Determination of Placental Weight Using Two-dimensional Sonography and Volumetric Mathematic Modeling

Abstract

An abnormally decreased placental weight has been linked to increased perinatal complications, including intrauterine fetal demise (IUFD) and fetal growth restriction (IUGR). Despite its promise, determining placental weight prenatally using three-dimensional systems is time-consuming and requires expensive technology and expertise. We propose a novel method using two-dimensional sonography that provides an immediate estimation of placental volume. Placental volume was calculated in 29 third-trimester pregnancies using linear measurements of placental width, height, and thickness to calculate the convex-concave shell volume within 24 hours of birth. Data were analyzed to calculate Spearman's rho (r (s)) and significance. There was a significant correlation between estimated placental volume (EPV) and actual placental weight (r (s) = 0.80, P < 0.001). Subgroup analysis of preterm gestations ( N = 14) revealed an even more significant correlation of EPV to actual placental weight (r (s) = 0.89, P < 0.001). Placental weight can be accurately predicted by two-dimensional ultrasound with volumetric calculations. This method is simple, rapid, and accurate, making it practical for routine prenatal care, as well as for high-risk cases with decreased fetal movement and IUGR. Routine EPV surveillance may decrease the rates of perinatal complications and unexpected IUFD.

Third trimester placental volume and biometry measurement: A method-development study

“…Ex vivo modelling identified the ellipse as the appropriate geometric volume for PV estimation, explaining why the 2D ellipse has a higher statistical correlation than the previously described shell (elliptical cylinder) method [19]. An elliptical est PV has previously been applied in the first trimester of pregnancy [25] but utilised est L and est W derived by method 2, shown here to be less correlated to true L and W than method 3 in the third trimester.…”

“…An elliptical est PV has previously been applied in the first trimester of pregnancy [25] but utilised est L and est W derived by method 2, shown here to be less correlated to true L and W than method 3 in the third trimester. Conversely, the shell est PV method was previously correlated to PW in a much smaller cohort (38 participants, with 23.7% overall failure rate) [19] compared to our validation cohort of 87 pregnancies (with 2.3e4.6% failure rate) in which we were unable to replicate the previously reported correlation between shell est PV and PW, despite establishing a constant relationship between PW and PV, with a tissue density close to 1.0 (as in liver [33]). Indeed, no method of est PW or est PV demonstrated statistical correlation with PW, although several approached statistical significance.…”

“…Based on an expected correlation of 0.68 between est PV and PV in term pregnancies and an up to 37.5% failure to obtain third trimester measurements [19] a minimum of 22 placentas would be required to detect a significant correlation of similar magnitude with power of 80% at the level of p < 0.05. Given the local proportion of pregnancies delivering within seven days of assessment for reduced fetal movements (32.6%, unpublished data) and a 10% loss to follow up rate, we estimated that at least 120 participants would need to be recruited to obtain sufficient matched in vivo and 2.…”

“…2A). Next the placental arc was measured as previously published [19] (Fig. 2B) and the est PV calculated from the concave convex shell formula (…”

“…However, no studies have examined the accuracy of these techniques, or whether there is any meaningful correlation between in utero sonographic placental biometry measurements and direct measurements of ex vivo placental size after delivery. In contrast, a 2D PV technique has been correlated to placental weight (PW) [19]. It is not known whether PW and PV are consistently related; therefore this correlation may prove inappropriate.…”