Objective: To analyze labor outcomes in relation to masked fetal arterial oxyhemoglobin saturation values above or below 30%.
Methods: Consenting gravidas with uncomplicated pregnancies at or beyond 36 weeks' gestation underwent continuous fetal pulse oximetry. Pregnancy outcomes were compared between two groups: women with fetuses with at least one epoch of arterial oxyhemoglobin saturation below 30% (10 seconds or longer) and women with fetuses without such an episode. We also attempted to ascertain whether duration of saturation below 30% correlated with fetal compromise.
Results: We measured arterial oxyhemoglobin saturation in 129 fetuses, 69 (53%) of whom had at least one epoch of saturation below 30%. There were no statistically significant differences in labor and delivery outcomes between the high-saturation and low-saturation groups (eg, cesarean delivery: 13 versus 9%, P = .41; umbilical artery [UA] pH less than 7.20: 10 versus 9%, P > .999). However, as duration of fetal arterial oxyhemoglobin saturation below 30% increased from 10 seconds to longer than 9 consecutive minutes, the incidence of fetal compromise (considered present when at least one of the following criteria was met: cesarean delivery for nonreassuring fetal heart rate pattern, UA pH less than 7.20, admission to the special care nursery, or 5-minute Apgar score not more than 3) increased significantly (P = .002). The threshold duration of fetal arterial oxyhemoglobin saturation below 30% associated with increased fetal compromise was 2 minutes.
Conclusion: Transient fetal arterial oxyhemoglobin saturation values below 30% are common during normal labor and did not predict fetal compromise. Fetal arterial oxyhemoglobin saturation values less than 30% for 2 minutes or longer might be associated with fetal compromise.