What are the risks to the pregnancy due to diabetes?

Maternal complications consist of hypertension, pre-eclampsia, increased risk of cesarean delivery, and development of diabetes mellitus after pregnancy. Fetal complications include macrosomia, neonatal hypoglycemia, polycythemia, increased perinatal mortality, congenital malformation, hyperbilirubinemia, respiratory distress syndrome, and hypocalcemia. Long-term consequences of macrosomia include increased risk of glucose intolerance, diabetes, and obesity in childhood.

The Australian Carbohydrate Intolerance Study in Pregnant Women (ACHOIS) was a large randomized control trial that investigated the role of screening and treatment of gestational diabetes in reducing perinatal complications, improving maternal outcomes, and affecting quality of life.

This trial of 1000 participants showed a composite reduction in serious perinatal morbidity and mortality (death, shoulder dystocia, bone fracture, and nerve palsy) in the intervention group compared to the conventional group. Also, a decrease in prevalence in macrosomia in the intervention group infants and reduced rate of gestational hypertension in the intervention group was found. Another large, multicenter randomized controlled trial conducted in the United States recruited women with mild gestational diabetes mellitus. One group received treatment consisting of dietary changes, self-monitoring of blood glucose and insulin if needed and the other received the usual prenatal care. Outcomes with respect to perinatal and obstetrical outcomes were compared.

This trial of 19,665 participants used slightly different parameters to diagnose gestational diabetes mellitus but had similar outcomes. There was a significant reduction in macrosomia with the treatment group as well as reduction in rates of cesarean delivery, shoulder dystocia, pre-eclampsia or gestational hypertension and weight gain. Finally, the HAPO (Hyperglycemia and Adverse Pregnancy Outcomes) trial, which included over 23,000 pregnant women, sought to clarify risks of adverse outcomes associated with various degrees of maternal glucose intolerance less severe than overt diabetes mellitus. The study results showed positive linear correlations between increasing levels of fasting, 1-hour and 2-hour plasma glucose after oral glucose tolerance testing (OGTT), and macrosomia and cord- blood C-peptide levels above the 90th percentile. Weaker associations were noted between glucose levels and cesarean delivery and neonatal hypoglycemia. The secondary outcomes of premature delivery, shoulder dystocia, hyper-bilirubinemia, and pre-eclampsia were also noted to increase in incidence with higher levels of post OGTT glucose levels.

The HAPO trial showed that maternal, fetal, and neonatal outcomes increased significantly with maternal hyperglycemia even at lower threshold ranges than prior diagnostic criteria for GDM. This prompted the International Association of Diabetes and Pregnancy Study Groups (IADPSG), whose committee consists of members from US and International diabetes organizations, including American Diabetes Association (ADA), and obstetrical organizations, to revise recommendations for diagnosing GDM. Whereas previously in the 2005 Fifth International Workshop-Conference on Gestational Diabetes Mellitus screening was based on risk stratification, now the IADPSG along with the ADA recom- mend that all women with no prior history of diabetes undergo 75-g glucose oral glucose tolerance test (OGTT) at 24–28 weeks gestation. Race also influences many complications of diabetes mellitus in pregnancy. For instance, black women have been shown to have lower rates of macrosomia, despite similar levels of glycemic control. Conversely, Hispanic women have higher rates of macrosomia and birth injury than women of other ethnicity, even with aggressive management. Infants of mothers with preexisting diabetes (T1 or T2) experience double the risk of serious injury at birth, triple the likelihood of cesarean delivery, and quadruple the incidence of newborn intensive care unit (NICU) admission. Studies indicate that the risk of these morbidities is directly proportional to the degree of maternal hyperglycemia.