Complications Associated with Preexisting Diabetes

Complications associated with diabetes can adversely affect both the woman and fetus. The incidence of fetal complications is correlated with maternal glycemic control and the trimester of pregnancy.

10.4.2.1 Fetal

Congenital malformations and spontaneous abortions are associated with maternal hyperglycemia in the first 12 weeks of gestation. The central nervous system, heart, lungs, gastrointestinal tract, kidneys, urinary tract, skeleton, and placenta are all vulnerable to adverse effects (Table 10.1) [21-23]. The frequency and severity of complications decrease if maternal normoglycemia is maintained throughout pregnancy.

Second- and third-trimester fetal complications include macrosomia, neonatal hypoglycemia, neonatal hypocalcemia, hyperbilirubinemia, polycythemia, respiratory distress syndrome, preterm delivery, and stillbirth. With the exception of stillbirth, other complications are more closely associated with infant morbidity than mortality.

Macrosomia is the most common complication associated with diabetes and pregnancy, estimated at 20-45%, depending on the population [24, 25]. The definition of macrosomia varies and ranges from 4,000 to 4,500 g [26]. Macrosomia is thought to occur if maternal glycemic levels are elevated in the third trimester. Pedersen hypothesized that maternal hyperglycemia leads to fetal hyperglycemia, which stimulates the fetal pancreas to produce excessive insulin and results in excess growth [27]. Macrosomic infants have disproportional large fetal trunks in relation to their head size, thereby increasing the risk of difficult delivery, shoulder dystocia, brachial plexus palsy, or facial nerve injury.

Neonatal hypoglycemia is a fetal serum glycemic level <35 g/dl in the first 12 h of life. Maternal glucose transport abruptly ceases when the umbilical cord is clamped. If fetal hyperinsulinemia continues, the infant will experience a rapid decrease in glycemic levels. The preferred method of treatment is oral feeding, preferably with breast milk, and frequent blood glucose monitoring within the first 4-6 h of life. Respiratory distress syndrome is caused by a deficiency of surfactant, necessary for fetal lung maturity. Neonatal hypocalcemia is serum calcium <7 mg/dl. Hyperbilirubinemia occurs when the serum bilirubin level of the neonate >13 mg/dl. Polycythemia, which is a hematocrit >65% at delivery, could lead to perinatal asphyxia. The risk of these conditions decreases if the mother maintains optimal glycemic control throughout pregnancy.

Advances in diabetes research and management have led to decreased risks of stillbirth in infants born to women with preexisting diabetes, though it remains higher than in the general pregnant population. Maternal vascular complications, poor blood glucose control, and inadequate or no prenatal care are associated with higher rates of stillbirths in women with diabetes prior to pregnancy.

Table 10.1

Congenital Anomalies Associated with Preexisting Diabetes and Pregnancy

Central Nervous System

  • Neural tube defects (e.g., anencephaly, spina bifida, hydrocephalus)
  • Microcephaly
  • Dandy-Walker complex

Cardiovascular

  • Coarctation
  • Transportation of great vessels
  • Truncus arteriosus
  • Aortic stenosis

Gastrointestinal

  • Duodenal atresia
  • Anorectal atresia
  • Gastroschisis

Genitourinary

  • Renal agenesis
  • Hydronephosis
  • Cystic kidneys
  • Anal/rectal atresia

Skeletal

• Caudal regression syndrome

10.4.2.2 Maternal

Preconceptional maternal complications include nephropathy, neuropathy, retinopathy, hypertension, and diabetic ketoacidosis. Diabetic nephropathy is associated with other complications including preeclampsia, anemia, intrauterine growth restriction, fetal demise, and preterm delivery [28, 29]. If maternal glycemic levels are in optimal control before conception, the severity of complications and further renal deterioration during and after pregnancy are reduced. Pregnancy itself is not a risk factor for the development or progression of diabetic neuropathy. Gastroparesis, a condition in which the stomach's ability to empty its contents is impaired because of a possible disruption of nerve stimulation to the intestine, occurs more often in type 1 diabetes. Women with gastroparesis may experience nausea, vomiting abdominal discomfort and difficulty in controlling blood glucose. Few studies have been published on gastroparesis and pregnancy. One case report noted severe and intractable vomiting in two women with gastroparesis resulting in fetal demise in one of the pregnancies [30]. The effect of pregnancy on diabetic retinopathy depends on the severity of the condition, whether proteinuria or hypertension are present. In most cases, background retinopathy regresses after delivery. Proliferative retinopathy may progress if the condition was untreated prior to pregnancy [31, 32]. Laser photocoagulation is contraindicated in pregnancy, and the woman is advised to delay conception to avoid further eye damage. Obesity is a risk factor for hypertension and is primarily associated with type 2 diabetes [3, 34]. Diabetic ketoacidosis occurs more rapidly in pregnancy than in nonpregnancy because of increased insulin resistance and accelerated starvation ketosis. Factors that precipitate diabetic ketoacidosis include hyperemesis, gastroparesis, insulin pump failure, and certain medications, such as steroids [35].

Complications that develop during pregnancy include hypertensive disorders, polyhydramnios, preterm delivery, and cesarean section. Poor blood glucose control in early pregnancy is associated with the development of preeclampsia and pregnancy-induced hypertension [35]. Although the etiology of polyhydramnios (excessive amniotic fluid) is not well understood, it is associated with suboptimal blood glucose control. Macrosomia may warrant preterm or cesarean delivery.

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