Larger First-Trimester Placental Volumetric Parameters Are Associated With Lower Pressure and More Flow-Mediated Vasodilation of the Fetoplacental Vasculature After Delivery.

Objective To explore the correlation between in vivo placental volumetric parameters in the first trimester of pregnancy and ex vivo parameters of fetoplacental vascular function after delivery. Methods In ten singleton physiological pregnancies, placental volume (PV) and uteroplacental vascular volume (uPVV) were measured offline in three-dimensional ultrasound volumes at 7, 9, and 11 weeks gestational age (GA) using Virtual Organ Analysis and Virtual Reality. Directly postpartum, term placentas were ex vivo dually perfused and pressure in the fetoplacental vasculature was measured to calculate baseline pressure (pressure after a washout period), pressure increase (pressure after a stepwise fetal flow rate increase of 1 mL/min up to 6 mL/min) and flow-mediated vasodilation (FMVD; reduction in inflow hydrostatic pressure on the fetal side at 6 mL/min flow rate). Correlations between in vivo and ex vivo parameters were assessed by Spearman's correlation coefficients (R). Results Throughout the first trimester, PV was negatively correlated with pressure increase (R-growth = -0.84) and, at 11 weeks GA, also positively correlated with FMVD (R = 0.89). At 7 weeks GA, uPVV and uPVV/PV ratio were negatively correlated with pressure increase (R = -0.58 and R = -0.81, respectively) and positively correlated with FMVD (R = 0.62 and R = 0.90, respectively). Discussion Mainly in the early first trimester, larger placental volumetric parameters are associated with lower pressure and more FMVD in the fetoplacental vasculature after delivery. This may suggest that larger and/or more vascularized placentas in early pregnancy have better adaptive mechanisms and possibly lead to better pregnancy outcomes.