Doppler study of the fetal cardiac function in prolonged pregnancies.

OBJECTIVE

To evaluate the association between fetal cardiac function and amniotic fluid index (AFI) in postterm fetuses, and to determine if changes in fetal cardiac function precede the occurrence of nonreassuring intrapartum fetal heart rate (FHR) patterns.

METHODS

Forty-five otherwise low-risk pregnant women between 41 and 43 weeks' gestation were studied longitudinally. Gestational age was confirmed in all patients by ultrasound before 20 weeks' gestation. Each subject had two or three tests performed every 3-4 days, including a non-stress test, a biophysical profile, and Doppler studies of the aortic and pulmonic outflow tracts. Aortic and pulmonic artery flow velocity waveforms were recorded slightly distal to the valves. Peak velocity, velocity time integral, and heart rate were calculated from the flow velocity waveforms we obtained. The change in AFI and aortic and pulmonic peak velocity and [velocity time integral] x [heart rate] were calculated for each fetus.

RESULTS

Labor was induced at 42 weeks' gestation in 20 patients, and 17 entered labor spontaneously. Changes in AFI, observed during the follow-up period, correlated significantly with changes in aortic peak velocity (r = 0.54, P < .01) and with aortic outflow [velocity time integral] x [heart rate] (r = 0.60, P < .001) but not with pulmonic peak velocity and [velocity time integral] x [heart rate]. The decrease in aortic peak velocity and aortic and pulmonic [velocity time integral] x [heart rate] was significantly higher (P < .01) in eight fetuses that developed a nonreassuring intrapartum FHR (reduced FHR variability, late decelerations, and severe variable decelerations) than in those who had an uneventful labor.

CONCLUSION

In prolonged pregnancies, cardiac function deteriorates in fetuses that develop a nonreassuring intrapartum FHR, and the changes in the left cardiac function correlate with changes in AFI.