Both medical research and clinical observations in labor and delivery demonstrate that left side sleep during pregnancy is best.
If you have always been a left-sided sleeper you are one of the fortunate ones. Left side sleep during pregnancy has been shown to be beneficial in both pregnant and non-pregnant individuals.
Left side sleep during pregnancy not only improves placental blood flow to the fetus, it also enhances maternal circulation, improving lymphatic drainage and gastric emptying. This is important since hormones slow gastric emptying during pregnancy.
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Sleeping on your left side is a simple lifestyle change and the benefits are very real.
This article will focus on left side sleep during pregnancy and why health care providers, especially during pregnancy, advise
lying or sleeping on your left side. Lastly, we will discuss why lying on your left side is the overall best sleeping position for men
and women who have no physical or medical restrictions.
Why left side sleep during pregnancy is best!
To understand why left side sleep during pregnancy is the best sleeping position, it is important to review the anatomy of the large vein called the vena cava which courses down your back.
This vein is easily compressed by the weight of your baby bump if you lie on your right side.
This vena cava runs adjacent to the aorta and is responsible for returning blood to the maternal heart. This large vessel runs alongside the spine and is compressed when lying on one’s left side.
Since the venous system is a low-pressure system, it is easily affected by compression through the vessel is affected by the weight of the pregnant uterus, particularly when lying flat on one’s back.
The size and weight of the baby bump in the third trimester is why left-sided
The venous system is a low-pressure system, allowing veins to easily be compressed or obstructed by the external pressure from adjacent organs.
It should be no surprise, based on this understanding, why a tourniquet can obstruct blood flow in veins, whereas a high-pressure blood pressure cuff is required to obstruct arterial blood flow.
Furthermore, the fact that the vena cava travels down the right side of the spinal cord is the reason why left side sleep during pregnancy is best to optimize perfusion through the vena cava and allow the optimal flow of blood back to the heart and ultimately to the growing fetus.
Is there clinical proof that sleeping on your left side can be beneficial?
There is very clear clinical proof that left-sided positioning during pregnancy improves blood circulation to the fetus through the uteroplacental circulation.
We know blood flow to the placenta is decreased by the weight of the pregnancy on the vena cava* based on research and clinical observations made during fetal heart rate monitoring:
Research: From a research standpoint, studies have shown that blood flowing back to the heart in pregnant and non-pregnant individuals does improve when sleeping on your left side.
Clinical Observations: Observations during fetal heart rate monitoring clearly demonstrate the benefit of left-sided maternal positioning. Any prenatal care provider can relate to what I am going to discuss as this is a common observation and maneuver we all have used to improve fetal-placental blood flow.
The vena cava is the large vein that travels down your back adjacent to the aorta and spine. This blood vessel returns blood to the heart. The blood pressure in the Vena Cava is low, so it can be compressed when pressure is put on it by adjacent structures.
It is not uncommon for a health care provider (doctor/midwife/nurse) to observe a drop in the fetal heart rate during fetal heart rate monitoring.
When this occurs, immediate maternal positioning on the left side will most often allow the fetal heart rate to recover.
This is the result of facilitating increased blood flow to the fetal-placental circulation, by taking the obstructive weight of the pregnant uterus off the vena cava.
This maneuver will often be all that is necessary to allow the fetal heart rate to return to a normal.
If this management does not improve the situation, there may be other factors contributing to impaired placental perfusion and further management decisions will be required immediately based on the clinical situation.
The illustration below is a fetal heart rate tracing with a fetal heart rate deceleration responding to left-sided maternal
positioning. It is an objective demonstration of how the fetal heart rate is affected by vena cava compression and how sleeping
on the left side allows optimal fetal-placental perfusion.
Illustration of FHR deceleration responding to left-sided maternal positioning
So why is left side sleep during pregnancy best?
The answer is simple and can make one wonder why this advice is not discussed with all prenatal patients. Unfortunately, the
only time this topic usually comes up is when there are BP concerns, fetal growth concerns or during active labor when there
are changes in the fetal heart rate tracing. This article is simply intended to show why left-sided sleep during pregnancy is
beneficial. If you are reading this, hopefully, you will find it helpful. Perhaps the day will come when left-sided bedrest is
during one’s prenatal care. There are clinical reasons why left-sided maternal positioning helps manage elevated blood pressure
relating to pregnancy. Again this is not just a theoretical benefit as blood pressure clearly can be clinically shown to decrease
when a woman with hypertension related to pregnancy lies on her left side. Any woman reading this article who has or had high
blood pressure during pregnancy (toxemia/preeclampsia) knows how important left side sleep during pregnancy can be.
Two more benefits of left side sleep during pregnancy.
It is important to note two other benefits from lying on one’s left side:
- Stomach: Improves gastric emptying which can reduce heartburn
- Lymphatic System: improves lymphatic drainage
A pregnancy pillow might be just what you need!
If you find it difficult to sleep on your left side, use a pregnancy pillow. The comfort alone will leave you wondering how you
ever got along without one! Pregnancy pillows offer a number of benefits. They can relieve the pregnancy-related discomfort
many pregnant women experience in their lower back and pelvis. It also can be therapeutic for musculoskeletal conditions that
may have been present prior to pregnancy such as sciatica and chronic low back pain. The illustration below shows how a
pregnancy pillow can help maintain alignment of the neck, spine, pelvis and lower extremities.
For more information about sleep during pregnancy, check out some of our other articles:
Lying flat on your back during pregnancy should always be avoided to provide optimal blood flow to the placenta. Lying on
either side is better than lying on your back. During the later stages of pregnancy, many women will feel dizzy when they lie on
The information shared in this article is intended to demonstrate why sleeping on your left side can be beneficial.
Unfortunately, left side sleep during pregnancy is only discussed if there is a medical complication that would benefit from left
side sleep during pregnancy (ie. fetal growth concerns, high blood pressure).