The impact of labor at term on measures of neonatal outcome.

Objective: The purpose of this study was to determine risk assessments for a spectrum of neonatal outcomes with elective cesarean delivery versus a trial of labor for previous cesarean section and otherwise healthy patients who deliver at term.

Study Design: The perinatal/neonatal database of St. Joseph's Health Care, London, Ontario, Canada, was used to obtain the umbilical cord pH and base excess values, incidence of adverse neonatal outcomes, and patient demographics for all term (> or =37 weeks of gestation), singleton, liveborn, or intrapartum demise infants with no major anomalies who were delivered between January 1992 and March 2002 (n = 33,709 infants). Patient groupings (all patient, patient with previous cesarean delivery, and low-risk patient) with no labor versus labor were studied by a comparison of mean values/incidences for those neonatal outcomes that were available from the database with the use of linear and logistic regression analysis and controlling for potentially confounding variables.

Results: Labor was associated with a small drop in umbilical artery pH from approximately 7.27 to 7.25 and base excess from approximately -3.1 to -5.4 mmol/L, but this was generally well tolerated, with no difference in the incidence of 5-minute Apgar scores of <7 for any of the patient population groupings. Neonatal respiratory morbidity was increased generally in the group of elective cesarean delivery patients, which resulted in increased neonatal intensive care unit triage/admission even out to 7 days; some of this risk was likely to persist even with a policy of elective cesarean delivery after 39 weeks of gestation. Although we found no significant difference in the incidence of pathologic acidemia at birth with an umbilical artery pH <7.00, there was a risk for intrapartum/neonatal death that could be attributed to labor events per se that ranged from 1 of 882 for the patients with previous cesarean delivery to 1 of 3406 for the low-risk patients.

Conclusion: For otherwise healthy patients at term, the risk of adverse neonatal outcomes is low, with the choice between elective cesarean delivery and trial of labor in general balancing the low risk of increased respiratory morbidity and thereby neonatal intensive care unit triage/admission against the extremely low risk of labor-related infant death and severe morbidity. However, this balance for the patients with previous cesarean delivery appears shifted, with less benefit from a trial of labor in terms of reduced respiratory morbidity and neonatal intensive care unit triage/admission and with increased labor-related severe morbidity/death, albeit with all of these still at a low level.