Umbilical artery pulsatility index in early pregnancies with chromosome anomalies

The aim of our study was to obtain measurements of the umbilical artery pulsatility index in pregnancies before invasive procedures for prenatal diagnosis, to investigate its potential prognostic value in predicting chromosomal abnormalities. A prospective study. Nine hundred and twenty-four consecutive women with singleton pregnancies between 10 and 18 weeks of gestation who underwent chorionic villus sampling (n = 385) or genetic amniocentesis (n = 539). All Doppler measurements were obtained by a single investigator before the invasive procedure. Pregnancies where structural malformations were detected by ultrasound were excluded. Twenty-six fetuses with chromosomal anomaly, including 12 with trisomy 21, were diagnosed. Using the 90th centile in umbilical artery pulsatility index values as a cut-off for trisomy 21 the detection rate was 66.6%, with a specificity of 90.4% and a positive predictive value (defined as the proportion of unaffected individuals with positive results, l-specificity) of 8.8%. However, with this cut-off the false positive rate was 9.6%. All 19 chromosomally normal pregnancies in which a fetal loss occurred after the procedure had a normal umbilical artery pulsatility index before it was carried out. These preliminary data suggest that trisomic fetuses have an abnormally increased umbilical artery pulsatility index in early pregnancy. Because the number of cases is too small to draw any firm conclusions, the use of a single measurement for screening purposes needs to be confirmed by further investigation and the clinical significance of reference curves of normal values in the detection of pathological conditions has still to be determined. The potential of umbilical artery pulsatility index as an additional parameter along with others previously established for Down's syndrome screening, such as nuchal oedema, needs to be explored further.