Most pregnant people can and should keep exercising, but modifications become necessary at specific points as your body changes. The short answer: some adjustments start as early as the first trimester, while others kick in around weeks 20 to 24. The goal at 150 minutes of moderate-intensity activity per week stays the same throughout pregnancy. What changes is how you get there.
The First Trimester: Fewer Changes Than You Think
If you were physically active before pregnancy, you can generally continue your existing routine through the first trimester with minimal changes. The U.S. Physical Activity Guidelines specifically note that people who habitually engaged in vigorous-intensity exercise before pregnancy can continue those activities during pregnancy. That includes running, weightlifting, cycling, and group fitness classes.
The main first-trimester adjustments are practical rather than structural. Fatigue and nausea may force you to shorten sessions or swap morning workouts for afternoon ones. This is also a good time to start paying attention to how hard you’re working using perceived exertion rather than heart rate. Pregnancy changes how your cardiovascular system responds to exercise, so your heart rate becomes a less reliable gauge of intensity. If you can hold a conversation but not sing, you’re in a good range for moderate effort.
Why Your Joints Need Extra Attention Early On
One change that begins in the first trimester, well before your belly grows, is hormonal. Your body starts producing relaxin, a hormone that loosens ligaments to prepare your pelvis for delivery. Relaxin doesn’t just affect the pelvis. It acts on connective tissue throughout your body, breaking down collagen fibers and reducing ligament integrity in joints like the knees, ankles, and hips.
Research on elite female athletes found that those with higher relaxin levels had more than four times the risk of an ACL tear compared to athletes with lower levels. You don’t need to stop exercising because of this, but it does mean certain movements deserve more caution from early pregnancy onward:
- Heavy single-leg exercises like pistol squats or deep lunges, which place high stress on the knee
- Explosive lateral movements like tennis, basketball, or agility drills
- Maximal lifts that push joints to end range under load
Switching to controlled, bilateral movements (squats instead of Bulgarian split squats, for instance) and reducing loads by 10 to 20 percent gives your joints a wider safety margin without sacrificing the training stimulus.
The 20-to-24-Week Turning Point
The second trimester brings the most visible shift in what your workouts should look like, and the biggest single change happens between weeks 20 and 24. This is when your uterus grows large enough to compress a major blood vessel, the inferior vena cava, when you lie flat on your back. That compression reduces blood flow returning to your heart and can cause dizziness, nausea, and a drop in blood pressure.
After 24 weeks, avoid exercises performed flat on your back. That rules out standard bench presses, floor-based crunches, supine hip bridges, and any yoga pose that keeps you supine for more than a few seconds. If you experience symptoms even before 24 weeks, make the switch earlier. The fix is simple: incline your bench to at least 30 degrees, or position a wedge under your left hip to tilt your pelvis. Symptoms resolve quickly once you shift off your back.
This is also the period when your center of gravity begins shifting forward noticeably. Running on uneven terrain, trail hiking, and exercises that challenge your balance (box jumps, single-leg deadlifts) carry a higher fall risk. Moving runs to flat surfaces or a treadmill, and choosing seated or supported versions of balance-heavy exercises, keeps you moving without the added danger.
Third Trimester: Scaling Down Impact and Intensity
By the third trimester, the combination of a larger belly, looser joints, and increased blood volume means high-impact activities become uncomfortable or impractical for most people. This is the natural point to transition running to brisk walking, swap jumping movements for step-ups, and shift from barbell exercises to dumbbells or machines that allow a more comfortable range of motion around your belly.
The 150-minute weekly target still applies. Walking, swimming, stationary cycling, and prenatal yoga are all effective ways to hit it. Swimming is especially useful in the third trimester because buoyancy supports your joints and helps manage swelling.
None of this means you must stop strength training. You can continue lifting weights through the third trimester as long as you make two key adjustments: reduce the load enough that you never need to hold your breath to complete a rep, and exhale steadily through the hardest part of each lift. Holding your breath and bearing down (the Valsalva maneuver) spikes pressure in your abdomen and reduces blood flow to the placenta. Breathing with an open mouth during exertion, sometimes called open glottis breathing, avoids that pressure spike entirely.
Pelvic Floor Signals You Shouldn’t Ignore
Your pelvic floor bears increasing load as pregnancy progresses, and it will tell you when your current workout is too much. The clearest signal is urinary leaking during exercise, whether during a jump, a sneeze mid-set, or a heavy squat. Any involuntary loss of urine during physical exertion is stress urinary incontinence, and it’s common in pregnancy, but it’s also a sign that the demand on your pelvic floor exceeds its current capacity.
If you notice leaking, heaviness, or a dragging sensation in your pelvis during or after workouts, reduce the impact level or the weight you’re lifting. Drop box jumps for step-ups. Lighten your squat. Shorten your run. These symptoms don’t mean you need to stop exercising entirely, but they do mean your current intensity needs to come down a notch. Pelvic floor muscle training (Kegels done correctly) can help build capacity, though working with a pelvic floor physiotherapist gives you more targeted guidance than guessing on your own.
Keeping Your Temperature in Check
Pregnancy impairs your body’s ability to cool itself efficiently, and your core temperature should not exceed 102°F (roughly 39°C). Overheating is dangerous for both you and the baby. This matters most during outdoor exercise in hot or humid conditions, but it also applies to hot yoga, heated fitness studios, and overdressing during winter workouts.
Practical steps: exercise during cooler parts of the day, stay well hydrated, wear breathable clothing, and move indoors when the heat index is high. If you feel excessively sweaty, dizzy, fatigued, or develop muscle cramps or unquenchable thirst, stop immediately, get to a cool environment, and use cool cloths to bring your temperature down.
Signs to Stop a Workout Immediately
Certain symptoms during exercise are red flags regardless of trimester. Stop your workout and contact your provider if you experience vaginal bleeding, fluid leaking from the vagina, regular painful contractions, dizziness or feeling faint that doesn’t resolve with rest, chest pain, calf pain or swelling, or sudden shortness of breath before you’ve started exerting yourself. These may signal complications that require evaluation before you return to exercise.
For people with obstetric complications like placenta previa, preeclampsia, or cervical insufficiency, exercise recommendations need to be individualized. A few maternal medical conditions make aerobic exercise off-limits entirely, but they are rare. If you have any complicating condition, get specific clearance and guidance rather than following general recommendations.