Anemia in late pregnancy induces an adaptive response in fetoplacental vascularization

Anemia during pregnancy may compromise fetal and newborn's health, however, little is known about how and when the fetoplacental vascularization is most vulnerable to anemia.

Using systematic and isotropic uniform random sampling, placental samples were collected from 189 placentas in a cohort study of Tanzanian women whose hemoglobin concentration was measured throughout pregnancy. Fetoplacental vessels and villi were defined as exerting either a transport or diffusion function. The vascularization patterns for transport and diffusion vessels and villi were assessed by stereology. Blood vessel length, surface area and diffusion distance as well as placental villi volume were calculated.

Anemia from a gestational age of 23 weeks was significantly associated with increased fetoplacental vascularization in vessels and villi compared to women who were non-anemic throughout pregnancy. Transport surface vessel area: 0.31 m² [95% CI: 0.18-0.55], P = 0.01; Transport villi volume 19.8 cm³ [95% CI: 6.37-33.2], P = 0.004, Transport vessel diameter 7.23 μm [95% CI: 1.23-13.3], P = 0.02. Diffusion vessel surface: 3.23 m² [95% CI: 1.55-4.91], P < 0.001 and diffusion villi volume: 29.8 cm³ [95% CI: 10.0-49.5], P = 0.003). Finally, all the measured transport vessel and villi significantly parameters and diffusion vessel surface, vessel diameter and diffusion distance were associated with birth weight.

Increased fetoplacental vascularization related to anemia from a gestational age of 23 weeks in pregnancy together with the association between fetoplacental vascularity and birth weight suggest that the timing of anemia determines the effect on fetoplacental vascularization and underlines the clinical relevance for proper development of fetoplacental vasculature.