Etiology of low-birthweight birth: a population-based study

Preterm and low-birthweight births remain the major correlates of infant mortality in the United States. The recognition that these births result from varying proximal etiologies is essential to the development of preventive strategies specific to each etiologic group.

Using vital statistics data tapes provided by the North Carolina Center for Health and Environmental Statistics, mothers in 20 counties who delivered infants with birthweights between 1 pound and 5 pounds, 8 ounces were identified. Maternal hospital records of 4,754 women were reviewed for data about prenatal and intrapartal events. Two perinatologists classified births into four proximal etiology groups: term-lowbirthweight, medically indicated preterm birth, preterm premature rupture of membranes, and idiopathic preterm birth. Information from birth certificate and hospital records was merged to provide an expanded data set.

Race, age, education, and marital status are associated with different patterns of proximal etiology. Rates were higher for all etiologies in black women and in young women; however, the absolute number of LBW births was highest among white women. Idiopathic preterm birth was highest in black women and decreased as age increased; medical indications for preterm birth increased with increasing age.

Classification of LBW births by etiologic group provides insights of value to both clinicians and researchers. Studies in which LBW and/or preterm birth are the outcome variables will be enhanced by identifying etiology. Multiple preventive strategies should address varying etiologic groups.