What is hierarchy? Answer Wiki. A hierarchy is A body of persons or things ranked in grades, orders, or classes, one above another; specifically in Natural Science and Logic, a system or series of terms of successive rank (as classes, orders, genera, species, etc.), used in classification.  From the OED .
1 During the first 24 weeks of pregnancy, it's common for blood pressure to drop.  A decrease in blood volume can also cause blood pressure to drop. A significant loss of blood from major trauma, dehydration or severe internal bleeding reduces blood volume, leading to a severe drop in blood pressure.
The other answer is correct, but blood pressure does not drop very significantly. This is because the vessels get smaller, and as they get smaller and further away from the heart, the blood pressure remains nearly stable. The reason for this is because when fluids are pushed through smaller vessels, their pressure increases.