Blood Flow Velocity Waveforms of the Umbilical Artery in a Normal Population: Reference Values from 18 Weeks to 42 Weeks of Gestation

Abstract

Purpose: The aim of the present study was to calculate new Doppler reference ranges for systolic, intensity-weighted mean, and end-diastolic blood flow velocities (V_max, V_mean, V_min) and fetal heart rate and impedance indices (PI, RI) of the umbilical artery by automatic waveform analysis.

Materials and Methods: A cross-sectional prospective study of 1926 low-risk pregnancies was performed at 18 – 42 weeks of gestation. The measurements were carried out in the region of a free floating loop of cord. Reference ranges for the individual measuring parameters were constructed based on a growth function from a four-parameter class of monotonic continuous functions according to the smallest square principle. The intraobserver reliability was also assessed.

Results: A significant increase in umbilical blood flow velocity was observed at 18 – 42 weeks of gestation (V_max = 33.7 cm/sec to 65 cm/sec (p < 0.001), V_mean = 18.2 cm/sec to 38.7 cm/sec (p < 0.001) and V_min = 8.2 to 31 cm/sec (p < 0.001). Reference curves for the pulsatility and the resistance index were associated with significant decreases with increasing gestational age (PI: 18 weeks: 1.3; 28 weeks: 1.1; 42 weeks: 0.8 and RI: 18 weeks: 0.7; 28 weeks: 0.6; 42 weeks: 0.5). The fetal heart rate decreased from 147 – 134 bpm. The intraobserver reliability was low, but of no clinical relevance.

Conclusion: The reference ranges for blood flow velocities and resistance indices in the umbilical artery calculated by the authors serve as the basis for Doppler ultrasound antenatal examinations in a normal patient population and enable the early diagnosis of fetal risk.

Zusammenfassung

Ziel: Die vorliegende Studie wurde mit dem Ziel durchgeführt, neue Normkurven für systolische, intensitätsgewichtete mittlere und enddiastolische Flussgeschwindigkeiten (V_max, V_mean, V_min), für die fetale Herzfrequenz und die Gefäßwiderstände (PI, RI) mithilfe einer automatisierten Hüllkurvenanalyse von der A. umbilicalis zu erstellen.

Material und Methoden: Eine prospektive Querschnittsstudie bei 1926 normalen Schwangerschaften wurde zwischen 18 – 42 Schwangerschaftswochen durchgeführt. Die Dopplermessungen wurden im Bereich einer freien Nabelschnurschlinge durchgeführt. Für die einzelnen Dopplerparameter der A. umbilicalis erfolgte die Konstruktion von Referenzbändern basierend auf einer Wachstumsfunktion einer 4-parametrischen Klasse monotoner Funktionen, die durch kleinste Quadrate-Anpassung bestimmt wird.

Ergebnisse: Ein signifikanter Anstieg der umbilikalen Blutflussgeschwindigkeiten wurde zwischen der 18. und 42. Schwangerschaftswoche beobachtet (V_max = 33,7 cm/s bis 65 cm/s (p < 0,001), V_mean = 18,2 cm/s bis 38,7 cm/s (p < 0,001) und V_min = 8,2 bis 31 cm/s (p < 0,001). Die Pulsatilitäts- und Resistenz-Indizes (PI, RI) zeigten mit zunehmendem Gestationsalter eine signifikante Abnahme (PI: 18 SSW: 1,3; 28 SSW: 1,1; 42 SSW: 0,8 und RI: 18 SSW: 0,7; 28 SSW: 0,6; 42 SSW: 0,5). Die fetale Herzfrequenz fiel von 147 auf 134 Spm (p < 0,001). Die Intraobserver-Reliabilität war niedrig und ohne statistische Relevanz.

Schlussfolgerung: Neue dopplersonografische Referenzkurven von den Blutflussgeschwindigkeiten der A. umbilicalis und den Widerstandsindizes (PI, RI) konnten an einem Normalkollektiv errechnet werden. Die vorliegenden Normkurven können als Referenzwerte für den frühzeitigen Nachweis einer fetalen Gefährdung herangezogen werden.

Key words

ultrasound color Doppler - fetus - umbilical artery - obstetrics - reference values

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