Doppler Ultrasound provides a non-invasive method for the study of fetal haemodynamics. Investigation of uterine and umbilical arteries gives information on the perfusion of the uteroplacental and fetoplacental circulation respectively. However Doppler studies of various or selected fetal parts or organs are very valuable in detecting the haemodynamic rearrangements that occur in response to fetal disease and fetal hypoxia
Uterine arteries Doppler
In pregnancies complicated by pre-eclampsia and or intrauterine growth restriction, impedance to flow in the uterine arteries is increased. Studies in women with hypertensive disease in pregnancy have shown that in those with increased impedance, increased resistance index or the presence of an early diastolic notch compared to hypertensive women with normal flow velocity waveforms, there is a higher incidence of pre- eclipse, intrauterine growth restriction, emergency Caesarean section, placental haemorrhage and abruption. There are also a tendency for a shorter pregnancy, pre term labour and an overall of poor perinatal outcome. (Nicolaides 2000)
Umbilical arteries Doppler
Similarly there is increased impedance in the umbilical arteries in pre- eclampsia and intra uterine growth restriction cases. This increase in impedance is become evident only when at least 50- 70% of the placental vascular bed is obliterated. In extreme cases there is an absent or a reversal of the end diastolic frequencies. This is of courses is associated in extreme cases with high perinatal morbidity and mortality. Therefore abnormal waveforms of the umbilical arteries found while monitoring babies with intrauterine growth restriction are an early sign of fetal compromise. It was also found that abnormalities of the umbilical artery Doppler preceded hypoxaemia and the fetal heart changes found on the mother’s cardiotocographic (CTG) monitoring of her baby in a large proportion of cases.
Fetal Middle Cerebral Artery (MCA) &Aorta Doppler
Doppler studies of the MCA are also a useful tool in pre- eclampsia and fetal intra- uterine growth restriction but perhaps not as much of use in the diabetic pregnancies. Maternal diabetes mellitus is associated with an increased risk of fetal loss as there is an association between maternal hyperglycaemia and fetal acidaemia. However there is no evidence of redistribution the fetal circulation as seen in cases of pre- eclampsi and intra uterine growth restriction with decreased Pulsatility Index (PI) in the middle cerebral artery and an increased PI in the decending thoracic aorta.
Therefore Doppler assessment of the placental circulation plays an important role in screening for impaired placentation and its association with pre-eclampsia, intrauterine growth restriction and perinatal death. Assessment of the fetal circulation is essential if we are to understate the pathology and the physiology of the different pregnancy complications, diseases and their correct clinical management.
Second & Third Trimester
Find out more about the following scans:
|Dating & Fetal Viability Scans||Vasa Praevia Screening||Pregnancy Scan|
|Nuchal Scan||3D - 4D Baby Scan||Diagnostic Scans|
|Fetal Anomaly Scan||Reassurance Scan||Pelvic Ultrasound Scans|
|Fetal Presentation Scan||Gender Scan||Cervical Length Scan|