Figure 5. Scheme illustrating our novel hypothesis on pathophysiological interpretation of branching angles and tortuosity of villous branches in positions bT0 and bT1 of human placentas.

The proposal starts with the widely accepted early origin of IUGR as insufficient remodeling of uterine spiral arteries (A). Due to rheologic disturbance caused by this insufficient remodeling of uterine spiral arteries, branching angles (mpa) in position bT0 become larger (B; c.f. Fig. 6). For reasons that are currently unknown some placentas cannot compensate this rheologic disturbance and develop into IUGR placentas. In contrast, other placentas with insufficient remodeling of uterine spiral arteries (and, thus, rheologic disturbance and large branching angles at position bT0) develop highly tortuous branches in position bT1 as morphological correlate of successful compensation of rheologic disturbance (C). As a result this subset of placentas (i) shares some morphological characteristics with IUGR placentas (i.e., large branching angles in position bT0; c.f. Fig. 3) and (ii) shows certain morphological characteristics that were neither found in IUGR placentas nor in placentas with sufficient remodeling of uterine spiral arteries (i.e., higher mean tortuosity of the branches in position bT1, higher length of the branches in position bT1 as well as higher mean surface area and higher mean volume of the branches in positions bT0 and bT; c.f. Fig. 4). Because of this successful compensation of rheologic disturbance these placentas present as clinically normal, but are morphologically distinct from other clinically normal placentas in which no insufficient remodeling of uterine spiral arteries occurred.