OP15.06: Ultrasound prediction of uterine scar dehiscence during pregnancy in patients with a previous C-section

Abstract

(UtR), and estimate the fraction of CO distributed to the uteroplacental circulation during the second half of pregnancy. Methods: Fifty-three low risk-pregnancies were evaluated longitudinally at approximately 4-weekly intervals from 22 weeks until term (a total of 253 observations). Mean arterial blood pressure (MAP), CO and SVR were measured using impedance cardiography, and the uterine artery blood flow velocities and diameter using Doppler and B-mode ultrasonography, respectively. Quta of both uterine arteries was estimated as the product of time-averaged intensity weighted mean velocity and cross-sectional area of the uterine artery. UtR was calculated as: MAP/sum of right and left Quta. Results: CO increased from 5.5 to 5.8 L/min (p = 0.006) despite a significant increase in SVR from 1046 to 1135 dyne s cm-5 (p = 0.0077) during 22–40 weeks. The UtR decreased from 0.26 to 0.13 mmHg/mL/min (p < 0.00001) and the total utero-placental blood flow more than doubled during the same period increasing from 299 ml/min to 673 ml/min which represented 5.6% to 11.7% of the maternal CO. Conclusion: We have established longitudinal reference intervals for the fraction of maternal CO distributed to the utero-placental circulation at 22–40 weeks of gestation. Increments in uteroplacental blood flow are relatively higher than that of the CO in the second half of pregnancy suggesting redistribution of maternal circulation due to continuous reduction in UtR.