Under which condition are spiral arteries maximally dilated?

Spiral arteries are crucial for providing optimal blood flow to the placenta and, subsequently, the developing fetus. They undergo a transformation during pregnancy that includes remodeling and dilation, which ensures adequate perfusion. Under normal pregnancy conditions, these arteries reach their maximum dilation because the physiological changes associated with pregnancy, such as increased blood volume and hormonal changes, promote vasodilation. This state of dilation is essential for meeting the metabolic demands of the placenta and ensuring proper fetal development.

In contrast, during labor and contraction, the spiral arteries may experience temporary constriction due to increased uterine pressure, which is not conducive to maximal dilation. In cases of hypertension, the blood vessels, including spiral arteries, may be constricted rather than dilated, compromising blood flow to the placenta and potentially affecting fetal health. Therefore, it is the normal pregnancy conditions that ideally support the maximum dilation of spiral arteries, facilitating effective placental blood flow.