These unexplained stillbirths are associated with poor glycemic control. Lauenborg and coworkers (2003) identiied suboptimal glycemic control in two thirds of unexplained stillbirths between 1990 and 2000. Also, fetuses ofdiabetic mothers often have elevated lactic acid levels. Salvesen and colleagues (1992, 1993) analyzed fetal blood samples and reported that mean umbilical venous blood pH was lower in diabetic pregnancies and was signiicantly related to fetal insulin levels. Such indings support the hypothesis that hyperglycemia-mediated chronic aberrations in oxygen and fetal metabolite transport may underlie these unexplained fetal deaths (Pedersen, 1977).
Aside from hyperglycemia alone, maternal ketoacidosis can cause fetal death. Explicable stillbirths due to placental insufficiency also occur with increased frequency in women with overt diabetes, usually in association with severe preeclampsia. In the prior California study of nearly a halfmillion singleton deliveries, the fetal death risk was sevenfold higher in women with hypertension and pregestational diabetes compared with the threefold increased risk associated with diabetes alone (Yanit, 2012). Stillbirth rates are also greater in women with advanced diabetes and vascular complications.
Hydramnios. Diabetic pregnancies are oten complicated by excess amnionic fluid. According to Idris and coworkers (2010), 18 percent of 314 women with pregestational diabetes were identified to have hydramnios, deined as an amnionic fluid index (AFI) >24 cm in the third trimester. And, women with elevated HbA)c values in the third trimester were more likely to have hydramnios. A likely-albeit unproven-explanation is that fetal hyperglycemia causes polyuria (Chap. 11, p. 228). In a study from Parkland Hospital, Dashe and colleagues (2000) found that the API parallels the amnionic luid glucose level among women with diabetes. Further support for this association was provided by Vink and associates (2006), who linked poor maternal glucose control to macrosomia and hydramnios.
Neonatal Efects. Before tests of fetal health and maturity became available, delivery before term was deliberately selected for women with diabetes to avoid unexplained stillbirth. Although this practice has been abandoned, a higher frequency of preterm delivery in women with diabetes persists. Most are indicated deliveries due to advanced diabetes with superimposed preeclampsia. hat said, Little and associates (2015) in their analysis of early-term delivery (37°/7 to 386/7 weeks) found a 13-percent reduction in such deliveries in women with diabetes between 2005 and 2011.
Although modern neonatal care has reduced neonatal death rates due to immaturity, neonatal morbidiy due to preterm birth continues to be a serious consequence. In one Neonatal Research Network study of 10,781 extremely preterm neonates, those born to diabetic women treated with insulin prior to pregnancy were at greater risk for necrotizing enterocolitis and late-onset sepsis than neonates of mothers without diabetes (Boghossian, 2016).
Respiratory Distress Syndrome. Gestational age rather than overt diabetes is likely the most significant factor associated with respiratory distress syndrome (Chap. 33, p. 619). Indeed, in one analysis of 19,399 very-Iow-birthweight neonates delivered between 24 and 33 weeks' gestation, rates of respiratory distress syndrome in newborns of diabetic mothers were not higher compared with rates in neonates of nondiabetic mothers (Bental, 2011).