Indications for Analysis of Fetal Umbilical Artery Waveforms
· Multiple gestations- in evaluation of twins, an abnormally high S:D ration is frequently associated with IUGR (75%). In twin-twin transfusion syndrome the 'recipient' may have a lower S:D ratio than the donor twin.
· Rhesus incompatibility-
· Placental abruption- Increased umbilical vein blood flow is found in placental abruption and may take some time to return to normal after antepartum hemorrhage has ceased.
· Severe maternal illness-
· Hypertension- A reductions in diastolic flow velocity in the uteroplacental waveform has been reported. Hypertensive patients with normal uteroplacental S:D ratios have a better fetal prognosis than those with abnormal waveforms.
· Lupus anticoagulant syndrome- Abnormalities similar to those toxemia of pregnancy have been reported. Abnormal uterine artery S:D ratios are indicative of patients at risk of IUGR and fetal death.
· Sickle cell disease- Patients homozygous for sickle cell anemia have a high incidence of abnormal waveform ratios that correlate well with the presence of abnormalities are less prominent in the heterozygotes.
· Maternal diabetes mellitus- There is a rise of umbilical vein volume flow rate, probably representing part of the fetal macrosomia syndrome.
· Placenta previa- placenta previa may cause an increase in the S:D ratio and those with high ratios (>3) have a significantly increased risk of perinatal mortality and morbidity.
· Congenital fetal abnormalities- Fetuses with cardiac abnormalities and abnormal flow waveforms have a poor prognosis particularly with absent end diastolic flow. Fetal death frequently occurs in this group. Doppler is helpful in assessing prognosis and this planning management.
NB- Reversed flow in the umbilical artery is associated with poor outcome.