Gestational age Gestational Age Gestational age and growth parameters help identify the risk of neonatal pathology. Gestational age is the primary determinant of organ maturity. Gestational age is usually defined as the number... read more 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.
The Fenton growth charts provide a more precise assessment of growth vs gestational age ( see Figure: Fenton growth chart for preterm boys Fenton growth chart for preterm boys and see Figure: Fenton growth chart for preterm girls Fenton growth chart for preterm girls ).
Etiology of LGA infant
Other than genetically determined size, maternal diabetes mellitus Diabetes Mellitus in Pregnancy Pregnancy makes glycemic control more difficult in preexisting type 1 (insulin-dependent) and type 2 (non–insulin-dependent) diabetes but does not appear to exacerbate diabetic retinopathy,... read more 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.
Symptoms, Signs, and Treatment
LGA infants are large, obese, and plethoric. The 5-minute Apgar score Apgar score Extensive physiologic changes accompany the birth process, sometimes unmasking conditions that posed no problem during intrauterine life. For that reason, a person with neonatal resuscitation... read more 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 Birth Injuries The forces of labor and delivery occasionally cause physical injury to the infant. The incidence of neonatal injury resulting from difficult or traumatic deliveries is decreasing due to increasing... read more , particularly including
Other complications occur when weight is > 4000 g. There is a proportional increase in morbidity and mortality due to the following:
Respiratory distress Respiratory Distress Syndrome in Neonates Respiratory distress syndrome is caused by pulmonary surfactant deficiency in the lungs of neonates, most commonly in those born at < 37 weeks gestation. Risk increases with degree of prematurity... read more (and need for ventilatory assistance)
Infants of diabetic mothers (IDMs)
IDMs are at risk of
Hypocalcemia Neonatal Hypocalcemia Hypocalcemia is a total serum calcium concentration < 8 mg/dL (< 2 mmol/L) in term infants or < 7 mg/dL (< 1.75 mmol/L) in preterm infants. It is also defined as an ionized calcium... read more and hypomagnesemia Hypomagnesemia Hypomagnesemia is serum magnesium concentration < 1.8 mg/dL (< 0.70 mmol/L). Causes include inadequate magnesium intake and absorption or increased excretion due to hypercalcemia or medications... read more
Certain congenital anomalies
Hypoglycemia Neonatal Hypoglycemia Hypoglycemia is difficult to define in neonates but is generally considered a serum glucose concentration < 40 mg/dL (< 2.2 mmol/L) in symptomatic term neonates, < 45 mg/dL (< 2... read more 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 Neonatal Hypocalcemia Hypocalcemia is a total serum calcium concentration < 8 mg/dL (< 2 mmol/L) in term infants or < 7 mg/dL (< 1.75 mmol/L) in preterm infants. It is also defined as an ionized calcium... read more and hypomagnesemia Hypomagnesemia Hypomagnesemia is serum magnesium concentration < 1.8 mg/dL (< 0.70 mmol/L). Causes include inadequate magnesium intake and absorption or increased excretion due to hypercalcemia or medications... read more 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 Perinatal Polycythemia and Hyperviscosity Syndrome Polycythemia is an abnormal increase in red blood cell mass, defined in neonates as a venous hematocrit ≥ 65%; this increase can lead to hyperviscosity with sludging of blood within vessels... read more 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 Neonatal Hyperbilirubinemia Jaundice is a yellow discoloration of the skin and eyes caused by hyperbilirubinemia (elevated serum bilirubin concentration). The serum bilirubin level required to cause jaundice varies with... read more 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 Respiratory Distress Syndrome in Neonates Respiratory distress syndrome is caused by pulmonary surfactant deficiency in the lungs of neonates, most commonly in those born at < 37 weeks gestation. Risk increases with degree of prematurity... read more (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 Infants of diabetic mothers (IDMs) is discussed elsewhere.
Congenital anomalies are more likely in IDMs because maternal hyperglycemia at the time of organogenesis is detrimental. Specific anomalies include
Congenital heart disease Overview of Congenital Cardiovascular Anomalies Congenital heart disease is the most common congenital anomaly, occurring in almost 1% of live births ( 1). Among birth defects, congenital heart disease is the leading cause of infant mortality... read more (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.
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