Z‐Score Reference Ranges for Umbilical Vein Diameter and Blood Flow Volume in Normal Fetuses

Abstract

Objectives To establish Z‐scores for the diameter and blood flow volume of the umbilical vein (UV) in normal fetuses. Methods This was a prospective study involving 907 normal fetuses. We measured the diameter (Duv) of two different segments of the UV (FUV: the free loop of the UV; FIUV: the fetal intra‐abdominal UV). Next, we calculated the blood flow volume (Quv). Z‐scores were created for both Duv and Quv using gestational age, femur length, and biparietal diameter as independent variables. Results We successfully acquired 858 (94.6%) normal fetal measurements. Between 20 and 39 weeks, the Duv of the FUV and FIUV increased from 0.38 to 0.80 cm and from 0.33 to 0.70 cm, respectively. The Quv of the FUV and FIUV increased from 32.66 to 381.88 ml/min and from 31.50 to 360.15 ml/min, respectively. Linear or quadratic regression models were best fitted between the parameters of UV and the independent variables. Z‐scores were successfully determined for both the Duv and Quv. Conclusions The calculation of Z‐scores for the Duv and Quv is simple by applying standard statistical methods. These Z‐scores may be useful to evaluate placental circulation and provide a rationale for monitoring and evaluating the prognosis of fetuses.

The abnormal umbilical venous–arterial index in the second half of pregnancy is associated with fetal outcome: A retrospective cross-sectional study

“…Our results showed that Duv, Vmax and Quv increased with GA, while UAPI decreased as pregnancy proceeded under normal circumstances. The alterations in Duv, Vmax, Quv and UAPI were consistent with previous studies on umbilical vein blood flow (1,11,13). Although the placental blood flow also increased with fetal body weight, the nQuv declined slightly with gestational age.…”

Umbilical vein blood flow: State‐of‐the‐art

“…A progressive and exponential increase in placental blood flow in the human fetus can be observed throughout gestation. Several studies [4][5][6][7][8][9][12][13][14]16,[27][28][29] obtained an estimate of the umbilical vein blood flow. 21,30 The absolute blood flow volume in umbilical vein increases around 7-fold in the second half of the pregnancy 6 (i.e., from 63 ml/ min at 20 weeks to 373 ml/min at 38 weeks 8 ) (Figure 5; data unpublished, presented at ISUOG World Congress 2022).…”

Confidence Intervals Versus Reference Intervals: Is There a Problem With the Study Entitled “Z‐Score Reference Ranges for Umbilical Vein Diameter and Blood Flow Volume in Normal Fetuses”

“…As an example, Figure 3 illustrates where I believe the reference interval lines should be placed in Figure 2F of the Wang study. 1 In summary, I would suggest the authors (1) correct the standard deviation equation for the umbilical vein diameter measured in the amniotic fluid, (2) explain how they know they were in the center of the umbilical vein for their measurements of the vein diameter, and (3) re-analyze their data and select the equations using fractional polynomial regression to compute the mean and standard deviation that represents the reference intervals. [2][3][4] Unless this is done, Z-score computations will not be accurate.…”

“…Figure 1F and H of the Wang study shows a "pulsatile" waveform of the umbilical vein. 1 This is highly unusual as the venous flow is "flat," except when the fetus is breathing. Why were these images selected as an example when umbilical venous flow is usually nonpulsatile?…”

“…Supplement 1 demonstrates the computations from the equations listed in Tables1 and 2from the Wang study 1. …”