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.