In pregnancies complicated by diabetes mellitus, a key therapeutic goal during labor is to avoid maternal hyperglycemia, which increases the risk of fetal acidemia and neonatal hypoglycemia . Glucose management postpartum is less critical, but remains a concern because of the potential for maternal hypoglycemia. Postdelivery glucose management is challenging because of the large and rapid changes in maternal hormone concentrations after delivery of the placenta.
Maternal glucose concentration in the intrapartum period is affected by the mother's type of diabetes (type 1, type 2, or gestational) and the phase of labor that she is in (latent versus active). Women with type 1 diabetes mellitus have no endogenous insulin production, whereas those with type 2 and gestational diabetes generally have sufficient basal insulin secretion to avoid diabetic ketosis. The latent phase of labor is characterized by slow cervical change over hours, but the length varies greatly. When labor is induced, the latent phase may extend beyond 24 hours. The latent phase causes minimal change in maternal metabolic demands. In contrast, active labor is a period of relatively rapid cervical dilatation with fetal descent and, ultimately, delivery of the infant. It occurs over a few hours and should be viewed as intense exercise, with increased energy expenditure and decreased insulin requirements.
In this topic review, we will assume that women with diabetes have entered labor with well-controlled glucose levels during the antecedent pregnancy. Women with poorly controlled pregestational diabetes entering labor may require larger doses of insulin. Their newborns are likely to have severe and prolonged hypoglycemia secondary to pancreatic hyperplasia and hyperinsulinemia, which are manifestations of diabetic fetopathy. Maternal normoglycemia during labor in these cases cannot prevent neonatal hypoglycemia once fetal pancreatic hyperplasia and excessive in utero insulin secretion have been established in response to a prolonged period of antenatal hyperglycemia.
APPROACH TO INTRAPARTUM GLYCEMIC CONTROL
Most protocols for intrapartum management of diabetes rely on a combination of glucose and insulin infusion to maintain target glucose ranges. Clinical evidence does not support one intrapartum management protocol over another. This evidence is largely retrospective and derived primarily from women with type 1 diabetes, or from groups of women with both pre- and gestational diabetes treated with the same protocol, thus not accounting for the probable differences between women with different underlying metabolic disorders. In the absence of high quality evidence from well designed randomized trials, we will present the components of intrapartum glycemic management and provide sample protocols.
Three protocols are presented (table 1); protocols 1 and 2 are recommended by the American Diabetes Association Technical Reviews and Consensus Recommendations for Care . Protocols 1 and 2 were designed for women with pregestational diabetes, but can be used in women with gestational diabetes. The third protocol ("Rotating fluids protocol") is from a randomized clinical trial demonstrating efficacy in women with primarily gestational diabetes (and a small number with type 2 diabetes), and should not be used in women with type 1 diabetes .