Breathing difficulties while lying down

Breathing difficulties in the supine position: Inferior vena cava syndrome

Sudden feeling of shortness of breath, dizziness and nausea that occur when you lie on your back — this is a classic and very frightening symptom, especially characteristic of the third trimester. This condition is called inferior vena cava compression syndrome (or aorto‑caval compression syndrome) and is purely a mechanical problem.

What happens when you lie on your back?

The inferior vena cava is a large blood vessel that runs to the right of the spine and is responsible for returning venous blood from the lower part of the body to the heart. When you lie on your back in late pregnancy, your heavy uterus presses on this vein, compressing it.

This leads to a sudden reduction in the amount of blood returning to the heart. As a result, cardiac output drops, arterial pressure falls, and your brain begins to experience a lack of oxygen, which manifests as the following symptoms:

• Sudden shortness of breath.
• Severe dizziness.
• Accelerated heart rate.
• Nausea and cold sweat.

The simplest solution

Although the symptoms are very unpleasant, the solution is extremely simple: just turn onto your side, preferably the left. This shifts the uterus away from the vein, restores normal blood flow, and the symptoms disappear almost instantly. Sleeping on the left side is considered optimal not only for preventing this syndrome but also for the best placental blood supply. Read more about comfortable and safe rest in the article "Sleep during pregnancy".