Maternal health specialists have strongly advised pregnant women to avoid lying on their backs after the first trimester, warning that doing so can dangerously reduce blood flow to essential organs. Gynaecologists emphasized that the back-sleeping position can compress major veins, resulting in serious health risks for both mother and baby.
Why Back Sleeping Becomes Risky During Pregnancy
Medical experts explained that sleeping on the back during the second and third trimesters can lead to a dangerous condition where the growing womb puts pressure on the large veins along the spine. This pressure may restrict blood flow back to the heart and brain, which in turn reduces oxygen delivery throughout the body.
According to them, lying flat on the back may result in fainting, dizziness, excessive sweating, and even vomiting. Prolonged back sleeping could even become fatal if blood circulation is severely compromised. In contrast, they highlighted the left side as the most recommended sleep position, as it prevents uterine pressure on blood vessels and promotes better blood circulation.
Expert Explanation: How Sleep Position Affects Circulation
Speaking in an interview with Frontpage Health, Dr. Uche Agu, an Associate Professor and Consultant Obstetrician and Gynaecologist at the University of Nigeria Teaching Hospital, explained the dangers associated with the back-sleeping position during pregnancy.
“When a woman is pregnant, her sleeping position becomes crucial because of how close the major blood vessels are to the spine,” he said. “The vein that returns blood to the heart and brain is positioned directly along the spine. As the uterus grows, lying on the back causes the womb to press on these veins.”
Dr. Agu further stated that the vein responsible for returning blood to the heart and brain is collapsible and more susceptible to compression than arteries. When compressed, it drastically reduces blood flow to the brain and heart, which can cause fainting and other complications.
What Happens When Veins Collapse During Pregnancy
“When a pregnant woman lies on her back,” Dr. Agu continued, “the enlarged womb places pressure on these veins, causing them to collapse. This prevents adequate blood from reaching the heart and brain. The woman will begin to feel dizzy, sweaty, nauseous, and may even faint. In extreme cases, this can be life-threatening.”
He added that while the arteries continue to pump blood out, the veins’ inability to return blood means reduced oxygen supply to vital organs. Fortunately, the condition typically doesn’t persist because the discomfort usually causes women to change positions instinctively.
Why the Left Side is the Best Sleeping Position
Dr. Agu emphasized that the left side, medically known as the “left lateral position,” is the best choice for pregnant women. “When the woman lies on her left side, the pressure is taken off the major veins, allowing blood to flow freely. This position ensures both mother and baby receive adequate blood and oxygen.”
While sleeping on the right side is not as dangerous as lying flat on the back, he said it’s less ideal than the left due to potential pressure on internal organs. He urged women to prioritize left-side sleeping, especially during the second and third trimesters.
“We discourage sleeping face-up entirely,” he warned. “It is an uncomfortable and risky position during late pregnancy.”
Another Expert Weighs In
Supporting this advice, Dr. Philips Ekpe, a Consultant Obstetrician and Gynaecologist and former Secretary-General of the Nigerian Medical Association, explained that sleep position becomes more important as the baby grows heavier.
“In the first trimester, the baby weighs very little and doesn’t exert much pressure,” Dr. Ekpe said. “But by the second and third trimesters, the uterus and the baby become significantly heavier. Lying on the back at that point allows the entire weight to press directly on the veins running along the spine.”
He clarified that these veins are responsible for transporting blood to critical organs like the brain, kidneys, heart, lungs, and the baby itself. Compression of these veins can reduce blood supply to these organs and increase the risk of complications, including stillbirth and maternal collapse.
Risks of Sleeping on the Back: Stillbirth, Preeclampsia, and More
Medical studies have linked back-sleeping and even right-side sleeping to an increased risk of stillbirth, restricted fetal growth, low birth weight, and preeclampsia—a severe pregnancy complication characterized by dangerously high blood pressure.
Health professionals recommend the left-side position not just to avoid maternal fainting but also to optimize oxygen and nutrient delivery to the fetus. Improved circulation also helps maintain kidney and liver function, which are essential for filtering toxins and maintaining fluid balance during pregnancy.
Research Backs the Experts
According to MedicalNewsToday, many pregnant women find it challenging to sleep comfortably during the later stages of pregnancy. A National Sleep Foundation survey found that 78% of pregnant women struggle with sleep quality, with 15% experiencing restless leg syndrome during the third trimester.
The online health portal reiterated that the left-side sleeping position is most beneficial during the second and third trimesters. It helps keep the uterus from compressing the inferior vena cava—the major vein that returns blood from the lower body to the heart.
Final Recommendations for Pregnant Women
Both Dr. Agu and Dr. Ekpe urged women to start training themselves to sleep on their left side early in pregnancy, even if the baby bump is still small. Developing the habit early can make it easier to maintain safe sleep positions later in pregnancy when the risks increase significantly.
“Women should understand that their sleep position directly affects their well-being and that of their baby,” Dr. Agu concluded. “By sleeping on the left side, they can prevent avoidable complications and support healthy pregnancy outcomes.”
In summary, maternal health experts strongly advise pregnant women—especially those in their second and third trimesters—to avoid sleeping on their backs. Instead, they recommend the left-side position to enhance blood flow, prevent maternal fainting, and reduce the risk of serious complications like stillbirth or preeclampsia.
