Low blood pressure, or hypotension, occurs when the force of blood pushing against artery walls is lower than the typical range, generally considered below 90/60 mmHg. This decrease is a common physiological adjustment during pregnancy and is usually not a sign of a problem. The drop most frequently begins in the first trimester and reaches its lowest point around the middle of the second trimester. This temporary change often resolves on its own before the third trimester.
Physiological Causes of Low Blood Pressure
The mechanisms behind this pressure drop are driven by hormonal and circulatory system transformations. The hormone progesterone, which rises rapidly in early pregnancy, acts as a smooth muscle relaxant. This relaxation causes the walls of the blood vessels throughout the body to widen, a process known as vasodilation. This widening significantly increases the overall capacity of the circulatory system.
While the body simultaneously increases blood volume to support both the pregnant person and the growing fetus, the vessels expand at a faster rate than the blood volume increases. This mismatch in the volume of blood relative to the expanded space available in the vessels results in a net decrease in pressure. The heart must also work harder to circulate this increased volume, but the relaxed, wider vessels offer less resistance to blood flow, contributing to the lower reading.
In the third trimester, physical pressure from the enlarging uterus can also contribute to temporary drops in blood pressure. When lying flat on the back, the heavy uterus can compress the vena cava, the large vein that returns deoxygenated blood to the heart. This compression reduces the amount of blood returning to the heart, which lowers the output and causes a drop in systemic blood pressure.
Identifying Common Symptoms
The reduced blood flow to the brain associated with hypotension often manifests as lightheadedness or dizziness. This is particularly noticeable when changing positions quickly, such as rising from a chair or standing up from lying down, a phenomenon known as orthostatic hypotension. Affected individuals may also experience fatigue that seems disproportionate to their activity level.
Other common signs include mild nausea and temporary blurring of vision. In more pronounced episodes, a person may feel faint or experience syncope, which is a temporary loss of consciousness. These symptoms signal that blood flow to the brain is momentarily insufficient.
Practical Strategies for Daily Management
Managing the symptoms of low blood pressure focuses on adjustments that help stabilize blood flow and volume. Increasing fluid intake is important, as dehydration reduces blood volume and can exacerbate hypotension. Aiming for at least eight to ten glasses of water daily helps maintain a healthy circulatory volume.
Dietary modifications can also be beneficial, starting with eating smaller, more frequent meals throughout the day. This approach prevents large drops in blood sugar and blood pressure that can follow a substantial meal, a condition known as postprandial hypotension. Increasing salt intake slightly may be recommended by a healthcare provider, as sodium helps the body retain water, thereby boosting blood volume.
Positional changes are another effective strategy for preventing symptomatic drops in pressure. Individuals should practice rising slowly from a sitting or lying position to allow the body’s circulatory system time to adjust. Avoiding standing motionless for long periods helps prevent blood from pooling in the lower extremities. When lying down in the later stages of pregnancy, sleeping on the left side is advised to relieve pressure on the vena cava and promote better blood return to the heart.
When to Seek Medical Guidance
While low blood pressure is often benign in pregnancy, certain symptoms warrant medical evaluation. Persistent or frequent fainting episodes pose a risk of injury from falling and should be reported immediately. Any low blood pressure symptoms accompanied by chest pain, a severe headache, or confusion also require immediate attention. The provider may investigate underlying issues contributing to hypotension, such as anemia or infection. Regular prenatal appointments monitor blood pressure trends and ensure the health of both the pregnant person and the developing fetus.