Doppler sonography of normal fetal vertebral and internal carotid arteries during pregnancy.

Abstract

The aim of this study was to determine the resistance index (RI) in the fetus in both the vertebral artery and the internal carotid artery and to evaluate the relationship of those RIs with that of the umbilical artery. In this prospective study, color Doppler examinations of the vertebral, internal carotid, and umbilical arteries were performed in fetuses with normal growth between 17 and 41 weeks' gestational age. For every week, the 10th, 50th, and 90th percentiles of the RIs in the 3 arteries plus the ratios of the RIs of the vertebral and umbilical arteries and of the internal carotid and umbilical arteries were calculated. In 225 examinations in 114 women, the vertebral and internal carotid arteries showed similar RI patterns, with higher RIs at mid gestation. The only difference was that the RIs in the internal carotid artery reached maximum values at a slightly later gestational age (26-28 weeks) than did those in the vertebral artery (24-25 weeks). Also, the RIs in the vertebral artery were slightly higher than were those in the internal carotid artery. RI values in the umbilical artery decreased progressively throughout gestation. Conversely, the ratios of the RIs in the vertebral and umbilical arteries and those of the RIs in the internal carotid and umbilical arteries increased slightly until the end of pregnancy, with the former ratios always higher than the latter ones. In normal fetuses, the pattern of blood flow resistance in the vertebral artery resembles that in the internal carotid artery. However, compared with the internal carotid artery, the vertebral artery shows higher absolute RIs with maximum values appearing earlier in the course of pregnancy.