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Prospective study establishes blood flow reference ranges in low-risk pregnancies, suggesting important fetal health indicators.
OBJECTIVE: To establish longitudinal reference ranges for the umbilical vein (UV) diameter, velocities and volume blood flow (Q(uv)) at a free loop of the umbilical cord and estimate the UV spatial velocity profile at this site. METHODS: This was a prospective study of 53 low-risk pregnancies. The UV diameter and blood flow velocities were measured at 4-weekly intervals from 22 + 0 to 39 + 6 weeks of gestation (232 observations) using B-mode ultrasonography and pulsed-wave Doppler. Multilevel regression modeling was used to estimate the reference percentiles. RESULTS: The mean UV diameter, velocities and Q(uv) increased with advancing gestation, whereas the Q(uv) normalized for estimated fetal weight decreased. The UV spatial velocity profile coefficient was 0.62. CONCLUSION: We have established reference ranges for serial measurements of Q(uv) at a free loop of the umbilical cord during the second half of pregnancy. The spatial velocity profile of the UV is not completely parabolic at this site.
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Flo et al. (2010) studied this question.
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