Umbilical Vein Blood Flow in Uncomplicated Pregnancies: Systematic Review of Available Reference Charts and Comparison with a New Cohort

Abstract

The objectives of the study were (1) to perform a systematic review of the available umbilical vein blood flow volume (UV-Q) reference ranges in uncomplicated pregnancies; and (2) to compare the findings of the systematic review with UV-Q values obtained from a local cohort. Available literature in the English language on this topic was identified following the PRISMA guidelines. Selected original articles were further grouped based on the UV sampling sites and the formulae used to compute UV-Q. The 50th percentiles, the means, or the best-fitting curves were derived from the formulae or the reported tables presented by authors. A prospective observational study of uncomplicated singleton pregnancies from 20⁺⁰ to 40⁺⁶ weeks of gestation was conducted to compare UV-Q with the results of this systematic review. Fifteen sets of data (fourteen sets belonging to manuscripts identified by the research strategy and one obtained from our cohort) were compared. Overall, there was a substantial heterogeneity among the reported UV-Q central values, although when using the same sampling methodology and formulae, the values overlap. Our data suggest that when adhering to the same methodology, the UV-Q assessment is accurate and reproducible, thus encouraging further investigation on the possible clinical applications of this measurement in clinical practice.

Keywords: Doppler ultrasound; fetus; nutrition; oxygenation; reference ranges; reproducibility; umbilical cord; umbilical vein blood flow volume.

Figure 1

PRISMA flow diagram of the study selection. * Not identified through Pubmed or Scopus search strategy but cited in other articles similar to this systematic review or found by evaluating the bibliography of studies obtained from the research strategy. In red, the articles not found through the search strategy; in green, the articles selected for this systematic review.

Figure 2

The figure represents the percentiles for (a) umbilical vein blood flow volume (UV-Q); (b) UV-Q normalized for estimated fetal weight (UV-Q/EFW); and (c) UV-Q normalized for abdominal circumference (UV-Q/AC).

Figure 3

The figure represents (a) absolute and (b) normalized-for-estimated-fetal-weight (EFW) umbilical vein blood flow central values (UV-Q) from studies included in systematic review and our set of data. Straight lines (−): studies investigating UV-Q at the intra-abdominal portion of the umbilical cord; dashed lines (- -): studies investigating UV-Q at the free-floating portion of the umbilical cord. Different colors represent the first author’s name and the year of publication [18,28,33,34,35,36,37,38,39,40,41,42,43].

Figure 4

This figure represents umbilical vein blood flow volume (UV-Q) central values in low-risk populations in studies that investigated UV-Q in the intra-abdominal (IA) portion of the umbilical vein: (a) UV-Q absolute value; and (b) normalized for estimated fetal weight (UV-Q/EFW). Different colors represent the first author’s name and the year of publication [34,35,39,40,41,42,43].

Figure 5

This figure represents umbilical vein blood flow volume (UV-Q) central values in low-risk populations in studies that investigated UV-Q on the free-floating (FF) portion of the umbilical cord: (a) UV-Q absolute value; and (b) normalized for estimated fetal weight (UV-Q/EFW). Different colors represent the first author’s name and the year of publication [18,28,33,36,37,39,42].

Figure 6

(a,b) Umbilical vein blood flow (UV-Q) 5th, 50th, and 95th percentiles, both (a) absolute and (b) normalized for estimated fetal weight (UV-Q/EFW) computed with the same methodology (i.e., on a free-floating loop of umbilical vein, in low-risk population, and with the same formula). Different colors represent the first author’s name and the year of publication [3,28,33].