Effect of labor on maternal cerebral blood flow velocity

OBJECTIVE: Our purpose was to determine the effect of contractions and second-stage pushing on cerebral blood flow velocity as an indirect assessment of cerebral hemodynamic changes during labor and delivery. STUDY DESIGN: A prospective cohort of 15 normotensive patients in early labor had maternal middle cerebral blood flow velocity assessed continuously with transcranial Doppler ultrasonography. Assessment was performed during the peak of a contraction, during the trough of a contraction, and with pushing in the second stage. We assessed systolic, diastolic, mean cerebral blood flow velocity (in centimeters per second), and pulsatility index over four contractions. We used analysis of variance to compare velocities at these three stages. RESULTS: Mean maternal cerebral blood flow velocity fell significantly (61.2 +/- 6.4, 50 +/- 10.2, 52.2 +/- 6.5 cm/sec) (p < 0.008). Pulse rate rose significantly by 16 beats/min (p < 0.0001), but no significant change in blood pressure occurred in patients during second-stage labor when pushing. CONCLUSIONS: Middle cerebral vessels vasodilated during the peak of contractions and second-stage pushing as assessed by transcranial Doppler ultrasonography. Pushing in the second stage with the Valsalva maneuver does not expose the patient to a greater risk for middle cerebral vasospasm than contractions developing in the first stage.