Farbkodierte Dopplersonographie — Normwerte des Widerstandsindex in Abhängigkeit vom Gestationsalter

Abstract

The examination of fetal circulation by means of Doppler ultrasound has clinical potential. In order to use the indices that characterize the waveform, it is important to establish reference ranges throughout pregnancy and to determine the natural variations. This paper sets out to fulfill these requirements. The study was performed in 139 patients with singleton pregnancies between 29 and 41 weeks’ gestation. Patients with no previous obstetric complications and no apparent medical problems were approached at the time of their visit to the antenatal clinic. All examinations were performed by a single observer. A 3-MHz pulsed waved duplex Doppler ultrasound instrument was used (Quantum 2000; Siemens, Erlangen, Germany). Doppler blood flow velocity waveforms in the umbilical artery, fetal aorta and middle cerebral artery were recorded. For each artery, reference ranges and a standard curve were performed for the resistance index (RI). The RI of the umbilical and the middle cerebral artery showed a continuing fall during gestation, but the resistance index of the fetal descending aorta did not change during gestation. The finding that the RI changes as gestation progresses indicates that fetal circulation increases throughout pregnancy. This suggests a decreasing placental resistance during normal gestation. Study of fetal circulation may identify patients at risk of developing severe disorders, thus allowing possible preventive therapy. Knowledge of the reference ranges helps to discriminate between a normal situation and mild or severe forms of disease.

Zusammenfassung

Die farbkodierte Dopplersonographie hat die Geburtshilfe in den letzten Jahren mit Erkenntnissen über die Strömung des Blutes im fetoplazentaren Kreislauf bereichert. In der prospektiven Untersuchung wurden anhand eines Normalkollektivs von 139 Schwangeren Normkurven für den Verlauf des Resistenzindex (RI) erstellt. Es wurden die 10., 50. und 90. Perzentile von der 29. bis 41. SSW berechnet. Die Untersuchungen erfolgten mit dem farbkodierten Dopplerultraschallgerät Quantum 2000 (Fa. Siemens). Die aufgezeichneten Normkurven entsprechen der physiologischen Anpassung des fetalen Kreislaufs im Laufe der Schwangerschaft. Im klinischen Alltag ermöglicht ein Vergleich der Meßwerte mit Normwerten für die entsprechende SSW eine Abgrenzung von physiologischen zu pathologischen Blutflußverhältnissen.