OBJECTIVE The nomogram of blood velocity flow resistance of the spiral arteries was built at 13-25 gestational weeks. Thereafter, by using the nomogram we tried to assess the results of the color Doppler examination of the uteroplacental circulation at the second trimester to predict pregnancy-induced hypertension (PIH) and small-for-gestational-age (SGA). METHODS Two groups of patients were studied. Group 1, for the establishment of the nomogram, included 175 uncomplicated pregnancies with gestational ages ranging from 13-25 weeks. The Doppler flow waveforms of the spiral arteries were measured once for each pregnancy in the studies. Group 2 consisted of 305 singletons selected consecutively for prospective study to confirm the occurrence of PIH or SGA. They were scanned twice for the measurements of the spiral artery waveforms at 13-19 and 20-25 weeks, respectively to test which gestational weeks interval in the nomogram is most sensitive in predicting PIH and SGA. RESULTS The 5th, 50th and 95th percentiles of the pulsatility index (PI) values of the nomogram at the second trimester were used as the cut-off points to predict pregnancies complicated with SGA or PIH at delivery. Using the receiver operator curve, the 50th percentiles of the PI values of the nomograms were chosen as predictives for the development of PIH and SGA. At 13-19 gestational weeks, the specificities in predicting PIH and SGA were 50.71% and 49.82%, respectively, and the sensitivities were 52.00% and 50.00%, respectively. The calculated Cohen's Kappa statistics were 0.008 and 0.001, respectively in predicting PIH and SGA. At 20-25 gestational weeks, the specificities in predicting PIH and SGA were 49.64% and 49.46%, respectively, and the sensitivities were 56.00% and 57.14%, respectively. The calculated Cohen's Kappa statistics were 0.017 and 0.022, respectively in predicting PIH and SGA. CONCLUSIONS The measurements of uteroplacental blood flow velocity waveforms at the second trimester are not sensitive enough to be an early screening tool for PIH and SGA in the low risk, non-selected pregnancy population. The fact suggests that in most gravidas complicated with PIH and SGA, the physiological process of trophoblastic invasion in the spiral artery was not prevented before the 25th gestational week.