Relationship between fetal pulmonary trunk and ductus arteriosus flow velocity waveforms in early normal pregnancy

A tetralogy of fallot associated with a stenotic pulmonary valve and agenesis of the ductus arteriosus in a 13-week-old fetus: the role of postmortem examination

Prenatal diagnosis at very early gestational age may disclose fetal anomalies, although this diagnosis is limited by lack of details on ultrasound (US) examination; hence, the importance of postmortem (PM) examination. We present a case of a 13-week-old fetus terminated as a result of significantly raised nuchal translucency, which additionally presented a tetralogy of Fallot with a stenotic pulmonary valve and agenesis of ductus arteriosus. These cardiac defects are not detected by US at this gestational age. On the other hand, PM examinations are being performed more frequently in these cases with the aid of a dissecting microscope and using delicate instruments. This case illustrates the need for a closer collaboration between fetal medicine and fetal pathology in order to reach a more accurate diagnosis, which provides the basis for adequate reproductive counseling.

Fetal hemodynamics

Starting in the left cardiac ventricle the reader is taken on a guided tour on a fetal erythrocyte as measured by Doppler ultrasound. Up in the ascending aorta we move through the aortic isthmus to the descending aorta and the internal umbilical arteries, which fuse around the umbilical cord. With fresh oxygen from the placenta our erythrocyte moves in an accelerating continuous flow along the umbilical vein to the ductus venosus. After having reached the left ventricle again it now passes through a coronary artery to the right atrium and eventually the ductus arteriosus or the pulmonary circulation. Concepts of pulsatility, impedance and resistance are presente in the context of their clinical applicability in Doppler waveforms of various fetal vessels.

Blood flow velocity waveforms of the fetal pulmonary artery and the ductus arteriosus: reference ranges from 13 weeks to term

OBJECTIVE

To establish reference ranges for blood flow velocity waveforms of the fetal main pulmonary artery and the ductus arteriosus during the second and third trimesters of pregnancy.

METHODS

A prospective cross-sectional echocardiographic study was performed in 222 normal fetuses from 13 to 41 weeks of gestation using high resolution/color Doppler ultrasound equipment.

RESULTS

Gestational age-specific reference ranges are given for peak velocity across the pulmonary valve, velocities in the ductus arteriosus, peak systolic velocity in the ductus arteriosus-to-peak velocity across the pulmonary valve ratio, ductal systolic velocity-to-diastolic velocity ratio, ductal resistance index and ductal pulsatility index. In the ductus arteriosus, increasing fetal heart rate was significantly associated with increasing end-diastolic velocity and decreasing systolic-to-diastolic ratio, decreasing resistance index, and decreasing pulsatility index.

CONCLUSIONS

Based on a prospective study in more than 200 normal fetuses, the data provide gestational age specific reference ranges for blood flow velocity waveforms of the fetal pulmonary artery and the ductus arteriosus. The reference ranges may be helpful in prenatal diagnosis of cardiac malformations and ductal obstruction from 13 to 41 weeks of gestation.