Figure 1.

Placental development in normal early pregnancy and in early pregnancy loss. Normal: The maternal spiral arteries are plugged with trophoblast cells until approximately 9 weeks of gestation in normal early pregnancies. This inhibits maternal blood flow into the intervillous space and any associated oxidative stress. Rather, the intervillous space is filled with serum transudate and nutrients to support the developing fetus. Early loss: Poor placentation associated with early pregnancy loss is characterized by limited trophoblast plug formation in the maternal spiral arteries and free flow of maternal blood into the intervillous space. This allows for oxidative damage to the extremely vulnerable placental villi.