Low blood pressure during pregnancy

Low blood pressure during pregnancy: A detailed overview

Feeling a sudden weakness or dizziness when you stand up from a chair can be unsettling, but during pregnancy it is an extremely common phenomenon. A mild drop in blood pressure (hypotension) is a physiological norm, especially in the first half of pregnancy. It is the result of the remarkable adaptation of your cardiovascular system to the new state.

Why the pressure drops: Hormones and vessels at work

The main “conductor” of this process is the hormone progesterone. Its level rises sharply from the first weeks, and one of its key functions is the relaxation of smooth muscle. This is vital for the uterus so that it does not contract and can grow, but progesterone’s action extends throughout the body, including the walls of your blood vessels.

When vessels dilate, the overall resistance to blood flow falls, leading to a drop in blood pressure. Imagine a water supply system: if you widen all the pipes, the water pressure in them drops. At the same time, your body starts producing more blood, but in the early weeks the vasodilation occurs faster than the increase in blood volume, which causes hypotension. Usually the pressure reaches its lowest values in the second trimester, and by the end of the third it gradually returns to non‑pregnant levels.

Orthostatic hypotension: Enemy of sudden movements

Most often low pressure appears as orthostatic (postural) hypotension. This is a condition where pressure drops sharply when the body position changes from horizontal or sitting to vertical. Gravity causes blood to “pool” away from the head, and the relaxed vessels do not constrict quickly enough to compensate. The result – sudden dizziness, “darkening of vision” or even brief fainting. That’s why the main recommendation is to move smoothly.

Inferior vena cava syndrome

In the later stages of pregnancy (usually after week 20) another cause of pressure drop appears – mechanical. When you lie on your back, the heavy uterus can compress the inferior vena cava – the large vein that carries blood from the lower body to the heart. This significantly reduces cardiac output, leading to a sharp drop in pressure, shortness of breath, and strong discomfort. That’s why pregnant women are advised to sleep on their side, preferably the left.