Infant mortality rates are higher for pregnancies in which prenatal
care is initiated after the first trimester of pregnancy and in
infants born to teenagers or to women 40 years of age or older who
did not complete high school, were unmarried, or smoked during pregnancy.
Infant mortality is also higher for male infants, multiple births,
and infants born preterm or at low birth weight. In many instances,
the precipitating cause of preterm delivery remains undetected, but
risk factors for premature birth include uterine abnormalities,
placental bleeding including abruptio placenta associated with cocaine
use, maternal chronic illnesses, multifetal gestation, premature
rupture of the membranes, chorioamnionitis, and bacterial vaginosis.
Bacterial vaginosis, a short cervix, and the presence of fetal fibronectin
in the vaginal tract are predictors of preterm delivery, but treatment
of the bacterial vaginosis has been ineffective in preventing prematurity.
Premature delivery complicates over 10% of births but contributes
disproportionately to at least two thirds of the infant deaths and
to a significant amount of neonatal and long-term morbidity, which
may include cerebral palsy, mental restriction, physical handicap,
blindness, and deafness in addition to major and minor school adaptive
and learning problems.14-16 Although there has
been a substantial decline in the number of medically preventable
deaths and deaths from respiratory distress syndrome, the number
of deaths from extremely low birth weight has increased relative
to other causes; asphyxia, birth trauma, early-onset sepsis, and
meconium aspiration syndrome have been reduced to a minimum. Nonetheless,
congenital malformation is the leading cause of infant death in
the United States and accounts for a much greater proportion of
infant mortality than does premature birth. To further reduce neonatal
mortality, the incidence of lethal congenital malformations and
very-low-birth-weight infants must be addressed; congenital anomalies
cause approximately 23% of infant mortality, and short gestation
and low birth weight, about 15%.