BMC Public Health 2005, 5:79 http://www.biomedcentral.com/1471-2458/5/79 year 2000, over 1,500 excess infant deaths occurred among adolescent mothers. The etiology explaining the higher mortality risk for ado- lescent mothers has been debated for as long as the phe- nomenon has been observed. Miller argued that socioeconomic status has a direct effect on infant mortal- ity, confounding the role of young maternal age, in a study of 2,019 U.S. counties from 1971–1975 [4]. Many studies point towards low birth weight (including infants born preterm and those small-for-gestational age) as the predominant proximate marker of infant mortality [5- 10]. Fraser, in a large study spanning 20 years of live births from Utah, found maternal age to be an independent pre- dictor for poor birth outcomes, but this study did not spe- cifically address infant mortality or socioeconomic status directly [11]. The defining influence of the biology of ado- lescent pregnancy, risky adolescent behavior, nutrition, race, socioeconomics, and adequacy of prenatal care – or the interaction among these variables – remains contro- versial. Certainly poverty, minority status, suboptimal prenatal care, poor education and unmarried status are more common in teenage compared to older mothers, and are known risk factors for low birth weight, preterm birth and higher infant mortality in the United States [11]. Adolescent mothers are disproportionately poor. For example, in Missouri for 1997–1999, 79% of births to women aged 14–19 were covered by Medicaid compared to only 35.7% of births to women 20 and older [12]. Among adolescents living in poor communities, 69% report having had intercourse, compared to 37% of those living in more affluent neighborhoods [13]. Support can be found to defend or refute all or none of these factors as independent risk factors [6,7,11,14-16]. We examined linked birth-death certificate data for Mis- souri residents to assess the role of poverty status and other potential risk factors on infant mortality among teenage mothers. We hypothesized that teen motherhood is highly confounded by poverty, and that there is no independent effect of adolescent age on infant mortality. Our analysis distinguished neonatal and post-neonatal mortality among younger and older adolescent mothers. Methods Study design This was a population-based cohort study using Mis- souri's linked birth-death certificate files for 1997–1999. This period was chosen since it provided a sufficiently large study population with the most current birth-related data. To test the primary hypothesis, we compared infant mortality rates of adolescent and older mothers while controlling for socioeconomic status (defined by partici- pation in poverty assistance programs) and other known and purported risk factors. Cohort description The study population included all singleton live births for mothers who were Missouri residents and less than 20 years of age during 1997–1999. The study population was stratified by maternal age to identify younger (12–17 years) and older (18–19 years) adolescent mothers. A comparison population included a random sample of sin- gleton live births for mothers who were 20–34 years old during 1997–1999, since the infant mortality rates were relatively stable for this age group but higher for older mothers. Women other than non-Hispanic white or Afri- can American were excluded, because they comprised less than 3% of all live births in Missouri during the study period. Covariates The following covariates were extracted from the birth cer- tificate: race/ethnicity (non-Hispanic black or non-His- panic white), maternal education level (recorded as age appropriate based on the number of years of formal edu- cation completed by the mother), parity, marital status, tobacco or alcohol use (as dichotomous and categorical covariates based on the number of cigarettes per day or drinks per week), maternal weight gained during preg- nancy, adequacy of prenatal care utilization (based on the Kotelchuck index)[17], and socioeconomic status. The poorest women were defined as those receiving food stamps, since this program includes only those with per- sonal incomes less than 130% of the federal poverty level. Poor women were those defined as receiving Medicaid or WIC. In Missouri, pregnant women at or below 185% of the federal poverty level are eligible for Medicaid and WIC. While personal incomes can be used to identify women participating in poverty programs, we cannot assume that all non-participants are above 185% of the federal poverty level. All other women included those who did not participate in any of the three poverty assist- ance programs. Other covariates were clinical estimate of gestational age (20–28, 29–32, 33–36, ≥37 weeks) and birth weight (<2500, ≥ 2500 grams). Infant mortality included deaths that occurred during the neonatal (0–27 days) and post-neonatal (28–364 days) period. The underlying causes of death were divided into five catego- ries: 1) accidental, 2) respiratory arrest or sudden infant death syndrome, 3) infectious, 4) perinatal or congenital, 5) other deaths. Analysis Chi-square tests and student's unpaired t-tests were used to determine if categorical and continuous covariates, respectively, were significantly different for younger ver- sus older mothers. Overall infant mortality, as well as neo- natal mortality and post-neonatal mortality, was assessed as a function of the three age cohorts and stratified by race. Logistic regression was used to assess how each covariate Page 2 of 7 (page number not for citation purposes)