Fetal vertebral artery Doppler reference values at 19-41 weeks of gestation.

OBJECTIVES

To establish Doppler reference values for the fetal vertebral artery resistance index (VA RI), pulsatility index (VA PI) and peak systolic velocity (VA PSV), and describe their normal ratios to the umbilical artery (UA) throughout the second and third trimester of pregnancy.

METHODS

Between 19 and 41 weeks of gestation, 484 ultrasound examinations of the fetal VA and UA were performed on singleton pregnant women with uncomplicated pregnancies. The VA was examined at the anatomical point where the artery surrounds the lateral masses of the atlas between the first cervical vertebra and the occipital bone, and values were obtained for the VA RI, VA PI and VA PSV. The 10th, 50th and 90th percentiles were subsequently generated for these parameters and their ratios to the UA.

RESULTS

The VA RI and VA PI reached their maximum values at the end of the second trimester. Both indexes subsequently decreased due to an increase in the diastolic flow. Conversely, the VA PSV values increased progressively until the end of gestation. As for the VA/UA ratios, the RI and PI were higher in the middle of the third trimester and decreased slightly afterwards. On the other hand, the PSV increased progressively until the end of pregnancy.

CONCLUSIONS

The fetal VA can be visualized with Doppler ultrasound as early as 19 weeks' gestation. In this study, reference values of the VA RI, PI and PSV and their ratios to the UA during the second half of pregnancy have been provided for fetal research. However, future work is necessary to further explore the possible applications of VA Doppler examination in fetal medicine.