Fetal cardiac time intervals determined by Doppler echocardiography.

One-hundred and eleven Doppler echocardiographic examinations were performed on 88 normal fetuses, ranging from 16 to 41 weeks of gestation. Aortic and pulmonary maximal velocity (MV), acceleration time (AT), ejection time (ET), MV/AT (acceleration velocity: AV) and AT/ET ratio in systole were assessed on each blood flow velocity waveform. Aortic MV and pulmonary MV correlated well with gestational age, respectively. Good correlations between aortic AT, pulmonary AT and gestational age were evident. There were correlations between aortic AT/ET ratio, pulmonary AT/ET ratio and gestational age, respectively. However, there was no correlation between aortic AV, aortic ET, pulmonary AV, pulmonary ET and gestational age, respectively. These findings may relate to alterations in pulmonary and placental vascular resistance with advance in gestation.