DIABETES IN PATIENT SUBGROUP Gestational diabetes Key points Yael R Lefkovits C Treatment of diabetes mellitus in pregnancy reduces the risk of Zoe A Stewart perinatal complications, including pre-eclampsia, pregnancy- induced hypertension, caesarean delivery, large for gestational Helen R Murphy age babies and neonatal adiposity in women with gestational diabetes mellitus (GDM) Abstract C There is inadequate evidence to recommend universal One in six live births occur in women with diabetes mellitus, of which screening for GDM across all countries. Screening should be the most common type, accounting for approximately 87.5% of all dia- tailored to the clinical and economic needs of the region betes in pregnancy, is gestational diabetes mellitus (GDM). Maternal hyperglycaemia is one of the principle determinants of maternal C Continuous glucose monitoring provides a direct measure of e fetal complications in pregnancy in GDM. In particular, hyperglycae- fetal exposure to maternal blood glucose concentrations and mia is most commonly associated with increased rates of instrumental will be used increasingly in research and in clinical practice and/or operative delivery, pre-eclampsia, increased adiposity, macro- somia and infant birthweight >90th percentile. Large for gestational C The potential benefits of oral hypoglycaemic agents (metfor- age infants have an increased risk of birth complications, including min, glibenclamide) should be weighed against their uncertain shoulder dystocia and stillbirth. Maternal hyperglycaemia is also one long-term risks on the developing fetus of the factors most amenable to treatment during pregnancy. For most women with GDM, dietary and lifestyle modifications are suffi- cient to achieve glycaemic targets and optimal pregnancy outcomes. This chapter summarizes the latest evidence-based recommendations diabetes. Risks to the offspring include increased adiposity, for the screening, diagnosis and treatment of pregnancies complicated macrosomia and birthweight that is large for gestational age by GDM. It considers the International Association of Diabetes and (LGA). Although serious perinatal complications such as death, Pregnancy Study Groups and the National Institute for Health and shoulder dystocia, bone fracture or nerve palsy are rare (1e4%), Care Excellence guidelines. The evidence in support of dietary inter- macrosomia (infant birthweight >4 kg) and LGA (birthweight ventions for antenatal management and treatment options for post- >90th percentile) are common, affecting 10e20% of neonates partum care are reviewed. born to women with GDM. Keywords Diabetes; gestational diabetes mellitus; hyperglycaemia The World Health Organization (WHO) has previously in pregnancy; large for gestational age; macrosomia; MRCP; defined GDM as any degree of hyperglycaemia (regardless of pregnancy severity) with an onset or first recognition during pregnancy. The International Association of Diabetes and Pregnancy Study Groups (IADPSG) now uses the term ‘overt diabetes’ to describe the phenomenon of severe hyperglycaemia appearing to mimic pre-existing diabetes. Introduction For all pregnant women, hyperglycaemia should be consid- ered as a continuous risk variable (like maternal weight and In the UK, an estimated 700,000 pregnancies are affected by blood pressure measurements), rather than being dichotomized diabetes mellitus per year, and 87.5% of these are classified as as normal or abnormal based on arbitrary diagnostic cut-offs. gestational diabetes mellitus (GDM). Worldwide it is estimated The recognition that the relationship between maternal blood that 1 in 6 live births occur in women with diabetes, causing glucose concentration and maternalefetal outcomes is a contin- challenges for low- and middle-income countries. For the uum has, however, created controversy regarding appropriate mother, GDM is associated with increased risk of pre-eclampsia, diagnostic thresholds. delivery by caesarean section and later development of type 2 Pathophysiology Yael Lefkovits is currently completing an MB BS(Hons) and BMedSc from A normal pregnancy is characterized by a progressive increase in Monash University in Australia and is an Associate Researcher at insulin resistance from the second trimester until delivery. It is University of Cambridge, UK. Competing interests: none declared. attributed to a variety of factors, including increased secretion of Zoe A Stewart MB BS PhD is an Honorary Clinical and Research human placental lactogen, growth hormone and cortisol during Fellow at the University of Cambridge, UK. Competing interests: pregnancy. A combination of increased maternal adiposity and none declared. insulin resistance both contribute to hyperglycaemia in women b Helen R Murphy MD FRACP is a Professor of Women’s Health at with inadequate pancreatic -cell function. King’s College London, Professor of Medicine (Diabetes and Antenatal Care) at the University of East Anglia, Norwich, and an Implications of GDM for pregnancy outcomes Honorary Consultant Physician at Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK. Competing interests: none Women diagnosed with GDM are more susceptible to pre- declared. eclampsia, caesarean section delivery, premature delivery and MEDICINE 47:2 114 Ó 2019 Elsevier Ltd. All rights reserved. DIABETES IN PATIENT SUBGROUP development of type 2 diabetes.1 Serious perinatal complications recommend the one-step approach at 24e28 weeks’ gestation. such as death, fetal organomegaly, shoulder dystocia, bone The NICE guidelines also advise early screening, as soon as fracture and nerve palsy are rare, complicating 1e4% of GDM possible after pregnancy is confirmed, for women with previous pregnancies. However, perinatal complications such as macro- GDM, either by self-monitoring of blood glucose (SMBG) or by a somia (infant birthweight >4 kg) and LGA infants are common, 75 g OGTT. The United States Preventive Services Task Force complicating 10e20% of these pregnancies. Macrosomic and (USPSTF) found evidence supporting screening of asymptomatic LGA infants have an increased risk of longer term insulin resis- pregnant women after 24 weeks of gestation but found there is tance, cardiovascular disease, obesity and diabetes, with female insufficient evidence to assess the balance of benefits and harms offspring having a higher chance of developing GDM during of screening before 24 weeks, gestation. future pregnancies. The Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Diagnosis of GDM study of >25,000 pregnant women confirmed that maternal The NICE guidelines recommend that GDM be diagnosed if glucose levels are directly associated with adverse pregnancy fasting glucose is 5.6 mmol/litre, or the 2-hour post-OGTT outcomes, independent of other risk factors such as maternal glucose is 7.8 mmol/litre. The IADPSG consensus panel rec- obesity.1 The even larger Indian Gestational Diabetes Prevention ommends a lower fasting glucose of 5.1 mmol/litre, a 1-hour and Control Project included >57,000 pregnant women. It also post-OGTT glucose of 10.0 mmol/litre or a 2-hour value of demonstrated that women with GDM had higher rates of 8.5 mmol/litre.3 The WHO and American Diabetes Association pregnancy-induced hypertension, preterm and caesarean de- (ADA) support the IADPSG diagnostic criteria. livery, and antepartum and postpartum haemorrhage, with It is worth noting that different populations of women mani- maternal and neonatal outcomes directly related to maternal fest different proportions of hyperglycaemia at each point of the blood glucose concentration. OGTT. For example, the IADPSG’s threshold for GDM (fasting glucose 5.1 mmol/litre) is reached by 25% of women with Risk factors for the development of GDM2 GDM in Hong Kong, yet in Barbados and the USA this figure was Risk factors are: closer to 75%. The reasons for this may be partially explained by a past history of impaired glucose tolerance or GDM differences in maternal age, BMI and family history of diabetes in maternal body mass index (BMI) >30 kg/m2 different populations, but the exact mechanism underlying this a family history of diabetes (particularly in a first-degree phenomenon remains unclear. relative) a previous LGA infant or infant >4.5 kg Monitoring hyperglycaemia in pregnancy an ethnic origin associated with a high prevalence of type 2 Management should be tailored to the personal preferences of the diabetes (e.g. Indian, Pakistani, Bangladeshi, Middle- woman with GDM. In general, women are advised to carry out Eastern, Caribbean). SMBG at least four times daily, most typically before breakfast The risk of GDM is increased when multiple risk factors are and at 1e2 hours after each of the main meals. present. Retrospective studies suggest increased risk in women The use of continuous glucose monitoring (CGM) has allowed with polycystic ovary syndrome, subfertility, long-term gluco- far greater insights into maternal blood glucose concentration corticoid use or conception via assisted reproductive technolo- during pregnancy, in particular, to quantify overnight and post- gies. However, 30e50% of affected women have no known risk prandial glucose excursions. Newer glucose monitoring systems, factors. which do not require SMBG, are becoming increasingly accurate, accessible and affordable. Evaluation of the use of the Abbott Screening for GDM Diabetes Care FreeStyle Libre flash glucose monitoring system in Early identification and intervention to reduce fetal exposure to pregnant women with diabetes found good