What is the substance that is significantly decreased as a change preceding preeclampsia?

In the context of preeclampsia, a notable change that occurs before the onset of the condition is the decrease in urinary calcium levels. This decrease is significant because calcium is essential for various physiological processes, including vascular function and regulation of blood pressure.

In a healthy pregnancy, there is often increased calcium retention and excretion, which supports fetal development and maintains maternal health. However, in women who develop preeclampsia, the physiological changes leading to decreased urinary calcium might indicate disturbances in calcium metabolism and regulation, which could contribute to the pathophysiology of the condition.

While other substances such as angiotensin II and renin play important roles in the regulation of blood pressure and fluid balance, they are not typically characterized by a significant decrease prior to the onset of preeclampsia. Thromboxane A2 is involved in platelet aggregation and vasoconstriction, and while its levels might be altered during preeclampsia, it does not specifically trend downward in the same way as urinary calcium as a precursor to the condition. Thus, the decreased urinary calcium serves as a relevant marker in the understanding and potential early identification of preeclampsia.