The effect of uterine contractions on fetal oxygen saturation

OBJECTIVE: To find out what happens to fetal arteriolar oxygen saturation during a uterine contraction. DESIGN: Prospective observational study. SETTING: Labour ward, St James's University Hospital, Leeds. SUBJECTS: Eighteen women in normal labour monitored with a fetal scalp surface pulse oximetry sensor, an intrauterine pressure catheter, and a head to cervix force transducer. METHODS: The effect of intrauterine pressure and head to cervix force on fetal arteriolar oxygen saturation was examined using time series analysis and a regression model of 159 contractions. OUTCOME MEASURE: Fetal oxygen saturation during a contraction. RESULTS: The average oxygen saturation drops after a contraction. The greatest drop in oxygen saturation is reached 92 s after the peak of a contraction and takes approximately 1 min 30 s to recover (P = 0.036). CONCLUSION: Uterine contractions during normal labour affect fetal oxygen saturation.