Obstetric determinants of neonatal survival: Antenatal predictors of neonatal survival and morbidity in extremely low birth weight infants

OBJECTIVE: The aim of the study was to compare clinical and ultrasonographi c variables obtained before delivery as predictors of neonatal survival and morbidity in infants weighing less than or equal to 1000 g at birth. STUDY DESIGN: Maternal data available before the birth of singleton infants with birth weights less than or equal to 1000 g who were delivered at the 11 tertiary perinatal centers of the National institute of Child Health and Human Development Network of Maternal-Fetal Medicine Research Units were s tudied. Births that followed extramural delivery, antepartum stillbirths, m ultiple gestations, induced abortions, infants with major malformations, an d fetuses delivered at <20 weeks' gestation were excluded. Ultrasonographic variables, including estimated fetal weight, obstetrically estimated gesta tional age, femur length, and biparietal diameter, and clinical variables, such as maternal race, antenatal care, substance abuse, medical treatment, reason for delivery, fetal gender, and presentation, were studied with logi stic regression as predictors of neonatal outcome, including intrapartum st illbirth, neonatal death, and survival to 120 days after birth or to discha rge from the hospital with or without the presence of markers of major morb idity. RESULTS: Eight hundred eight infants met enrollment criteria; 63 were exclu ded because of incomplete data and 32 were excluded because of malformation s, leaving 713 for analysis, 386 of whom had an ultrasonographic examinatio n within 3 days of delivery that recorded femur length, biparietal diameter , and estimated fetal weight. Forty-two percent of births were the result o f preterm labor, 22% were the result of preterm ruptured membranes, 12% wer e the result of preeclampsia or eclampsia, 9% were the result of fetal dist ress, 4% were the result of placenta previa or abruptio placentae, and 2% w ere the result of intrauterine growth restriction. Perinatal mortality befo re 24 weeks' gestation exceeded 81% (19% stillbirths and 62% neonatal death s) but declined sharply thereafter. Most survivors born before 26 weeks' ge station had serious morbidity. Fetal femur length and estimated gestational age predicted survival better than did biparietal diameter or estimated fe tal weight. Infants who survived with markers of serious long-term morbidit y could not be distinguished from those who survived without morbidity mark ers before delivery by ultrasonography or clinical data. Threshold Values f or ultrasonographic measurements of biparietal diameter and femur length we re developed to distinguish fetuses with no chance of survival. CONCLUSION: Ultrasonographic assessment of either fetal femur length or ges tational age predicts neonatal mortality better than do other antenatal tes ts. No tests accurately predicted neonatal morbidity in infants weighing le ss than or equal to 1000 g at birth.