Sleeping on your left side is generally recommended during pregnancy to maximize blood flow to the uterus and fetus, especially after 28 weeks.
If you have spent years happily sleeping on your back or stomach, hearing that you need to switch sides during pregnancy can feel like one more thing to worry about. Add in the conflicting advice from friends or online forums, and it is easy to feel uncertain about what your body actually needs at night.
The honest answer is that experts widely recommend side sleeping throughout the second and third trimesters, with your left side offering the best combination of circulation and comfort. This does not mean you will stay perfectly on your left side all night long—most people shift in their sleep. What matters is that you make a conscious effort to start on your side and use pillows to help make the position more sustainable.
Why Left-Side Sleeping Tops the List During Pregnancy
The recommendation to sleep on your left side has a specific anatomical basis. A major vein called the inferior vena cava (IVC) runs along the right side of your spine and carries deoxygenated blood from your lower body back to your heart.
As your uterus grows, especially after the 20-week mark, lying flat on your back can place the full weight of your uterus directly onto the IVC. That pressure can reduce blood flow returning to your heart, which may lower cardiac output and affect oxygen delivery to the placenta.
Sleeping on your left side shifts your uterus away from the IVC, allowing blood to flow freely. This positioning also gives your liver optimal space and tends to improve kidney function, helping your body manage the increased fluid load of pregnancy.
When Your Sleep Position Actually Starts to Matter
The timeline for prioritizing side sleeping can feel a little vague. Here is what the research suggests for each stage of pregnancy so you can plan accordingly.
- First Trimester (Weeks 1–13): Sleeping on your back, side, or stomach is generally all considered acceptable. Your uterus is still small and nestled behind the pubic bone, so it is unlikely to compress the IVC.
- Second Trimester (Weeks 14–27): This is a good window to start practicing side sleeping. By week 20, your uterus is large enough that back sleeping may begin to trigger dizziness, shortness of breath, or lower back pain for some people.
- Third Trimester (Weeks 28–40): Side sleeping becomes the strongly recommended position during this stage. Left-side sleeping has been associated with the lowest risk of stillbirth compared to back or right-side sleeping in some large studies.
- What About Right-Side Sleeping?: While left is often considered the gold standard, right-side sleeping is generally considered a safe alternative. The evidence is less clear for right-side sleeping, but it is still vastly preferable to lying flat on your back.
- Waking Up on Your Back: If you wake up on your back, simply roll back to your side. Your body will usually let you know if something is off through discomfort or a feeling of breathlessness.
The exact timing varies, but most healthcare providers suggest making a deliberate shift to side sleeping from around 28 weeks onward. Practicing earlier can make the transition feel much more natural.
What the Research Says About Sleep Position
A 2019 study from the National Institutes of Health looked at sleep position in late pregnancy and found notable differences in outcomes. The data suggested that women who slept on their back or right side had a higher likelihood of stillbirth compared to those who slept on their left.
This led the NICHD to highlight the importance of positioning. Their public guidance encourages expecting parents to sleep on their left side during the third trimester, calling it the “gold standard” posture for maximizing placental blood flow.
The mechanism many clinicians point to involves the supine position’s effect on cardiac output. When the IVC is compressed, less blood reaches the heart, which means less oxygenated blood circulates to the placenta. Avoiding prolonged back sleeping is a straightforward way to help maintain steady circulation during the later stages of pregnancy.
| Sleep Position | Blood Flow Impact | General Recommendation |
|---|---|---|
| Left Side | Maximizes IVC blood flow, optimal placental perfusion | Generally considered the best option in 2nd/3rd trimester |
| Right Side | Slightly less optimal than left, but still good | Considered a safe alternative |
| Back (Supine) | Can compress IVC, reducing cardiac output | Not recommended after ~20 weeks |
| Stomach (Prone) | Becomes uncomfortable as belly grows | Safe in early pregnancy, impractical later |
| Reclined (Semi-supine) | Less pressure on IVC than flat back | Some find this a helpful transition position |
These comparison points help explain why doctors emphasize side sleeping over other positions, but they also underscore that you have room to adjust if left-side sleeping is challenging for your hips or shoulders.
Practical Tips to Make Side Sleeping Work
Switching to side sleeping can be surprisingly uncomfortable if you are used to a different position. Your hips and shoulders may ache, and a growing belly can make the position feel unstable. A few simple adjustments can make side sleeping much easier to maintain.
- Use a Pregnancy Pillow: A full-length body pillow can support your belly and back simultaneously, creating a sleep “nest” that helps you stay on your side without rolling over.
- Place a Pillow Between Your Knees: This simple trick aligns your hips and reduces lower back strain, which is a common source of discomfort during side sleeping.
- Tuck a Small Pillow Under Your Belly: A small, soft pillow or rolled blanket under your bump provides gentle support and reduces the pulling sensation on your abdominal muscles.
- Try the “SOS” Position (Sleep on Side): If you wake on your back, try placing a pillow behind your back to prevent yourself from fully rolling flat. This acts as a physical barrier.
Comfort is a key part of the equation. If you are in pain, you will not sleep well regardless of your position. Experiment with different pillow setups to find what works for your particular body and growing bump.
How to Transition If You Are a Dedicated Back or Stomach Sleeper
If side sleeping feels impossible right now, you are not alone. Many people struggle to break a lifelong sleep habit. The good news is that you can train your body to prefer side sleeping over time with consistent practice.
Per the 28 weeks pregnancy guide from Healthline, side sleeping is the primary recommendation during the third trimester. If you are reading this before week 28, you have a good window to practice and get comfortable with the new position.
Start by going to sleep on your left side, even if you know you will move during the night. Falling asleep in the correct position sets a helpful baseline. You can also use the “pillow fort” method—piling pillows around your back so that rolling over requires enough effort to wake you up. Over time, side sleeping will start to feel like your natural default.
| Barrier | Quick Fix |
|---|---|
| Hip or shoulder pain | Try a thicker mattress topper or a pillow between the knees for alignment |
| Waking up on your back | Tuck a firm pillow behind your back to prevent rolling completely flat |
| General discomfort | Place a small pillow or rolled blanket under your bump for gentle support |
The Bottom Line
Side sleeping, particularly on your left, is widely recommended during the second and third trimesters to support healthy blood flow to the uterus and fetus. While right-side sleeping is also considered a reasonable option, back sleeping should ideally be avoided once you reach the 20-week mark. Pillows and consistent practice can help make the transition more comfortable.
Your obstetrician or midwife can review your specific pregnancy history and help you plan a sleep setup that works for your body and your baby’s needs, especially if you have a high-risk condition like preeclampsia or a multiple pregnancy.
References & Sources
- NICHD. “Pregnancy Sleep Position” Many physicians advise pregnant women to sleep on their left side.
- Healthline. “Sleeping Positions in Pregnancy” It is typically recommended to sleep on your side from 28 weeks of pregnancy onward.