Fetal pulse oximetry: correlation between oxygen desaturation, duration, and frequency and neonatal outcomes

The purpose of this study was to identify the threshold of fetal arterial oxyhemoglobin saturation that predicts neonatal acidosis and adverse outcomes.

Fetal oxygen saturation data from a published randomized controlled trial of fetal pulse oximetry were evaluated in relation to the number and duration of low fetal oxygen saturation episodes and neonatal outcomes. Fetal oxygen saturation episodes (epochs) of at least 10-second duration were categorized into the following groups: (1). <30% and >or=25%, (2). <25% and >or=20%, (3). <20%, and (control) randomly selected control subjects >30%.

One hundred seventy-four fetal heart rate tracings were identified. An analysis of mean umbilical artery pH revealed a significant difference between groups 1 and 3 compared with the control subjects. The incidence of adverse neonatal outcome was significantly greater when the number of epochs exceeded 10. An analysis of the duration of fetal oxygen saturation of <30%, as correlated with neonatal compromise, was not significant.

This study confirms previous findings that fetal oxygen saturation of <30% is associated with declining fetal arterial pH. There appears to be an association between adverse neonatal outcomes and >10 epochs of <30%.