, based on second-trimester 75-g oral glucose tolerance test.
Fasting plasma glucose: 5.1 mmol/l (92 mg/dl) 1-h plasma glucose: 10.0 mmol/l (180 mg/dl) 2-h plasma glucose: 8.5 mmol/l (153 mg/dl)
^†If one or more of these is greater than or equal to these values. Data taken from [37].