In diabetic pregnancy, perinatal mortality has decreased 30-fold since the discovery of insulin in 1922 and the introduction of intensive obstetrical and infant care in the 1970s. Nevertheless, the current perinatal mortality rates among women who are diabetic remain approximately twice those observed in the nondiabetic population.
Congenital malformations, respiratory distress syndrome (RDS), and extreme prematurity account for most perinatal deaths in contemporary diabetic pregnancies (see the table below).
|Morbidity||Gestational Diabetes||Type 1 Diabetes||Type 2 Diabetes|
Adapted from California Department of Health Services, 1991.
Injuries of birth, including shoulder dystocia and brachial plexus trauma, are more common among infants of diabetic mothers, and macrosomic fetuses are at the highest risk.
Most of the birth injuries occurring to infants of diabetic mothers are associated with difficult vaginal delivery and shoulder dystocia. Although shoulder dystocia occurs in 0.3-0.5% of vaginal deliveries among healthy pregnant women, the incidence is 2- to 4-fold higher in women with diabetes. Common birth injuries associated with diabetes are brachial plexus injury, facial nerve injury, and cephalohematoma. With strict glycemic control, the birth injury rate has been shown to be only slightly higher than controls (3.2 vs 2.5%).
Currently, clinical ability to predict shoulder dystocia is poor. Warning signs during labor (labor protraction, suspected fetal macrosomia, need for operative vaginal delivery) successfully predict only 30% of these events.
A central venous hemoglobin concentration greater than 20 g/dL or a hematocrit value greater than 65% (polycythemia) is not uncommon in infants of diabetic mothers and is related to glycemic control. Hyperglycemia is a powerful stimulus to fetal erythropoietin production, mediated by decreased fetal oxygen tension. Untreated neonatal polycythemia may promote vascular sludging, ischemia, and infarction of vital tissues, including the kidneys and central nervous system.
Approximately 15-25% of neonates delivered from women with diabetes during gestation develop hypoglycemia during the immediate newborn period.Neonatal hypoglycemia is less frequent when tight glycemic control is maintained during pregnancy and in labor. Unrecognized postnatal hypoglycemia may lead to neonatal seizures, coma, and brain damage.
Up to 50% of infants of diabetic mothers have low levels of serum calcium (< 7 mg/100 mL). These changes in calcium appear to be attributable to a functional hypoparathyroidism, though the exact pathophysiology is not well understood. With improved management of diabetes in pregnancy, the rate of neonatal hypocalcemia has been reduced to 5% or less.
Hyperbilirubinemia occurs in approximately 25% of infants of diabetic mothers, a rate approximately twice that in a healthy population. The causes of hyperbilirubinemia in infants of diabetic mothers are multiple, but prematurity and polycythemia are the primary contributing factors. Increased destruction of red blood cells contributes to the risk of jaundice and kernicterus. Treatment of this complication is usually with phototherapy, but exchange transfusions may be necessary if bilirubin levels are markedly elevated.
The nondiabetic fetus achieves pulmonary maturity at a mean gestational age of 34-35 weeks. By 37 weeks' gestation, more than 99% of healthy newborn infants have mature lung profiles as assessed by phospholipid assays. However, in a diabetic pregnancy, the risk of respiratory distress may not pass until after 38.5 gestational weeks.
Until recently, neonatal respiratory distress syndrome was the most common and serious morbidity in infants of diabetic mothers. In the 1970s, improved prenatal maternal management for diabetes and new techniques in obstetrics for timing and mode of delivery resulted in a dramatic decline in its incidence, from 31% to 3%. Nevertheless, respiratory distress syndrome continues to be a relatively preventable complication.
The majority of the literature indicates a signiﬁcant biochemical and physiologic delay in infants of diabetic mothers. Tyden et al and Landon and colleaguesreported that fetal lung maturity occurred later in pregnancies with poor maternal glycemic control, regardless of class of diabetes.
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