The third trimester brings a new set of physical limitations and safety considerations that didn’t apply earlier in pregnancy. Your uterus is now large enough to compress major blood vessels, your center of gravity has shifted, and your baby is developing rapidly in ways that make certain medications, activities, and environmental exposures riskier than before. Here’s what to skip or modify from week 28 onward.
Sleeping Flat on Your Back
By about 20 weeks, your uterus is heavy enough to press on the inferior vena cava, the large vein that returns blood to your heart, when you lie flat on your back. In the third trimester, this compression is significant. Less blood returning to your heart means less blood flowing to you and to your baby. One study found a potential increased risk of stillbirth among people who slept on their backs the entire night.
Side sleeping is the fix, and either side works. The left side is considered slightly ideal because of how your blood vessels are positioned, but right-side sleeping still provides good blood flow. If you wake up on your back in the middle of the night, don’t panic. Simply roll to your side. A pillow wedged behind your back can help keep you from rolling over while you sleep.
Taking Common Pain Relievers
Ibuprofen, naproxen, and aspirin belong to a class of painkillers called NSAIDs, and the FDA recommends avoiding all of them from 20 weeks of pregnancy onward. They can reduce amniotic fluid levels, which your baby needs for lung and limb development. At around 30 weeks, the risk escalates: NSAIDs can cause premature closure of a blood vessel in the baby’s heart called the ductus arteriosus, which is supposed to stay open until birth. This can lead to serious heart and lung problems in the newborn. If you need pain relief in the third trimester, talk to your provider about safer alternatives.
High-Impact and High-Risk Activities
Exercise itself is beneficial throughout pregnancy, but the types of movement that are safe narrow considerably in the third trimester. Your shifted center of gravity makes balance-dependent activities genuinely dangerous, and any blow to the abdomen carries serious risk.
Activities to stop entirely include:
- Contact sports like soccer, basketball, ice hockey, and boxing
- Fall-prone activities like downhill skiing, water skiing, surfing, horseback riding, off-road cycling, and gymnastics
- Extreme environments like scuba diving, skydiving, and anything above 6,000 feet if you don’t already live at altitude
When you do exercise, avoid jerky or bouncy movements and don’t stand motionless for long stretches, which can cause blood to pool in your legs and drop your blood pressure. A good intensity check: you should be able to talk normally but not sing. If you can’t hold a conversation, dial it back.
Heavy Lifting Without Precautions
A common guideline is to avoid lifting more than 20 pounds during pregnancy, though the actual risk depends on your fitness level, how often you’re lifting, and whether you have existing back issues. There isn’t strong data linking a single heavy lift to complications, but repetitive bending and lifting can strain your loosened joints and pelvic floor, both of which are already under pressure from the weight of your uterus. If your job or daily life involves frequent lifting (a toddler, groceries, work equipment), use your legs rather than your back, hold objects close to your body, and ask for help when something feels like too much.
Hot Tubs, Saunas, and Overheating
Anything designed to raise your core body temperature is off-limits throughout pregnancy, and especially in the third trimester when you’re already running warmer. Hot tubs, saunas, steam rooms, and hot yoga all pose risks to fetal development by driving your internal temperature too high.
Warm baths are fine as long as the water stays at or below 99°F (37°C), which feels comfortably warm but not hot. A good rule: if the water makes your skin turn red or you start to sweat, it’s too hot. A bath thermometer is a cheap way to check.
Cleaning With Harsh Chemicals
Strong fumes from household cleaners, pesticides, and paint can be harmful during pregnancy. In the third trimester, you may be nesting and tempted to deep-clean everything, but avoid inhaling concentrated chemical fumes. If you must use conventional cleaners, wear gloves, open windows, and don’t lean over the product while it’s working. Better yet, switch to chemical-free alternatives for the remaining weeks. Vinegar, baking soda, and unscented castile soap handle most household cleaning tasks without the fume exposure.
Flying Too Late in Pregnancy
Most commercial airlines allow pregnant passengers to fly up to 36 weeks of gestation, but the cutoff varies. Some carriers restrict international flights earlier, and many require a letter from your provider confirming your due date. If you’re planning third-trimester travel, check with your specific airline before booking. Beyond airline policies, long flights increase the risk of blood clots, which is already elevated in pregnancy. Staying hydrated, wearing compression stockings, and getting up to walk the aisle every hour or two can help.
Ignoring Changes in Movement or Symptoms
The third trimester is when you should be paying close attention to your baby’s movement patterns. While there’s no single universal standard, most providers will ask you to track kick counts. The general approach: pick a time when your baby is typically active, and note how long it takes to feel a set number of movements. Your provider will give you specific instructions. What matters most is noticing a change from your baby’s normal pattern. A baby who was active and suddenly goes quiet warrants a call.
Certain symptoms in the third trimester need immediate attention because they can signal preeclampsia, a dangerous blood pressure condition that develops after 20 weeks. Watch for a headache that won’t go away, blurred vision or seeing spots, sudden swelling in your face and hands (not just feet, which often swell normally), pain in your upper right abdomen, and trouble breathing. Preeclampsia is diagnosed when blood pressure reaches 140/90 or higher, but you won’t always know your numbers between appointments. The symptoms above are your early warning system, and they can escalate to seizures or organ damage if untreated.
Standing Still for Long Periods
This one surprises people, but prolonged standing without movement can cause blood to pool in your lower legs when you’re in the third trimester. The weight of your uterus already compresses your blood vessels, and gravity working against sluggish return flow can make you lightheaded or cause your blood pressure to drop suddenly. If your job or daily routine requires standing, shift your weight between feet, take short walking breaks every 20 to 30 minutes, and sit when you can. Compression socks help here too, keeping blood moving back toward your heart instead of settling in your ankles.