IUGR is present when fetal growth stops and, over time, declines to less than the 5th percentile of growth for gestational age or when growth proceeds slowly, but absolute size remains less than the 5th percentile. Growth restriction may result from fetal conditions that reduce the innate growth potential, such as fetal rubella infection, primordial dwarfing syndromes, chromosomal abnormalities, and congenital malformation syndromes. Reduced fetal production of insulin and insulin-like growth factor I is associated with fetal growth restriction. Placental causes of IUGR include villitis (congenital infections), placental tumors, chronic abruptio placentae, twin-to-twin transfusion syndrome, and placental insufficiency. Maternal causes include severe peripheral vascular diseases that reduce uterine blood flow (chronic hypertension, diabetic vasculopathy, and preeclampsia/eclampsia), reduced nutritional intake, alcohol or drug abuse, cigarette smoking, and uterine constraint (noted predominantly in mothers of small stature with a low prepregnancy weight) and reduced weight gain during pregnancy. The outcome of IUGR depends on the cause of the reduced fetal growth and the associated complications after birth (Table 58-2). Fetuses subjected to chronic intrauterine hypoxia as a result of uteroplacental insufficiency are at an increased risk for the comorbidities of birth asphyxia, polycythemia, and hypoglycemia. Fetuses with reduced tissue mass due to chromosomal, metabolic, or multiple congenital anomaly syndromes have poor outcomes based on the prognosis for the particular syndrome. Fetuses born to small mothers and fetuses with poor nutritional intake usually show catch-up growth after birth.
Fetal size does not always correlate with functional or structural maturity. Determining fetal maturity is crucial when making a decision to deliver a fetus because of fetal or maternal disease. Fetal gestational age may be determined accurately on the basis of a correct estimate of the last menstrual period. Clinically relevant landmark dates can be used to determine gestational age; the first audible heart tones by fetoscope are detected at 18 to 20 weeks (12 to 14 weeks by Doppler methods), and quickening of fetal movements usually is perceived at 18 to 20 weeks. However, it is not always
Intrauterine fetal Placental insufficiency, hypoxia, acidosis, demise infection, lethal anomaly
Temperature Cold stress, ↓ fat stores, hypoxia, instability hypoglycemia
Perinatal asphyxia ↓ Uteroplacental perfusion during labor with or without chronic fetal hypoxia-acidosis, meconium aspiration syndrome
Hypoglycemia ↓ Tissue glycogen stores; ↓ gluconeogenesis, hyperinsulinism, ↑ glucose needs of hypoxia, hypothermia, relatively large brain
Polycythemia-Fetal hypoxia with ↑ erythropoietin production hyperviscosity
Reduced oxygen Hypoxia, hypoglycemia, starvation effect, poor consumption/ subcutaneous fat stores hypothermia
Dysmorphology Syndrome anomalads, chromosomal-genetic disorders, oligohydramnios-induced deformations
Pulmonary Hypothermia, polycythemia, hypoxia hemorrhage
Modified from Carlo WA: The high-risk infant. In Kliegman RM, Stanton BF, St.
Geme JW, et al, editors: Nelson Textbook of Pediatrics, ed 19, Philadelphia, 2011, Elsevier Science.
*Other problems are common to the gestational age–related risks of prematurity if born before 37 weeks.
possible to determine fetal maturity by such dating, especially in a high-risk situation, such as preterm labor or a diabetic pregnancy.