Establishing reference values for mean notch depth index, pulsatility index and resistance index in the uterine artery at 16-23 weeks' gestation.

AIM

Our aim was to determine the reference values of indices of impedance to flow in uterine arteries at 16-23 weeks, and to evaluate the effects of these indices for predicting early-onset pre-eclampsia (EO-PE), which was defined as PE with onset at <32 weeks.

METHODS

During 2004 to 2008, 1536 women with a singleton pregnancy were recruited into a prospective cohort study at 16-23 weeks. The mean notch depth index (mNDI), mean pulsatility index (mPI) and mean resistance index (mRI) were calculated.

RESULTS

Early-onset pre-eclampsia occurred in 16 (1.0%). The 80th, 90th, 95th and 97.5th percentiles of the mNDI at 16-23 weeks were determined. Normal reference ranges of the mPI and mRI were constructed, and individual standard deviation scores (SDS) of the mPI and mRI were calculated. The area under the receiver-operating characteristics curves (AROC) of the mNDI, mPI, mRI and bilateral notching (BN) for predicting EO-PE were 0.807, 0.809, 0.782 and 0.798, respectively. For predicting EO-PE, a mNDI of the 90th percentile, mPI-SDS of 1.383, mRI-SDS of 0.975 and BN yielded sensitivities (specificities) of 0.688 (0.886), 0.750 (0.889), 0.813 (0.809) and 0.750 (0.845) with positive likelihood ratios and 95% confidence intervals of 6.0 (4.2-8.6), 6.8 (4.9-9.3), 4.3 (3.3-5.5) and 4.9 (3.6-6.6), respectively.

CONCLUSIONS

We established the reference values for mNDI, mRI and mPI at 16-23 weeks. The positive likelihood ratios of mNDI and mPI for predicting EO-PE showed moderate screening performances, indicating mNDI or mPI in the second trimester could assist to find high risk women with the subsequent onset of EO-PE.