Risk factors for severe neonatal acidosis.

OBJECTIVE: Neonatal asphyxia may have severe consequences in term newborns. Our purpose was to identify possible risk factors of severe acidosis during pregnancy and labor.
METHODS: In a case-control study from January 2003 to December 2008 in three university perinatal centers (two French and one Canadian hospitals), we analyzed 226 women with term pregnancies complicated by severe neonatal acidosis (umbilical artery pH less than 7.00). Cases were individually matched with controls with a normal acid-base status (pH 7.15 or greater) paired by parity. Groups were compared for differences in maternal, obstetric, and fetal characteristics. Univariable and logistic conditional regression were used to identify possible risk factors.
RESULTS: Among 46,722 births after 22 weeks, 6,572 preterm births and 829 stillbirths or terminations of pregnancy were excluded. From the 39,321 live term births, 5.30% of pH values were unavailable. Severe acidosis complicated 0.63% of 37,235 term structurally normal pregnancies. By using multivariate conditional regression, maternal age 35 years or older (35.0% compared with 15.5%; odds ratio [OR] 5.58, 95% confidence interval [CI] 2.51-12.40), prior neonatal death (3.5% compared with 0%), prior cesarean delivery (24.7% compared with 6.6%; OR 4.08, 95% CI 1.71-9.72) even after excluding cases of uterine rupture, general anesthesia (8.4 compared with 0.9%; OR 8.04, 95% CI 1.26-50.60), thick meconium (6.4% compared with 2.8%; OR 5.81, 95% CI 1.72-19.66), uterine rupture (4.4% compared with 0%), and abnormal fetal heart rate (66.1% compared with 19.8%; OR 8.77, 95% CI 3.72-20.78) were independent risk factors of severe neonatal acidosis.
CONCLUSION: Prior cesarean delivery, maternal age 35 years or older, prior neonatal death, general anesthesia, thick meconium, uterine rupture, and abnormal fetal heart rate are independent risk factors of severe neonatal acidosis. LEVEL OF EVIDENCE: II.