Birth weight threshold for postponing preterm birth.
OBJECTIVE: The study was designed to determine the birth weight threshold at which obstetric efforts intended to delay delivery might potentially improve rates of neonatal morbidity and mortality among pregnancies delivered after spontaneous preterm labor or rupture of the membranes. STUDY DESIGN: We studied 1147 singleton infants with birth weights between 1000 and 2499 gm and whose only complication was spontaneous preterm labor or preterm rupture of the membranes. The Mantel-Haenszel chi 2 statistic was used to evaluate trends for neonatal mortality and several indexes of morbidity. RESULTS: The birth weight threshold for neonatal mortality was 1600 gm (p < 0.001). For neonatal morbidity the threshold was between 1600 and 1900 gm (p < 0.008). CONCLUSION: Aggressive obstetric attempts to prevent preterm birth for infants whose weights exceed 1900 gm offers few apparent potential benefits.