Establishing reference values for mean notch depth index, pulsatility index and resistance index in the uterine artery at 16–23 weeks’ gestation Kayo Takahashi*, Akihide Ohkuchi*, Chikako Hirashima, Shigeki Matsubara and Mitsuaki Suzuki Department of Obstetrics and Gynecology, Jichi Medical University School of Medicine, Tochigi, Japan Abstract Aim: Our aim was to determine the reference values of indices of impedance to flow in uterine arteries at 16–23weeks, 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 16–23weeks. 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. Key words: early-onset pre-eclampsia, notch depth index, prediction, uterine artery Doppler. Introduction Doppler ultrasonography has been used to assess the indices of impedance to flow in uterine arteries to screen women at high risk for pre-eclampsia (PE) in the first and second trimester. 1 A systematic review and meta-analysis for the use of the uterine artery Doppler to predict PE and a small-for-gestational-age (SGA) infant revealed that: (i) the uterine artery Doppler provided a more accurate prediction when performed in the second trimester than in the first tri- mester; (ii) an increased pulsatility index (PI) with notching was the best predictor of PE, followed by bilateral notching (BN), and the positive likelihood Received: September 24 2011. Accepted: December 18 2011. Reprint request to: Dr Akihide Ohkuchi, Department of Obstetrics and Gynecology, Jichi Medical University School of Medicine, 3311-1Yakushiji, Shimotsuke-shi, Tochigi 329-0498 Japan. Email: okuchi@jichi.ac.jp *Both authors contributed equally to this research. doi:10.1111/j.1447-0756.2012.01864.x J. Obstet. Gynaecol. Res. Vol. 38, No. 11: 1275–1285, November 2012 © 2012 The Authors 1275 Journal of Obstetrics and Gynaecology Research © 2012 Japan Society of Obstetrics and Gynecology