BLOOD PRESSURE TO VASCULAR RESISTANCE RATIO ASSOCIATES WITH EMBRYONIC AND FETAL GROWTH

Objective: Mean arterial pressure and uterine artery Doppler pulsatility index (PI) and resistance index (RI) are considered indicators for maternal hemodynamic adaptation in pregnancy. To combine the clinical value of these parameters, this study evaluated their ratio in association with embryonic and fetal growth. Design and method: Data were obtained from an ongoing periconception cohort of women with a singleton pregnancy from 2010 to 2022. MAP, PI, and RI were measured at 7, 9, 11, 22 and 30 weeks gestational age, and their ratios were related to crown-rump length (CRL) and embryonic volume (EV), measured by three-dimensional ultrasound at 9 and 11 weeks, as indicators of embryonic growth using multiple linear regression, adjusting for potential confounders. Their association with fetal growth was assessed based on birthweight percentile groups: small-for-gestational age (SGA, <10th percentile), appropriate for gestational age (AGA, 10-90th percentile), and large-for-gestational age (LGA, >90th percentile). Results: In total, 481 women were included. The adjusted MAP/RI ratio at 9 weeks gestational age was associated with accelerated embryonic growth between 9 and 11 weeks: square root of CRL, beta=0.06 μm (95% CI 0.00; 0.13) and cube root of EV, beta=1.51 μm3 (95% CI 0.31; 2.71). This was also shown for adjusted MAP/PI ratio at 9 weeks and cube root of EV (beta=1.43 μm3; 95% CI 0.07; 2.78), but not square root of CRL (beta=0.06 μm; 95% CI -0.01; 0.13) between 9 and 11 weeks. At 22 weeks, the mean MAP/PI ratio was 84.2 for SGA, 98.3 for AGA, and 124.8 for LGA (P = 0.010), while for the mean MAP/RI ratio these values were 141.2, 154.6 and 182.1 (P = 0.024). Across pregnancy, SGA pregnancies demonstrated lower MAP/PI and MAP/RI ratios compared to AGA and LGA pregnancies, reaching significance in the second and third trimester (Figure 1). Conclusions: These findings suggest that the MAP/PI and MAP/RI ratios can serve as indicators of prenatal growth with the potential to predict SGA and LGA. This could facilitate earlier intervention and better anticipation, ultimately improving birth outcomes.