The infant mortality rate encompasses the neonatal and the postneonatal periods. In the United States, it declined to 6.15:1000 in 2010. The rate for African American infants was approximately 11.6:1000. The most common causes of
Abruptio placentae Chromosomal anomalies Congenital malformations (heart, CNS, renal) Hydrops fetalis Intrauterine asphyxia* Intrauterine infection* Maternal underlying disease (chronic hypertension, autoimmune disease, diabetes mellitus) Multiple gestation* Placental insufficiency* Umbilical cord accident
CNS, Central nervous system. *Common.
perinatal and neonatal death are listed in Table 58-1. Overall, congenital anomalies and diseases of the premature infant are the most significant causes of neonatal mortality.
Low birth weight (LBW) infants, defined as infants having birth weights of less than 2500 g, represent a disproportionately large component of the neonatal and infant mortality rates. Although LBW infants make up only about 6% to 7% of all births, they account for more than 70% of neonatal deaths. IUGR is the most common cause of LBW in developing countries, whereas prematurity is the cause in developed countries.
Very low birth weight (VLBW) infants, weighing less than 1500 g at birth, represent about 1% of all births but account for 50% of neonatal deaths. Compared with infants weighing 2500 g or more, LBW infants are 40 times more likely to die in the neonatal period; VLBW infants have a 200-fold higher risk of neonatal death. The LBW rate has not improved in recent years and is one of the major reasons that the U.S. infant mortality rate is high compared with other large, modern, industrialized countries.
Maternal factors associated with a LBW caused by premature birth or IUGR include a previous LBW birth, low socioeconomic status, low level of maternal education, no antenatal care, maternal age younger than 16 years or older than 35 years, short interval between pregnancies, cigarette smoking, alcohol and illicit drug use, physical (excessive standing or walking) or psychological (poor social support) stresses, unmarried status, low pre-pregnancy weight (<45 kg), poor weight gain during pregnancy (<10 lb), and African American race. LBW and VLBW rates for African American women are twice the rates for white women. The neonatal and infant mortality rates are nearly twofold higher among African American infants. These racial differences are only partly explained by poverty.
Fetal size can be determined accurately by ultrasound techniques. Fetal growth can be assessed by determining the fundal height of the uterus through bimanual examination of the gravid abdomen. Ultrasound measurements of the fetal biparietal diameter, femur length, and abdominal circumference are used to estimate fetal growth. A combination of these measurements predicts fetal weight. Deviations from the normal fetal growth curve are associated with high-risk conditions.