Placental abnormalities: Placental causes include any factor that compromises the uteroplacental blood supply. Examples include placenta previa (low implantation of the placenta), placental abruption (separation of placenta from the decidua by a retroplacental clot), or placental infarction. With placental (and maternal) abnormalities, the fetal growth restriction is asymmetric http://ebooksmedicine.net (i.e., the brain is spared relative to visceral organs such as the liver).
• Maternal factors: This category comprises by far the most common causes of the growth deficit in SGA infants. Important examples are vascular diseases such as preeclampsia (“toxemia of pregnancy”) (Chapter 19) and chronic hypertension. Another class of maternal diseases increasingly being recognized in the setting of fetal growth restriction is acquired or inherited diseases of hypercoagulability (i.e., thrombophilias) (Chapter 4). The list of other maternal conditions associated with fetal growth restriction is long, but some of the avoidable influences are maternal narcotic abuse, alcohol intake, and heavy cigarette smoking (as noted previously, many of these same causes also are involved in the pathogenesis of congenital anomalies). Drugs causing fetal growth restriction in similar fashion include teratogens, such as the commonly administered anti-convulsant phenytoin (Dilantin), as well as nonteratogenic agents. Maternal malnutrition (in particular, prolonged hypoglycemia) also may affect fetal growth.
Not only is the growth-restricted infant handicapped in the perinatal period, but the deficits persist into childhood and adult life. Affected persons are thus more likely to have cerebral dysfunction, learning disabilities, and sensory (i.e., visual and hearing) impairment.
The most common cause of respiratory distress in the newborn is respiratory distress syndrome (RDS), also know as hyaline membrane disease because of the formation of “membranes” in the peripheral air spaces observed in infants who succumb to this condition. An estimated 24,000 cases of RDS are reported annually in the United States. Improvements in management of this condition have sharply decreased deaths due to respiratory insufficiency from as many as 5000 per year a decade ago to fewer than 900 cases yearly. It is primarily a disorder of premature infants. Less common causes include excessive sedation of the mother, fetal head injury during delivery, aspiration of blood or amniotic fluid, and intrauterine hypoxia secondary to compression from coiling of the umbilical cord about the neck.
RDS occurs in about 60% of infants born at less than 28 weeks’ gestation, 30% of those born between 28 to 34 weeks’ gestation, and less than 5% of those born after 34 weeks’ gestation. There are also strong though not invariable associations with male gender, maternal diabetes, and delivery by cesarean section.