Reference Values for Blood Flow Velocity in the Uterine Artery in Normal Pregnancies from 18 Weeks to 42 Weeks of Gestation Calculated by Automatic Doppler Waveform Analysis

Zusammenfassung

Ziel: Die vorliegende Studie wurde mit dem Ziel durchgeführt, neue Normkurven für die mütterliche Herzfrequenz, die mittleren intensitätsgewichteten Flussgeschwindigkeiten (Vmean) und die Gefäßwiderständen (PI, RI) mithilfe einer automatisierten Hüllkurvenanalyse von der A. uterina zu erstellen. Material und Methoden: Eine prospektive Querschnittsstudie bei 921 normalen Schwangerschaften wurde zwischen 18 – 42 Schwangerschaftswochen durchgeführt. Die uterinen Blutflussgeschwindigkeiten wurden mittels farbkodierter gepulster Doppersonografie standardisiert abgeleitet. Die uterinen Dopplermessungen wurden 1 – 2 cm oberhalb der Kreuzungstelle der A. iliaca externa durchgeführt. Für die einzelnen Dopplerparameter der A. uterina erfolgte die Konstruktion von Referenzbändern basierend auf einer Wachstumsfunktion einer 4-parametrischen Klasse monotoner Funktionen, die durch kleinste Quadrateanpassung bestimmt wird. Ergebnisse: Ein signifikanter Anstieg der intensitätsgewichteten mittleren uterinen Blutflussgeschwindigkeiten wurden zwischen der 18. und 42. Schwangerschaftswoche beobachtet (Vmean = 43 cm/s bis 50 cm/s (p < 0,001). Die Pulsatilitäts- und Resistenzeindizes (PI, RI) zeigten mit zunehmendem Gestationsalter eine signifikante Abnahme (PI: 18. SSW: 0,89; 42. SSW: 0,65 und RI: 18. SSW: 0,45; 42. SSW: 0,35). Beim Vergleich der Plazentalokalisationen fanden sich keine signifikanten Unterschieden für den Pulsatilität- und den Resistenzindex. Die maternale Herzfrequenz fiel von 88 Spm auf 77 Spm (p < 0,001). Schlussfolgerung: Neue dopplersonografische Referenzkurven von den Blutflussgeschwindigkeiten der A. uterina und den Widerstandsindizes (PI, RI) konnten an einem Normalkollektiv errechnet werden. Die vorliegenden Normkurven können als Referenzwerte für den frühzeitigen Nachweis einer maternalen und fetalen Gefährdung herangezogen werden.

Abstract

Purpose: The goal of the present study was to establish new Doppler reference ranges for maternal heart rate, intensity-weighted mean blood flow velocities (Vmean) and impedance indices (PI, RI) for the uterine artery by automated waveform analysis. Materials and Methods: A cross-sectional prospective study of 921 low-risk pregnancies was performed at 18 – 42 weeks of gestation. Uterine blood flow velocities were derived with pulsed-wave color Doppler. Measurements were carried out 1 to 2 cm above the crossing of the uterine and external iliac arteries. 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. Results: A significant increase in intensity-weighted mean uterine blood flow velocities was observed at 18 – 42 weeks of gestation (Vmean = 43 cm/s to 50 cm/s (p < 0.001)). Reference curves for the pulsatility and resistance indices (PI, RI) significantly decreased with progressing gestation (PI: 18 weeks: 0.89; 42 weeks: 0.65 and RI: 18 weeks: 0.45; 42 weeks: 0.35). No significant PI and RI differences were observed when different placental locations were compared. The maternal heart rate decreased from 88 bpm to 77 bpm. Conclusion: Normal ranges for blood flow velocities and impedance indices in the uterine artery were established by Doppler ultrasound antenatal examinations of a large population of low-risk pregnancies. The data are proposed as reference curves to allow the early diagnosis of maternal and fetal risks.

Key words

doppler - reference values - regression function - uterine artery - pregnancy

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