Supine Hypotension Syndrome

During pregnancy, lying flat on your back can worsen certain pregnancy symptoms such as heartburn and shortness of breath. It can also cause your blood pressure to drop. When your blood pressure falls from lying on your back during pregnancy, it’s called supine hypotension syndrome.

Supine is a medical term for lying flat on your back. Hypotension is low blood pressure. When you’re pregnant, and you lie flat on your back, the weight of the baby and your uterus press down on your spine and abdominal organs. The pressure can squeeze two of the largest blood vessels in your body – the aorta and the inferior vena cava.

Pressure on the aorta or vena cava can affect your circulation or the flow of blood in your body. The flow of blood returning to your heart may slow down. The amount of blood your heart pumps out may decrease. Your blood pressure can fall. It can also interfere with the flow of blood to your uterus and baby.

Blood Pressure

As your heart beats, it pumps blood to the rest of your body. Each pump sends the blood out with force. The force of the blood through your arteries is your blood pressure. 

Two numbers measure blood pressure. The systolic pressure is the top number, and the diastolic pressure is the bottom number. Healthy blood pressure measures less than 120 millimeters of mercury (mm Hg) over 80 mm Hg. 

When you're pregnant, the hormones dilate or expand the blood vessels and open up additional vessels for more circulation. So, your blood pressure may naturally go down a little bit. Your blood pressure can also go up or down during the day, depending on your activity. It may go down when you're resting or up when you're active, excited, or stressed.

Symptoms

When lying flat on the back, approximately 10% of expecting women experience symptoms of supine hypotension within three to ten minutes. The symptoms include:

• Turning pale
• A lower heart rate (bradycardia)
• Sweating
• Nausea
• Dizziness
• Weakness
• Shortness of breath
• Feeling faint

Risk Factors

As your pregnancy progresses, your uterus and baby grow and weigh more. It can lead to some squeezing of the vessels, but you may not feel the effects. Not everyone does. However, you may have more of a risk for encountering supine hypotension if:

• You are over 20 weeks along.
• Your uterus is large and heavy.
• You or your baby are in a position that may press on the blood vessels.
• You have a lot of amniotic fluid.
• You are carrying more than one baby.
• You are overweight or obese.
• You have a heart condition.
• Your collateral circulation system (the extra pregnancy blood vessels) is not working well enough.

Treatment

If you’re home and you feel symptoms of low blood pressure while you’re lying down, you should:

• Change your position.
• Turn onto your left side.
• Avoid lying flat on your back.
• If it continues to happen, call your doctor. 

If you are in the hospital, having a test, in an emergency situation, or in labor, the healthcare team may treat you by:

• Changing your position.
• Moving or tilting you to your left side.
• Giving you oxygen.
• Elevating your head.
• Moving your uterus over to the side.
• Medically or surgically treating or removing the underlying cause.
• Delivering the baby.

Concerns

During pregnancy, supine hypotension syndrome is a possibility whenever there’s a chance you might be lying flat on your back. Here are some concerning situations.

• Visiting the dentist
• Exercising on your back after 20 weeks
• Sleeping flat on your back from mid-pregnancy on
• Going for an MRI or other tests where you may have to lie on your back
• Suffering a trauma such as a car accident where you need to go on an emergency backboard.
• Lying on your back during labor
• Lying on your back during a c-section

Complications

Pressure on the main blood vessels can lead to an interruption in your blood flow. When the blood does not return from the lower body back to the heart the way it should, it can back up in the veins of your lower body. If the blood flow is reduced or blocked for too long, it can cause complications such as:

• Swelling (edema) in your lower body
• Hemorrhoids
• Varicose (swollen) veins in your legs
• Varicose veins in your vulva
• A higher risk for blood clots in the lower extremities (deep vein thrombosis)

In the most severe and rare cases, it can lead to:

• Shock  
• Loss of consciousness in a mother
• Less oxygen to the placenta
• Slow growth in the baby
• Death of a mother 
• Stillbirth

Tips

To prevent supine hypotension, you can try not to lie flat on your back. Here are some tips.

• Once you’re in your second trimester, you should avoid exercises that have you lie on your back, including some yoga and Pilates poses. Check for pregnancy modifications or other physical activities you can do instead. 
• Sleeping on your back in the second and third trimester is not recommended. Strategically placed pillows can relieve pressure on your blood vessels and help you sleep more comfortably on your side. You can also sleep up on an angle (incline) with your head and upper body higher than your lower body. However, there is no need to panic if you wake up on your back because you rolled over while you were sleeping. Chances are you’ll wake up and move if something isn’t right.
• If you are on your back and you suddenly feel dizzy or strange, change your position. You can turn onto your side (left side) or sit up.
• Lying on your side can make your hips feel sore. Try to find a comfortable position or use pillows or a mattress topper to ease the pressure on your hips. You can also use ice or heat to help relieve sore hips.
• Be careful standing up if you feel dizzy or faint while lying down. You could fall down.
• If you’re going to the dentist, to get a massage, or any other place where you might be lying down, say that you’re pregnant and be sure not to lie flat. Pregnancy is not always obvious, especially in the second trimester.
• You don’t have to lie on your back during labor. As long as you’re not having any complications and it’s safe, you can use multiple labor positions. 

Other Causes of Low Blood Pressure

Besides supine hypotension and the natural change in circulation from pregnancy hormones, low blood pressure during pregnancy can have other causes. It may be due to:

• Standing up too quickly
• Dehydration
• Some medications
• Anemia
• Heart and circulation problems
• An infection
• Bed rest
• Loss of blood
• Abdominal tumors or masses
• An ectopic pregnancy

A Word From Verywell

If your blood pressure goes down a little during pregnancy, you usually don't have to worry. A slight drop in blood pressure is typically not harmful to you or your baby. You may not even have any symptoms and not realize it's a bit low unless the doctor tells you at your prenatal visit.

Low blood pressure is only a concern if you have symptoms, or it's extremely low. Supine hypotension syndrome is a type of low blood pressure that could be dangerous. Compression of your major blood vessels can affect your heart rate and circulation. It can make you feel dizzy, faint, or sweaty and lead to severe complications that can harm both you and your baby.  

You can prevent supine hypotension and the problems it causes by not lying flat on your back, especially after the fifth month. Try using pillows or a wedge to sleep tilted toward or on your left side and avoid exercising on your back. If you want more information about supine hypotension or if you have any symptoms or questions about your blood pressure, be sure to talk to your doctor.