Gestational age is loosely defined as the number of weeks between the first day of the mother's last normal menstrual period and the day of delivery. More accurately, the gestational age is the difference between 14 days before the date of conception and the date of delivery. Gestational age is not the actual embryologic age of the fetus, but it is the universal standard among obstetricians and neonatologists for discussing fetal maturation.
Other than genetically determined size, maternal diabetes mellitus is the major cause of large-for-gestational-age (LGA) infants. The large size results from the anabolic effects of high fetal insulin levels produced in response to excessive maternal blood glucose during gestation and sometimes increased caloric intake by the mother to compensate for glucose lost in urine. The less well controlled the mother’s diabetes during pregnancy, the larger is the size of the fetus.
Rare causes of macrosomia are Beckwith-Wiedemann syndrome (characterized by macrosomia, omphalocele, macroglossia, and hypoglycemia) and Sotos, Marshall, and Weaver syndromes.
LGA infants are large, obese, and plethoric. The 5-minute Apgar score may be low. These infants may be listless and limp and feed poorly. Delivery complications can occur in any LGA infant. Congenital anomalies and some metabolic and cardiac complications are specific to LGA infants of diabetic mothers.
Because of the infant’s large size, vaginal delivery may be difficult and occasionally results in birth injury, particularly including
Other complications occur when weight is > 4000 g. There is a proportional increase in morbidity and mortality due to the following:
IDMs are at risk of
Hypoglycemia is very likely in the first few hours after delivery because of the state of hyperinsulinism and the sudden termination of maternal glucose when the umbilical cord is cut. Neonatal hypoglycemia can be decreased by close prenatal control of the mother’s diabetes and early frequent feedings. Blood glucose levels should be closely monitored by bedside testing from birth through the first 24 hours. Oral treatment with 40% glucose gel may be tried first, but if there is persistent hypoglycemia, parenteral IV glucose is given.
Hypocalcemia and hypomagnesemia may occur but are usually transient and asymptomatic. Good prenatal glycemic control decreases the risk of neonatal hypocalcemia. Hypocalcemia typically does not require treatment unless there are clinical signs of hypocalcemia or total serum calcium levels < 7 mg/dL (< 1.75 mmol/L) or ionized calcium levels < 4 mg/dL (< 1 mmol/L) in term infants. Treatment should be based on ionized calcium levels because these levels more accurately reflect available calcium. Treatment is usually given with IV supplementation of calcium gluconate. Hypomagnesemia can interfere with the secretion of parathyroid hormone, so hypocalcemia may not respond to treatment until the magnesium level is corrected.
Polycythemia is slightly more common among infants of diabetic mothers. Elevated insulin levels increase fetal metabolism and thus oxygen consumption. If the placenta is unable to meet the increased oxygen demand, fetal hypoxemia occurs, triggering an increase in erythropoietin and thus hematocrit.
Hyperbilirubinemia occurs for several reasons. IDMs often have decreased tolerance for oral feedings (particularly when they are preterm) in the earliest days of life, which increases the enterohepatic circulation of bilirubin. Also, if polycythemia is present, the bilirubin load increases.
Respiratory distress syndrome (RDS) may occur because elevated insulin levels decrease surfactant production; pulmonary maturation may thus be delayed until late in gestation. RDS may develop even if the infant is delivered late preterm or term. Treatment of respiratory distress syndrome is discussed elsewhere.
Transient tachypnea of the newborn is 2 to 3 times more likely in IDMs because of the delay in fetal lung fluid clearance.
Congenital anomalies are more likely in IDMs because maternal hyperglycemia at the time of organogenesis is detrimental. Specific anomalies include
Congenital heart disease (hypertrophic cardiomyopathy, ventricular septal defect, transposition of the great arteries, and aortic stenosis)
Caudal regression syndrome
Small left colon syndrome
Persistently elevated insulin levels can also lead to increased deposition of glycogen and fat into cardiomyocytes. This deposition can cause transient hypertrophic cardiomyopathy, predominantly of the septum.
Maternal diabetes mellitus is the major cause of large-for-gestational-age infants.
Large size itself increases risk of birth injury (eg, clavicle or extremity long bone fracture) and perinatal asphyxia.
Infants of diabetic mothers also may have metabolic complications immediately after delivery, including hypoglycemia, hypocalcemia, and polycythemia.
Infants of diabetic mothers are also at risk of respiratory distress syndrome and congenital anomalies.
Good control of maternal glucose levels minimizes risk of complications.