During pregnancy, certain body positions can compress major blood vessels, reduce blood flow to your baby, or strain your changing body. The most important position to avoid is lying flat on your back, especially after 30 weeks. But several other positions during sleep, exercise, work, and daily life also deserve attention as your pregnancy progresses.
Why Lying on Your Back Is the Main Concern
The core issue is a large vein called the inferior vena cava that runs along the right side of your spine. This vein carries blood from your lower body back to your heart. When you lie flat on your back, the weight of your growing uterus presses directly on it, restricting blood flow back to your heart and out to the placenta.
This matters more than you might expect. Blood flow to the uterus increases tenfold during pregnancy, from about 60 milliliters per minute to 600 milliliters per minute at full term. Because of that massive increase, even a modest drop in blood return can have outsized effects on both your circulation and your baby’s oxygen supply. When compression is significant, it can cause dizziness, nausea, a sudden drop in blood pressure, sweating, and a racing heart. This is sometimes called supine hypotensive syndrome, and it’s your body’s signal to change position immediately.
When Back Sleeping Becomes Risky
An NIH-funded study found that sleeping on your back or side through the 30th week of pregnancy does not appear to increase the risk of stillbirth, reduced birth size, or high blood pressure complications. Among more than 400 women who slept on their back over half the time during early and mid-pregnancy, outcomes were no worse than for those who favored other positions. So if you wake up on your back at 24 weeks, there’s no reason to panic.
After 30 weeks, the picture changes. A meta-analysis of five studies covering over 3,000 pregnancies found that going to sleep in the supine position in late pregnancy was associated with 2.6 times the risk of stillbirth compared to falling asleep on the left side. Researchers estimated that roughly 6% of late-term stillbirths may be attributable to the supine sleep position. Notably, going to sleep on the right side did not show the same increased risk. The key takeaway: the position you fall asleep in matters most, since that’s the position you spend the longest stretch in.
Best Sleep Position After 30 Weeks
Sleeping on your left side is widely recommended because it allows the most blood flow to your baby and improves kidney function, helping your body filter waste and reduce swelling. That said, sleeping on your right side is also considered safe. The goal is simply to avoid falling asleep flat on your back.
A pillow between your knees can keep your hips aligned and take pressure off your lower back. Some women tuck a pillow behind their back as a physical reminder not to roll over. If you do wake up on your back, just roll to your side. Your body will often wake you before any real harm is done, precisely because the drop in blood pressure triggers discomfort.
Positions to Avoid During Exercise
The same vena cava compression that makes back sleeping risky also applies to exercise. After the first trimester, avoid spending extended time in any exercise position that has you lying face-up. This rules out a number of common moves: crunches, bench presses, bridges held for long periods, and many floor stretches done on your back.
If you practice yoga, several categories of poses become problematic as pregnancy progresses:
- Belly-down poses like cobra, locust, bow, and sphinx should be dropped after the first trimester for the obvious reason that they press against your abdomen.
- Back-lying poses like corpse pose, happy baby, and reclined twists put pressure on the vena cava during the second and third trimesters.
- Closed twists and forward folds with your legs together compress the abdomen and restrict blood flow. Open twists (twisting away from the forward knee rather than into it) are a safer alternative.
- Full inversions like headstands, handstands, and shoulderstands are risky because the added weight of the baby, placenta, and amniotic fluid puts pressure on your diaphragm and heart when you’re upside down. The balance challenges alone make falls more likely.
Modified versions exist for nearly all of these. Corpse pose can be done on your left side. Forward folds can be widened to make room for your belly. A prenatal yoga class will already have these substitutions built in.
Standing Too Long in One Position
Prolonged standing is its own kind of problematic position. The CDC recommends that pregnant workers reduce or avoid standing for three hours or more at a stretch, as it may increase the chance of preterm birth. The concern is that gravity pools blood in your legs, reducing the volume returning to your heart, much like lying on your back does through compression.
Standing with your weight shifted onto one leg is particularly worth avoiding. Pregnancy hormones loosen the ligaments around your pelvis, and the joints on either side of your sacrum (at the base of your spine) can develop uneven laxity. Women with pregnancy-related pelvic girdle pain already have reduced ability to stabilize the pelvis, and asymmetric standing makes this worse, changing your gait and balance in ways that can become painful. If your job requires long periods on your feet, shifting positions frequently, using a footrest to alternate legs, and taking seated breaks all help.
Lifting and Twisting Positions
Lifting while twisting your torso is a recognized risk factor for overexertion injury in anyone, but pregnancy raises the stakes. Your center of gravity has shifted forward, your abdominal muscles are stretched and less able to brace your spine, and the relaxin circulating in your body makes your joints less stable. Clinical guidelines for occupational lifting in pregnancy note that recommended weight limits drop significantly when the lift involves spinal rotation, stooping, or reaching forward rather than keeping the load close to your body.
The practical rule: face whatever you’re picking up directly, bend at the knees rather than the waist, and hold the object close to your chest. Avoid reaching overhead while holding anything heavy, and never twist to set something down. Turn your whole body by moving your feet instead.
Sitting Positions That Cause Problems
Sitting cross-legged for long periods or in deep squatting positions may aggravate pelvic pain if you’re already experiencing symphysis pubis discomfort. Slouching in a chair pushes your pelvis into a tucked position that increases pressure on your lower back, which is already under strain from the forward pull of your belly.
When sitting for extended stretches, keep your feet flat on the floor with your knees at roughly hip height. A small cushion or rolled towel behind your lower back helps maintain the natural curve of your spine. Getting up and moving every 30 to 60 minutes prevents blood from pooling in your legs and keeps your joints from stiffening.