Abstract
To construct reference ranges for spiral artery (SA) flow velocities and examine the possibility to predict intra uterine growth restricted (IUGR) fetuses, pregnancy-induced hypertension (PIH) and/or preeclampsia. Spiral artery flow velocity measurements were performed using Color Doppler between 11 to 13 + 6, between 14 to 17 + 6 and between 18 to 24 weeks of gestation, each measurement was performed twice. Spiral artery flow velocities were analyzed with multilevel modeling: individual regression curves were estimated and combined to obtain the reference intervals for SA flow velocities in normal pregnancies. Mann-Whitney U tests was used to compare the deviation from expected flow velocity between normal and complicated pregnancies. One hundred and eight pregnancies were included; 4 pregnancies were complicated with preeclampsia, 10 pregnancies with IUGR fetuses (<P10) and 7 with PIH. In the uncomplicated pregnancies, systolic/diastolic (SD) ratios, resistance index (RI) and pulsatility index (PI) decreased progressively with advancing gestational age. The best fits for SD, RI and PI versus gestational age were linear regression equations. According to these equations, the mean predicted SD ratio decreased from 1.75 at 11 weeks of gestation (P5-P95: 1.32-2.17) to 1.48 at 24 weeks of gestation (P5-P95: 1.01-2.20). The predicted RI en PI showed similar decrement: mean RI from 0.44 (P5-P95: 0.26-0.60) at 11 weeks of gestation to 0.34 (P5-P95: 0.15-0.50) at 24 weeks of gestation, mean PI from 0.59 (P5-P95: 0.31-0.75) at 11 weeks of gestation to 0.40 (P5-P95: 0.11-0.66) at 24 weeks of gestation. The Mann-Whitney tests found no difference in PI, SD-ratio or PI in pregnancies complicated by PE and IUGR fetuses. However, significantly lower RI, PI and SD-ratio were found preclinically in pregnancies complicated by PIH. Spiral artery flow velocities decrease progressively with advancing gestational age. Reference ranges for SA blood velocities are wide and early measurements of PI, RI or SD-ratios are not sensitive enough to predict preeclampsia, PIH or IUGR fetuses. The significantly lower spiral artery impedance values preceding pregnancies complicated by PIH are likely caused by a hyperdynamic circulation in women with preexistent hypertension.
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