Fetal oxygen saturation and uterine contractions during labor

Oxygen availability to the fetus during uterine contractions has not been widely reported. We examined whether fetal oxygen saturation (FSpO(2)) values and signal quality (SQ) were affected by uterine contractions. An intrauterine pressure catheter and a Nellcor FS14 fetal oxygen saturation sensor (Nellcor Puritan Bennett Inc., Pleasanton, CA) were placed transvaginally during the first stage of 17 labors. Fetal SpO(2) and SQ units were recorded on a beat-to-beat basis and 10 sec averages of the data calculated over 25 contractions per patient. Five epochs were determined: (1) 30 sec prior to a contraction; (2) during a contraction; (3)50 sec following completion of a contraction; (4) noncontraction periods, excluding epochs 1 or 3; and (5) equivocal, that is, overlap of epochs 1-3. Mean FSpO(2) was lowest during epoch 3 (45.0) and highest during epoch 2 (47.3%) (p < 0.001). This small difference is unlikely to be of any clinical significance, however. Mean signal quality was lowest in epoch 1 (42.8 units) and highest in epoch 4 (48.0 units) (p < 0.05), that is, in noncontraction periods. We conclude that FSpO(2) and SQ were unaffected by uterine contractions.