Maternal Uterine Vascular Remodeling During Pregnancy

Abstract

This classification was proposed by Mulvany (86) and is further refined to include consideration of wall mass, which can increase (hypertrophy), decrease (hypotrophy), or remain unchanged (eutrophy). Various patterns of arterial remodeling are shown in FIGURE 1; see legend for additional detail and for consideration of how changes in crosssectional area, a two-dimensional quantity (e.g., m 2 ), relate to changes in wall mass, a three-dimensional quantity (e.g., m 3 ). Uterine Hemodynamics DuringPregnancy; Blood Flow Patterns and the Importance of Placentation Type Uterine vascular anatomyAn overview of comparative uterine vascular anatomy is presented in FIGURE 2, which describes and illustrates the uterine circulation in humans (FIGURE 2A), rodents (FIGURE 2B), and ungulates, such as sheep and pigs. Please see legend for additional detail.Uterine and placental blood flow during pregnancy Early (1953Early ( -1960 human studies by Assali et al (3, 4) and Metcalfe (78) utilizing the diffusion equilibrium principle (most often nitrous oxide, N 2 O) or electromagnetic flow probes placed directly on the uterine artery reported that total uteroplacental blood flow (UPBF) increases from a baseline value of 20-50 ml/min to 450-800 ml/min in singleton pregnancies, with values in excess of 1 l/min measured in twin pregnancy. Subsequent measurements of uterine artery blood flow with 133 Xe (106), placental metabolic clearance rate techniques (29) The clinical relevance of maternal uterine vascular adaptation during pregnancy is underscored by the fact that its aberrance is associated with several common gestational pathologies, including intrauterine growth restriction, gestational diabetes, and preeclampsia.In addition to the changes in vessel structure, uterine vascular reactivity is also altered during pregnancy, with the general pattern being one of reduced tone and enhanced vasodilation/blunted vasoconstriction (52,72,111,112,118). Space limitations preclude indepth consideration of the ionic and enzymatic mechanisms that underlie reactivity, but it is worth noting that, in vivo, uterine vascular resistance (and, therefore, blood flow) is ultimately determined by the combination of vessel size and reactivity.We also avoid examining the complex angiogenic mechanisms associated with implantation and placentation, other than to consider how hemochorial vs. epitheliochorial placentation influences uterine hemodynamics and vascular remodeling. Although the remodeling of spiral arteries by fetal trophoblast is considered, the main focus of this review is on upstream maternal uterine arteries and veins, since the processes involved in their remodeling have not been reviewed to date. Readers interested in endovascular trophoblast invasion and mechanisms underlying spiral artery remodeling are referred to several reviews on this subject (9, 31, 71, 101). Nomenclature Used to Describe Vascular RemodelingCircumferential remodeling is normally termed inward or outward to denote narrowing vs. widening of the vessel lumen. The ...

Maternal Vascular Physiology in Preeclampsia

“…Remodeling of these arteries refers to increases in their lumen (outward remodeling) and in their length (elongation). 94 In pregnant rats, the internal diameter of the main uterine artery increases, and the extent of this adaptation differs between the ovarian (30% increase) and cervical origins (80% increase) of the artery. 95 Pregnancy-associated changes in the lumen of the vascular wall have been attributed to vascular smooth muscle cell axial hypertrophy and hyperplasia.…”

“…95 Pregnancy-associated changes in the lumen of the vascular wall have been attributed to vascular smooth muscle cell axial hypertrophy and hyperplasia. 94,96 Elongation of the main uterine, arcuate, and radial arteries is evident in various species. In pregnant rats, the length of the main uterine artery at term is 2-to 3-fold greater compared with the length of the uterine artery from nonpregnant rats.…”

Alterations in maternal and fetal heart functions accompany failed spiral arterial remodeling in pregnant mice

“…1 Because WT and Rag2 −/− /Il2rg −/− mice had similar renal arterial velocities, a vessel arising close to or upstream of the ovarian artery, ovarian arterial study was not conducted. Uterine arterial velocity was estimated from vessels arising from the internal iliac (Fig 2A, B).…”

“…In women, these changes are attributed to an almost doubling of uterine arterial diameter accompanied by alternations in collagen and elastin. 1 Increasing uterine arterial flow, used with other tests to identify human fetuses at increased risk for adverse outcome, 28,29 is thought to reflect defective SA modification and increased downstream resistance. 30 Our data in Rag2 −/− / Il2rg −/− support this interpretation and expand it to show that altered maternal and fetal cardiac functions accompany and may precede the gd10-16 gains in uterine arterial flow velocity.…”

“…In species with hemochorial placentation, such as humans, uterine vascular changes include increased permeability, angiogenesis and structural remodeling of most spiral arteries (SA) to reduce vasoactivity and increase capacity. 1,2 In humans, inadequate modification of decidual and myometrial SA is often accompanied by preeclampsia (PE) and/or intrauterine growth restriction (IUGR). 3,4 SA remodeling is progressive and involves loss of vascular smooth muscle coat and elastic lamina, mural invasion by trophoblast cells that deposit nonvasoactive fibrinoid and transient replacement of vascular endothelial cells by intravascular trophoblast.…”