What Causes Low Blood Pressure in Pregnancy?

Low blood pressure in pregnancy is normal. However, there may be other conditions that contribute to low blood pressure, including heart conditions, anemia, allergic reactions, dehydration, and more.

Blood pressure is the force of blood against the walls of arteries. When blood pressure is too low, also called hypotension, blood doesn’t reach the entire body. This can mean your cells don’t get enough oxygen and nutrients, waste products aren’t properly removed from the body, and organs might not function properly.

Low blood pressure is common. Healthy people who have low blood pressure within the normal range tend to live longer than those who have high blood pressure.

It is normal for women to experience low blood pressure in pregnancy. As long as the low blood pressure stays within a healthy range, your doctor may not be overly concerned. However, while it is normal, hypotension in pregnancy may also have specific causes.

Blood pressure is measured in millimetres of mercury (mmHg) and has two values:

• Systolic pressure – the pressure when the heart pumps blood out
• Diastolic pressure - the pressure of the blood between heart beats

Low blood pressure in pregnancy measures at 90/60 mmHg. Normal blood blood pressure is considered up to 120/80 mmHg. 

Other common symptoms of low blood pressure in pregnancy include:

• Nausea
• Lightheadedness or dizziness
• Feeling weak
• Fainting
• Blurred vision
• Confusion

This may happen when you stand up or change positions quickly, which is called orthostatic hypotension.

Low blood pressure in pregnancy is normal. This occurs because the central nervous system expands quickly. When this happens, blood pressure is likely to drop, though it usually returns to pre-pregnancy levels after birth.

There may be other conditions that contribute to low blood pressure, including:

• Heart conditions
• Allergic reactions
• Dehydration
• Bleeding
• Diseases like diabetes or thyroid disease
• Certain medications
• Extended bed rest
• Anemia
• Prolonged infection

Additionally, low blood pressure in pregnancy may be caused by:

Supine hypotensive syndrome of pregnancy

This condition, also called maternal hypotension syndrome, can occur when you are pregnant and sleep on your back or right side. The enlarged uterus presses on a main vein and reduces blood flow, leading to low blood pressure. 

Ectopic pregnancy

An ectopic pregnancy occurs when a fertilized egg implants outside the uterus. When it ruptures, women often have vaginal bleeding and abdominal pain. If you have substantial blood loss, you may feel faint, sweaty, and lightheaded, which can indicate dangerously low blood pressure.

Epidural or spinal anesthesia

During delivery, some mothers have an epidural or a Caesarean section. A side effect of these practices is low blood pressure, which may cause the mother to feel faint or nauseous. Your doctor will monitor and treat this side effect.

Your doctor will check your blood pressure during every prenatal appointment. Blood pressure is an important vital sign that doctors monitor during pregnancy.

It is normal to experience low blood pressure in pregnancy. Be sure to attend your regular appointments and to inform your doctor of your symptoms.

If symptoms appear with sudden bleeding, chest pain, severe headaches, or confusion, seek immediate medical attention. See your doctor if symptoms like fainting cause falls or happen at dangerous times, like while driving. 

Tests for low blood pressure in pregnancy usually involve a blood pressure cuff that pumps your arm to restrict blood flow. You can often find blood pressure test stations in pharmacies and clinics and you can purchase blood pressure test devices to monitor your pressure at home.

Sometimes your doctor may also do blood tests to check for low blood sugar or low red blood cells that can cause anemia. They may also do an electrocardiogram (ECG) or echocardiogram to check for heart-related problems.

Because low blood pressure in pregnancy is normal, your doctor may not prescribe medication unless serious or severe symptoms develop. The treatment will be to monitor symptoms and make lifestyle adjustments.

These might include:

• Drinking more water to prevent dehydration
• Wearing compression socks 
• Sitting up or standing up slowly 
• Raising the head of your bed or prop yourself up in bed with pillows 
• Sleeping on your left side to prevent blood flow restriction

If you have an epidural or Caesarean section, your doctor may use medications or specific techniques to help prevent serious low blood pressure from developing