Safe Exercise During Pregnancy: A Trimester-by-Trimester Guide

For most of medical history, pregnant women were advised to rest, avoid exertion, and treat pregnancy as a state of physical fragility. That advice was not based on evidence. The current position of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) and Sports Medicine Australia is clear: regular moderate-intensity exercise during uncomplicated pregnancy is safe, beneficial, and recommended.

The benefits extend to both mother and baby. For the mother, regular exercise during pregnancy reduces the risk of gestational diabetes, pre-eclampsia, excessive gestational weight gain, and postnatal depression. It improves sleep quality, reduces back and pelvic pain, maintains cardiovascular fitness, and supports faster postpartum recovery. For the baby, maternal exercise is associated with healthier birth weight and improved cardiovascular development.

None of this means exercise during pregnancy is without nuance. The right type, intensity, and volume of exercise changes across the trimesters, some activities carry specific risks that warrant modification or avoidance, and certain conditions mean exercise needs to be discussed with your care team before proceeding. This guide covers all of it, trimester by trimester.

General principles across all trimesters

Before getting into trimester-specific guidance, several principles apply throughout pregnancy.

The current recommendation. RANZCOG recommends that pregnant women without contraindications accumulate at least 150 to 300 minutes of moderate-intensity aerobic activity per week, spread across most days. This is consistent with the general physical activity guidelines for all adults and is achievable through activities like walking, swimming, and cycling on a stationary bike.

Moderate intensity, not maximum effort. Moderate intensity means you can hold a conversation while exercising but are breathing more heavily than at rest. A useful guide is the talk test: if you can speak comfortably in full sentences, you're at or below moderate intensity. If you cannot speak at all, you're working too hard. In the second and third trimesters particularly, the goal is sustained moderate effort rather than high-intensity intervals.

Listen to your body. This is not a vague platitude — it is specific and important. Pregnancy changes how your body responds to exercise in ways that are sometimes difficult to predict. Dizziness, significant breathlessness, chest pain, pelvic pressure, or any pain during exercise are signals to stop and rest. If symptoms persist, contact your midwife or GP.

Warm up and cool down properly. The hormone relaxin increases joint laxity throughout pregnancy, which means your ligaments are more susceptible to overstretching. A proper warm-up before exercise and a gradual cool-down afterward reduces this risk.

Stay hydrated and avoid overheating. Your core body temperature runs higher during pregnancy, and overheating is associated with adverse outcomes particularly in the first trimester. Exercise in cool, well-ventilated environments, drink water before, during, and after exercise, and avoid hot yoga, saunas, and outdoor exercise in extreme heat.

Activities that are safe throughout pregnancy

Several forms of exercise are appropriate across all three trimesters for women with uncomplicated pregnancies.

Walking. The most accessible and consistently safe exercise throughout pregnancy. Walking can be maintained at whatever pace and duration feels appropriate, and modified easily as pregnancy progresses. It requires no equipment, no gym membership, and no instruction. Most women can walk comfortably well into the third trimester.

Swimming and water exercise. Widely considered one of the best forms of exercise during pregnancy. The buoyancy of water reduces the load on your joints, which makes movement comfortable even when other activities feel heavy. Water temperature provides natural cooling. Swimming laps, water walking, and aquanatal classes are all appropriate options.

Stationary cycling. Cycling on a stationary bike removes the fall risk associated with road or trail cycling and allows you to maintain cardiovascular fitness safely throughout pregnancy. The upright position becomes less comfortable in the third trimester for some women, though recumbent stationary bikes address this.

Prenatal yoga and Pilates. Both offer significant benefits for strength, flexibility, posture, and pelvic floor function during pregnancy. Classes specifically designed for pregnancy are modified to remove poses and positions that are not appropriate at each stage. General yoga and Pilates classes can be adapted for pregnancy with a knowledgeable instructor, though a prenatal-specific class is preferable.

Strength training. Resistance exercise with appropriate modifications is safe and beneficial during pregnancy. Maintaining upper and lower body strength supports posture, reduces back pain, and contributes to faster postpartum recovery. See the trimester-specific sections below for modifications that apply.

First trimester: weeks 1 to 12

The first trimester is often the most challenging for exercise not because of physical limitations but because of how you feel. Nausea, fatigue, and the general exhaustion of early pregnancy mean that maintaining your previous exercise routine often isn't realistic. This is normal and temporary.

What's appropriate: If you were exercising regularly before pregnancy, you can generally continue your routine at the same intensity with a few modifications. If you were not exercising regularly, this is a reasonable time to introduce gentle exercise like walking, swimming, or prenatal yoga.

Modifications to make from the start: Avoid exercises involving significant impact to the abdomen, contact sports, and activities with a high fall risk. Avoid exercising in hot environments or in extreme heat. Avoid lying flat on your back for extended periods during exercises like crunches and sit-ups — not because of the safety concerns that apply in the third trimester, but because many women find the position uncomfortable with nausea.

Managing nausea and fatigue: If nausea is severe, exercise is unlikely to be a priority and that is entirely appropriate. Even short walks when you feel able provide some benefit. As nausea eases through the first trimester, gradually increasing activity is reasonable. Do not push through significant nausea in the name of maintaining fitness.

What to watch: If you experience any bleeding or spotting during or after exercise in the first trimester, stop exercising and contact your midwife or GP promptly.

Second trimester: weeks 13 to 27

The second trimester is often the most comfortable period for exercise. Nausea has typically eased, energy has returned, and the bump is growing but not yet large enough to significantly limit movement. Many women find this is when they feel their best during pregnancy and are able to exercise most consistently.

What's appropriate: All of the activities listed above remain appropriate. Many women find the second trimester is when they establish their pregnancy exercise routine most effectively.

Modifications as the bump grows: As your centre of gravity shifts forward, balance becomes more affected and the risk of falling increases. Activities requiring significant balance, including certain yoga poses, step aerobics, and outdoor cycling on uneven terrain, need to be assessed carefully. Switching from outdoor cycling to a stationary bike is a sensible transition at this point.

Strength training modifications: Exercises performed lying on your back should be modified to an incline, seated, or side-lying position as the bump grows. Not because of established safety concerns at this stage, but because many women find lying flat becomes uncomfortable. Avoid heavy lifting that requires breath-holding and bearing down, which increases intra-abdominal pressure in ways that place load on the pelvic floor.

Pelvic floor considerations: The second trimester is when pelvic floor load increases significantly as the bump grows. High-impact activities including running and jumping can stress the pelvic floor for women who are already experiencing any leakage, pelvic heaviness, or pelvic girdle pain. If any of these symptoms are present, consult a women's health physiotherapist before continuing high-impact exercise.

Diastasis recti awareness: The abdominal muscles begin to separate in the second trimester as the uterus grows. Exercises that create significant forward bulging of the midline — including traditional crunches, sit-ups, and heavy double-leg lifts — are generally modified or avoided from this point. A women's health physiotherapist can assess your abdominal separation and advise on appropriate core exercise.

Third trimester: weeks 28 to 40

The third trimester brings the most significant physical changes and requires the most modification to exercise. The combination of a large bump, loosened joints, reduced lung capacity, and increased fatigue means that most women naturally reduce their exercise intensity and volume. This is appropriate and expected.

What's appropriate: Walking, swimming, water exercise, stationary cycling, prenatal yoga, and modified strength training all remain appropriate. Swimming in particular is often described by women in the third trimester as one of the few forms of exercise that feels genuinely comfortable, because the water supports the weight of the bump.

Lying on your back from 28 weeks: From 28 weeks, prolonged lying on your back is not recommended during exercise — consistent with the NSW Health guidance on sleep position. Modify any exercises that require lying flat to an inclined, seated, or side-lying alternative.

Reducing impact: Running and higher-impact activities become increasingly uncomfortable in the third trimester and place greater load on the pelvic floor. Many women naturally transition from running to walking in the third trimester. If running is important to you and you are managing it without pelvic floor symptoms, it can be continued at a reduced intensity and pace with your care team's knowledge.

Joint protection: Relaxin levels are highest in the third trimester and your joints are at their most lax. Exercises that require lateral cutting, single-leg balance work, and sudden directional changes carry the highest risk of joint injury. Focus on stable, controlled movements rather than dynamic and reactive ones.

Managing breathlessness: Your growing uterus reduces the space available for your lungs to expand fully, and many women find they become breathless more easily in the third trimester. Reduce intensity to accommodate this rather than pushing through significant breathlessness. The talk test remains the most useful guide.

Pelvic girdle pain and sciatica: If you have developed pelvic girdle pain or sciatica in the third trimester, your exercise options need to be discussed with a women's health physiotherapist. Certain activities including asymmetric exercises, wide-stance movements, and lunges may aggravate these conditions. Exercise remains possible and beneficial for most women with PGP but requires specific modification.

Activities to avoid during pregnancy

Certain activities carry risks during pregnancy that are not outweighed by their benefits.

Contact sports including martial arts, boxing, football, and hockey carry a risk of abdominal trauma that is not appropriate during pregnancy.

Activities with a high fall risk including horse riding, gymnastics, skiing, and mountain biking carry an obvious risk of injury that increases as the pregnancy progresses and balance is affected.

Scuba diving is contraindicated during pregnancy because decompression bubbles in the fetal circulation cannot be filtered the way they can in adults, carrying risk for the fetus.

Hot yoga and hot Pilates are not appropriate during pregnancy due to the risk of overheating. Regular yoga and Pilates in a standard temperature environment remain appropriate.

Lying flat on your back for extended periods from 28 weeks, as per NSW Health guidance on third trimester positioning.

When to stop exercising and seek advice

Stop exercising and contact your midwife or GP if you experience chest pain, difficulty breathing that is disproportionate to your effort level, dizziness or faintness, painful uterine contractions, vaginal bleeding, fluid leaking from the vagina, significant reduction in fetal movement, calf pain or swelling, or headache.

If you have any of the following conditions, discuss exercise with your care team before continuing or starting: placenta praevia after 28 weeks, cervical incompetence or cerclage, preeclampsia or pregnancy-induced hypertension, preterm labour in the current or previous pregnancy, significant heart or lung disease, or multiple pregnancy with complications.

Starting exercise if you weren't active before pregnancy

If you were not exercising regularly before pregnancy, the second trimester is the most practical time to start. Begin with low-intensity activity like walking or swimming for 15 to 20 minutes, three times per week, and build gradually. Avoid starting high-intensity exercise programs during pregnancy if you have no established fitness base.

Speak with your GP or midwife before starting a new exercise program during pregnancy, particularly if you have any health conditions or complications. They can confirm that exercise is appropriate for your specific situation and make any relevant recommendations.