Variation by state in outcomes classification for deliveries less than 500 g in the United States

The purpose of this study is to explore state-level fetal death rates and <24 h infant mortality rates for deliveries less than 500 g in order to estimate outcomes classification differences at the edge of viability. We selected singleton deliveries to US resident mothers born <500 g and >20 weeks gestation from the NCHS live birth-infant death and fetal death files for 1999-2002 (n = 37,813). Infant deaths within 24 h of birth were selected to estimate odds of classification as a fetal death versus a live birth/infant death by state. Logistic regression was used to derive odds of classification as a fetal death and to adjust for maternal characteristics, calculating unadjusted and adjusted odds ratios. We identified 37,813 outcomes from 48 states reporting in this birthweight category. Unadjusted odds of classification of outcomes as a fetal death versus a live birth/death within 24 h by state ranged from OR = 0.38 (95% CI = 0.24-0.59) to OR = 2.93 (95% CI = 2.26-3.78); adjusted for maternal age and race, the range narrowed slightly to a OR = 0.31 (95% CI = 0.20-0.48) to aOR = 2.54 (95% CI = 1.96-3.30). Six states were more likely to classify outcomes as a live birth/infant death, while 14 states were more likely to classify as a fetal death, when compared to a large reference state. The remaining states did not differ significantly in their outcomes. The fraction of outcomes classified as fetal deaths varied by state during the years studied. This study suggests fetal death and early infant death outcomes reported for babies less than 500 g reflect differential classification thus influencing the validity of these vital statistics data at the state level. Further studies are needed to explore the factors that influence these differences.