Supine position in pregnancy – dangerous or not?

Whether certain foods, sports, or even hanging laundry – the list of things that pregnant women are supposedly supposed to avoid is long. While some recommendations make sense, others seem rather questionable.

This multitude of dos and don'ts often leads to uncertainty and growing fears. Even when sleeping, many pregnant women wonder if they could be doing something wrong. However, we only have limited influence on our behavior while sleeping. But how does it actually come about that pregnant women even think about whether they are allowed to lie or sleep on t heir backs?

In the human body, blood flows through a vast network of blood vessels. One of the most important is the inferior vena cava. It runs along the right side of your spine and carries oxygen-poor blood from the lower half of your body back to the heart. 

As the baby grows, your uterus becomes heavier. If you lie flat on your back, the uterus presses with its full weight directly on this large vein—like stepping on a garden hose. The blood can no longer flow properly, less of it reaches the heart, and your blood pressure drops

• Sudden drop in blood pressure
• Dizziness or lightheadedness
• Rapid pulse (heart racing)
• Brief loss of consciousness (syncope)
• Nausea or vomiting
• Cold sweats
• Noticeable paleness

When and how strongly you notice these symptoms also depends on your individual physical constitution. Very petite women sometimes notice symptoms earlier — for example, in a semi-reclined position at the dentist or in a beauty salon. Gymnastic exercises performed while lying on the back are also no longer recommended after the 28th week of  pregnancy at the latest. As soon as discomfort occurs, changing position quickly is the right response.

The cause of vena cava compression syndrome is that the significantly enlarged and heavier uterus during pregnancy presses on the inferior vena cava. From about the 20th week of pregnancy, the uterus in the supine position can exert so much pressure on this large blood vessel that the blood supply to the heart is reduced. As a result, the cardiac output decreases, leading to a drop in blood pressure. This is manifested in the pregnant woman by a noticeable drop in blood pressure and a simultaneous increase in heart rate.

Vena cava compression syndrome can also occur outside of pregnancy, for example due to space-occupying lesions such as tumors  or in cases of extreme obesity.

Symptoms can also occur in the child, provided there is an acute hypoperfusion, i.e., reduced blood flow to the placenta. This can be detected, for example, during a CTG or while listening to the baby's heart sounds. A drop in heart sounds would then be visible or audible. After a change in the mother's position, however, the heart sounds usually normalize quickly. Since the symptoms described in the mother are usually very noticeable, she will instinctively lie down differently or sit up. The baby is therefore usually not exposed to this situation unnoticed.

This is exactly the reason why there are no blanket recommendations for resting positions, especially in the first months of pregnancy. If lying on your back feels comfortable and pleasant, you can continue to do so. Lying on your left side is best for the baby's circulation. This way, there is the least pressure on blood vessels and internal organs.

In the second half of pregnancy, it is recommended to rest and fall asleep on your side. However, pregnant women do not need to panic if they wake up lying on their back. If symptoms of vena cava compression syndrome do occur, they would usually cause the affected person to wake up on their own and change position.   

Lying on your back is not only an unfavorable position during birth, but also in late pregnancy, when the baby is slowly making its way to the birth canal and getting into the best possible starting position. With the right posture, you can support this process well. 

• A long nursing and positioning pillow supports your side position at night.  

• If your hair is longer, a tied hair bun at the back of your head can also be useful: If you turn onto your back while sleeping, the unfamiliar feeling will make it easier for you to wake up and change position. 

• Especially in the later stages of pregnancy, to prevent vena cava compression syndrome, make sure to lie on your side. This also applies to examinations such as CTG or ultrasound.  

• Even when positioning in preparation for a possible abdominal birth (cesarean section), lying completely on your back should be avoided or kept as short as possible.

Lying on your back during pregnancy should be approached with caution from the second half of pregnancy onward, especially for prolonged periods of resting or sleeping. Vena cava compression syndrome is a real phenomenon, but in most cases it can be resolved immediately by simply changing position. Those who pay attention to their body and prefer side-lying are on the safe side. 

As with all physical changes during pregnancy, it is important to pay close attention to your own sensations and respond accordingly. If a position becomes uncomfortable, don't be falsely polite and don't wait, for example, until the dentist has finished the treatment. Regularly check whether your posture is still comfortable, and don't hesitate to change it if necessary. This mindfulness is not only helpful in everyday life, but also good preparation for birth.