Most exercise is safe and encouraged during the first trimester, but a handful of activities carry real risks and should be skipped entirely. The American College of Obstetricians and Gynecologists recommends at least 150 minutes of moderate-intensity aerobic activity per week throughout pregnancy, and women who were already active before conceiving can generally keep up their routines. The key is knowing which specific activities cross the line from beneficial to dangerous.
Contact Sports and Fall-Risk Activities
Any sport that puts you at risk of getting hit in the abdomen is off the table for the entire pregnancy, including the first trimester. That means ice hockey, boxing, soccer, and basketball. Even though your uterus is still tucked behind the pelvic bone early on, a direct blow can cause serious complications, and these risks only grow as pregnancy progresses.
Activities with a high chance of falling are also on the avoid list: downhill skiing, water skiing, surfing, off-road cycling, gymnastics, and horseback riding. Your body is already working against you here. A hormone called relaxin begins loosening your muscles, joints, and ligaments early in pregnancy to help your body accommodate a growing baby. That loosening effect can make you less stable on your feet and more prone to sprains and falls, even if you felt perfectly coordinated doing these activities before.
Hot Yoga and Heated Workouts
This is one of the most important categories to avoid in the first trimester specifically. Overheating during the early weeks of pregnancy, when the baby’s neural tube is forming, poses a measurable risk. A systematic review published through the Motherisk program found that women who experienced elevated core body temperature in the first trimester had roughly double the risk of neural tube defects in their babies. Separate research found that women who used hot tubs more than once during the first trimester had increased odds of certain birth defects, including anencephaly and gastroschisis.
Hot yoga classes typically take place in rooms heated to 35°C to 40°C (95°F to 104°F), which can push your core temperature into a risky range. Blood pressure also tends to run lower in the first trimester because progesterone relaxes blood vessel walls, so exercising in extreme heat makes dizziness and fainting more likely. Regular yoga in a normal-temperature room is fine and even beneficial. It’s the heated environment that creates the danger.
The same logic applies to saunas and hot tubs after a workout. ACOG specifically advises pregnant women to avoid high heat and humidity during exercise, with extra emphasis on heat stress prevention during the first trimester.
Scuba Diving
Scuba diving is contraindicated throughout pregnancy, including the very earliest weeks. The concern is decompression illness in the fetus. When you ascend from a dive, dissolved gases form bubbles in your bloodstream that your lungs filter out. A developing baby doesn’t have that filtering capacity, and animal studies suggest this can cause harm. Human data on the topic is limited and doesn’t definitively prove damage, but the quality of that data is too poor to rule it out either. Medical guidelines consistently recommend avoiding diving for the entire pregnancy. If you dove before realizing you were pregnant, that’s not considered a reason to panic, but it is a reason to stop.
Heavy Lifting and High-Pressure Core Work
You don’t need to abandon strength training in the first trimester, but certain movements deserve a closer look. Exercises that create a lot of intra-abdominal pressure, like heavy deadlifts, barbell squats at high loads, or maximal-effort lifts, can strain the connective tissue running down the center of your abdomen. Over time, this contributes to diastasis recti, a separation of the abdominal muscles that becomes harder to manage later in pregnancy and postpartum.
Planks and standard crunches are usually fine in the first trimester, but watch for “coning,” a visible ridge or bulge that pops up along the midline of your stomach during the movement. If you see it, that exercise is generating too much pressure for your body right now, and you should stop and switch to a modification. This is a signal worth paying attention to even early on, before your belly has grown noticeably.
Because relaxin is already loosening your joints, heavy lifting also raises your injury risk. Ligaments that normally stabilize your knees, hips, and spine are more lax than usual, so the same weight you handled comfortably before pregnancy may now put you closer to a strain or sprain. Reducing loads and focusing on controlled movements is a practical adjustment.
High-Altitude Exercise
If you’re not accustomed to exercising at elevation, keep your workouts below 2,500 meters (about 8,250 feet) for at least the first four to five days at altitude. The thinner air reduces oxygen availability, and your body needs time to compensate. For someone already living at high altitude, this is less of a concern since your body has already adapted. But traveling to a mountain resort for a ski trip or hiking vacation and immediately pushing yourself at elevation adds unnecessary risk in the first trimester.
How Hard Is Too Hard
There’s no single heart rate cutoff that applies to every pregnant person. The old advice of “stay under 140 beats per minute” has been retired because fitness levels vary so widely. Instead, the current standard is moderate intensity, meaning you can carry on a conversation while exercising but wouldn’t be able to sing. If you were already doing vigorous workouts before pregnancy, you can generally continue them, though ACOG notes that pushing beyond roughly 85% of your maximum capacity enters territory where the effects on the fetus aren’t well studied.
Jerky, bouncy, or high-impact movements also deserve caution. Your center of gravity shifts as pregnancy progresses, but even in the first trimester, the combination of relaxin-loosened joints and lower blood pressure can make quick directional changes or plyometric jumps feel different than they used to. If a movement feels unstable, trust that instinct.
Warning Signs to Stop Immediately
Regardless of the exercise you choose, certain symptoms mean you should stop right away: vaginal bleeding, fluid leaking, regular painful tightening in your abdomen, chest pain, a sudden bad headache, dizziness or feeling faint, trouble catching your breath beyond what’s normal for the workout, or a rapid or irregular heartbeat. Muscle weakness that makes you lose your balance, pain or swelling in your lower leg, and feeling generally “not right” are also reasons to stop and get checked. These apply at every stage of pregnancy, not just the first trimester.
What’s Actually Safe
The list of what you can do is much longer than the list of what you can’t. Walking, swimming, stationary cycling, low-impact aerobics, modified strength training, and prenatal yoga in a normal-temperature room are all well-supported options. Staying active during the first trimester helps with fatigue, mood, sleep, and sets you up for an easier time as pregnancy progresses. The goal isn’t to dial everything back to nothing. It’s to cut out the specific activities where the risks clearly outweigh the benefits: contact, heat, pressure changes, extreme altitude, and movements that compromise your stability.