Predicting the risk of pre-eclampsia and a small-for-gestational-age infant by quantitative assessment of the diastolic notch in uterine artery flow velocity waveforms in unselected women.

OBJECTIVES

To develop a new quantitative index, the notch depth index (NDI), to evaluate its association with the risk of pre-eclampsia and a small-for-gestational-age (SGA) infant and to compare its clinical usefulness with that of the uterine artery resistance index (RI) and the peak systolic to early diastolic velocity (A/C) ratio.

METHODS

Uterine artery color Doppler ultrasound was performed in 288 consecutive healthy pregnant women at 20.2 +/- 2.0 (range 16.0-23.9) weeks of gestation. The NDI represents the depth of the early diastolic notch divided by the maximal diastolic velocity.

RESULTS

Nine (3.1%) of the 288 women developed pre-eclampsia and 18 women (6.3%) delivered an SGA infant. The NDI was associated with subsequent onset of pre-eclampsia. The optimal cutoff value for the NDI in predicting pre-eclampsia was 0.14, giving a sensitivity, specificity and a positive predictive value (PPV) of 67, 92, and 22%, respectively. The PPV of the NDI was the largest of the three indices evaluated (12% for the RI and 16% for the A/C ratio). The relative risk for pre-eclampsia in women with values equal to or greater than the optimal cutoff values of the RI, A/C ratio and the NDI was 9.7 (95% confidence interval, 2.5-3.7), 19.2 (4.2-91), and 19.2 (5.1-71), respectively. The NDI of 0.14 improved the PPV of 18% determined by the presence of notches in bilateral uterine arteries. The optimal cutoff value of 0.14 for the NDI in predicting an SGA infant yielded a higher PPV (22%) than those for the RI (9%) and A/C ratio (12%).

CONCLUSIONS

The NDI value in the second trimester is associated with the later onset of pre-eclampsia, and is clinically more useful in predicting pre-eclampsia than the two conventional indices.