Is It Safe to Exercise While Pregnant?
A Trimester-by-Trimester Guide, Written By Abi Jettner, Physiotherapist at Hatched House
There is no shortage of advice once you're pregnant, and a lot of it contradicts itself. Rest more. Stay active. Don't lift anything heavy. Build strength for labour. Don't raise your heart rate too much. And of course the loudest and most frequently discussed advice; '“definitely don't lie on your back.”
It's a reasonable thing to feel confused about. Some of this advice is understandably protective. Some of it is inherited caution that has outlived the evidence behind it. This blog post walks through what's actually supported by current research, trimester by trimester, including a close look at the "don't lie on your back" rule, where it came from, what it actually means, and what recent, high-quality research says.
In short: for most pregnant women without a contraindication, exercise is not just safe, it's one of the more protective things you can do, reducing risk of gestational diabetes, excessive weight gain, caesarean birth and postnatal depression.
What changes each trimester is less "can I" and more "how does this feel and what needs adjusting." On the specific question of lying on your back: RANZCOG's actual guidance is to avoid prolonged supine positioning, not all of it, and the most recent research, including a 2025 study co-authored by leading pelvic health researcher Kari Bø, found no evidence that brief, tolerated supine exercise, even heavy resistance training, compromises the baby. If you feel dizzy, nauseated or unwell lying on your back, that's your body telling you to roll onto your side, not evidence that the position itself is dangerous for everyone, for any length of time.
Below, we've answered the questions we hear most often from pregnant clients about exercise, organised by trimester and by the specific things people are anxious about.
Is Exercise Actually Safe During Pregnancy?
Yes, for the large majority of pregnant women. The Australian Guidelines for Physical Activity in Pregnancy and Postpartum, developed by Sports Medicine Australia with the Royal Australian and New Zealand College of Obstetricians and Gynaecologists and other professional bodies, are unambiguous: physical activity in pregnancy is safe, has real health benefits for both mother and baby, and may reduce the risk of several pregnancy complications, including gestational diabetes and pre-eclampsia.
The bigger issue in Australia isn't women exercising unsafely, it's women stopping altogether out of caution that isn't evidence-based. Most pregnant women reduce or eliminate exercise during pregnancy, often on the advice of well-meaning but outdated guidance.
Is It Safe to Exercise in the First Trimester?
Yes, and if you were already active before conceiving, there's no need to scale back simply because you're now pregnant. What typically changes in the first trimester isn't safety, it's capacity. Nausea, fatigue and tender breasts can make your usual session feel much harder than it did a month ago.
This is a good trimester to shift your expectation from performance to consistency. Shorter sessions, more rest between sets, and permission to swap a run for a walk on the days you feel rough are all reasonable. If you weren't exercising before pregnancy, this is also a fine time to start, just begin gently and build gradually, rather than starting with anything high-intensity.
Is It Safe to Exercise in the Second Trimester?
For most women, yes, and this is often the trimester where things feel easiest. Nausea typically settles, energy tends to return, and the physical size of the bump hasn't yet started interfering with balance and range of motion the way it will later on.
This is a good window to build strength, particularly through the back, glutes and core, ahead of the physical demands of the third trimester and early motherhood. It's also when balance starts to shift as your centre of gravity moves, so activities with a real fall risk, think icy trail runs, unstable surfaces, or anything requiring quick direction changes may deserve a bit more caution than they did before.
Is It Safe to Exercise in the Third Trimester?
Yes, with sensible adjustments rather than a wholesale stop. Ligament laxity increases, your centre of gravity has shifted substantially, and simply carrying more weight changes how effortful everything feels. RANZCOG's patient guidance recommends working at a moderate intensity (a rating of perceived exertion around 12 to 14 out of 20), meaning you can hold a conversation but would struggle to sing, rather than chasing a specific heart rate number, which was the old standard and has since been dropped because it doesn't account for how much heart rate varies between individuals in pregnancy.
Balance-dependent and high-fall-risk activities are worth stepping back from here, and expect your body to ask for more rest between efforts. Pelvic floor and core-aware technique becomes more important as intra-abdominal pressure increases, which is where a pregnancy-specific program is genuinely useful rather than just a nice-to-have.
Is It Safe to Lie on My Back While Exercising During Pregnancy?
For most healthy pregnant women, briefly, yes. This is worth unpacking properly, because it's one of the most search-worthy and most confusingly-answered questions in prenatal exercise.
The caution around lying flat (supine) comes from a real physiological phenomenon called aortocaval compression, or supine hypotensive syndrome. As the uterus grows, lying flat on your back can allow it to press on the inferior vena cava, being the large vein returning blood from your lower body to your heart, and sometimes the aorta as well. This can reduce blood return to your heart, which can, in some women, cause a drop in blood pressure, dizziness or nausea. It is a real mechanism, and it's worth understanding correctly: it's about compression of major abdominal vessels supplying the heart, not anything to do with blood vessels in the neck.
Where things get murky is in how that mechanism has been translated into blanket advice. RANZCOG's actual clinical guidance is that women should avoid supine exercise for prolonged periods of time in the second and third trimester — which is meaningfully different from "never lie on your back after 16 weeks," a stricter rule that has become common in fitness settings but doesn't reflect what the college itself says.
Even the major guidelines can't agree; the UK says after the first trimester, the US's ACOG says after 20 weeks, most international standards land on 16 weeks, Australia's own RANZCOG gives no week at all and just says avoid "prolonged" positioning, and Canada's guideline dropped a cutoff altogether in favour of "stop if you feel unwell". When respected bodies across five countries can't agree on so much as which trimester, that's a strong sign the number itself was always a cautious guess, not a figure backed by consistent evidence.
Why Do People Say Not to Lie on Your Back in Pregnancy and Is That Still True?
Because for decades, the safest assumption was to avoid the position altogether, given the plausible mechanism above. But a plausible mechanism isn't the same as demonstrated harm, and the research asking that direct question has been catching up.
A 2019 systematic review by Michelle Mottola and colleagues, published in the British Journal of Sports Medicine, looked specifically at whether supine exercise is associated with adverse outcomes for mother or baby. The honest finding was that the evidence was too limited and of too low quality to say either way — not that supine exercise was proven safe, and not that it was proven harmful. What it did make clear is that the strict rules many of us have been given were built on caution and consensus opinion, not strong data.
The research since has moved in a reassuring direction. In 2025, a team led by Emilie Dalhaug and Kari Bø, some of the most respected researchers in women's health physiotherapy, published a study in BMJ Open Sport & Exercise Medicine examining what actually happens to the baby during heavy-load resistance training performed in supine, including a supine bench press. This was the largest study of its kind to date: 48 pregnant athletes, all experienced in heavy training, were monitored for fetal heart rate and uterine and umbilical blood flow before and after their sessions. Fetal heart rate stayed within the normal range throughout. Blood flow to the baby was not compromised. One participant briefly experienced symptoms of supine hypotension and felt fine again shortly after sitting up, which is exactly how the body is meant to respond. The researchers' conclusion was that experienced, healthy pregnant women could safely perform heavy resistance training, including supine exercise, without jeopardising the baby's wellbeing.
The practical takeaway isn't "ignore the caution altogether." It's that the position itself, tolerated briefly and modified when your body tells you to, is not the danger it's sometimes made out to be, and your own symptoms are a far better guide than a fixed number of weeks.
Does That Mean I Can Do Pilates Reformer Work Lying on My Back?
Generally, yes, which is exactly why it remains part of well-designed pregnancy Pilates programming throughout pregnancy. Reformer exercises performed supine are typically brief, a matter of one or two minutes per exercise, not sustained lying, and a good instructor will have you change position well before any symptoms could develop, adjusting further if you report feeling unwell.
The instruction to listen to your body still applies, and it's a better instruction than a hard cut-off. If lying on your back ever brings on dizziness, nausea, breathlessness or that unmistakable unwell feeling, roll onto your side immediately. Symptoms will resolve the symptoms within a minute or two, and it's a sign to modify that particular exercise going forward, not a sign that something has gone wrong.
Is Lying Flat on Your Back for Exercise the Same as Sleeping on Your Back?
No, and this distinction matters because the two get conflated often. Sleep position research is a separate, and stronger, body of evidence. Studies including the New Zealand Multicentre Stillbirth Case-Control Study found an association between going to sleep on your back in later pregnancy and increased stillbirth risk, and this is why the advice to fall asleep on your side in the third trimester still stands and is genuinely evidence-based.
Sleep and brief, awake exercise are physiologically different situations. Hours of unconscious, unmonitored positioning versus a minute or two of active, awake movement where you notice and respond to any symptoms immediately. The evidence questioning the exercise rule does not extend to, or contradict, the sleep position advice. Keep sleeping on your side; the flexibility is specifically about brief exercise positioning.
What Exercises Should I Avoid During Pregnancy?
Genuinely contraindicated activities are fewer than most people assume, and a lot of commonly avoided things are more "use judgement" than "never." Common sense exclusions include contact and collision sports, activities with a high fall risk such as downhill skiing or horse riding if you're new to them, scuba diving, and exercise in extreme heat or humidity, particularly in the first trimester.
A 2020 systematic review by Victoria Meah, Gregory Davies and Margie Davenport in the British Journal of Sports Medicine looked specifically at which medical conditions genuinely warrant stopping or restricting exercise. Their key finding was that most conditions previously listed as contraindications were based on expert opinion rather than evidence of actual harm. They identified genuine absolute contraindications, including conditions like severe cardiorespiratory disease, placental abruption, uncontrolled type 1 diabetes, active preterm labour, severe pre-eclampsia and cervical insufficiency. However, they also noted several commonly restricted conditions, including gestational hypertension and twin pregnancy, may actually benefit from continued, modified activity rather than rest.
The message from this research is consistent: modify rather than stop by default, and have the conversation with your GP, obstetrician or a women's health physiotherapist about your specific situation rather than assuming restriction is automatically the safer choice.
Is It Safe to Lift Weights or Strength Train While Pregnant?
Yes, and current research is increasingly positive about it. Strength training supports posture, reduces back and pelvic pain, helps manage gestational weight gain, and builds the physical capacity that labour and early motherhood both demand.
RANZCOG's guidance recommends one to two sets of twelve to fifteen repetitions per exercise, performed at that same moderate perceived exertion, with slow, controlled movement and good technique prioritised over-load. The Strong Mama research from Norway, discussed above, found that even genuinely heavy resistance training was well tolerated by experienced athletes with normal foetal responses, which is reassuring context, though most recreational exercisers should still be working at a comfortably challenging rather than maximal intensity, and ideally under guidance if strength training is new to them.
What Are the Warning Signs to Stop Exercising and See Someone?
A small list of symptoms should prompt you to stop and seek medical advice, rather than push through. These include vaginal bleeding, fluid leaking, regular painful contractions, dizziness or feeling faint, chest pain, headache, calf pain or swelling on one side, and a noticeable reduction in your baby's movements.
These are genuine reasons to stop and be assessed, not reasons to be fearful of exercise generally. Most pregnant women will never experience any of them.
Do I Need Pelvic Floor Exercises During Pregnancy?
Yes, and this is worth building in from early pregnancy rather than waiting until symptoms appear. Increasing weight, hormonal changes to connective tissue, and the growing pressure of the uterus all place additional demand on the pelvic floor well before birth itself does.
Learning to correctly contract and, just as importantly, correctly relax the pelvic floor is genuinely a trainable skill, and getting the technique right in pregnancy sets you up far better for the postnatal period than starting from scratch after birth.
When Should I See a Women's Health Physiotherapist During Pregnancy?
Ideally at some point in the second trimester if nothing is bothering you, and immediately if something is. A physiotherapist assessment can confirm your pelvic floor technique, screen your musculoskeletal health, and tailor exercise to your specific pregnancy rather than a generic timeline.
Earlier assessment is worthwhile if you're experiencing pelvic girdle pain, back pain, any bladder or bowel symptoms, or if you have a specific medical complexity and are unsure what modifications you need.
Further Frequently Asked Questions:
Can I start exercising for the first time now that I'm pregnant?
Yes. Pregnancy is a reasonable time to begin, provided you start gently (brisk walking, swimming or a pregnancy-specific class are sensible entry points ), and build gradually rather than beginning with anything high-intensity.
Can I keep running while pregnant?
If you were running regularly before pregnancy, most women can continue, adjusting pace and distance to how you feel and reassessing as balance and joint laxity change later on. Starting running for the first time during pregnancy is not generally recommended; walking is the better starting point.
Will exercise cause a miscarriage?
No. There is no evidence that exercise, including vigorous exercise in women who were already regularly active, increases miscarriage risk. Most first-trimester miscarriages are related to chromosomal factors unrelated to activity levels.
Can exercise bring on labour early?
No credible evidence supports this for healthy, uncomplicated pregnancies. Regular exercise throughout pregnancy is not associated with earlier onset of labour.
Is hot yoga or a heated Pilates studio safe during pregnancy?
It's generally advised against, particularly in the first trimester, due to the risk of overheating. A standard-temperature studio is a better choice, along with good hydration and stopping if you feel overheated at any point.
Do I need my doctor's clearance before exercising?
If you have no complications, formal clearance usually isn't required to begin gentle to moderate activity, though it's worth mentioning at your next appointment. If you have a pre-existing medical condition or pregnancy complication, speak with your GP or obstetrician first about what's appropriate for you.
Supporting You Through an Active Pregnancy at Hatched House
Good pregnancy exercise advice isn't about a fixed set of rules applied to every woman regardless of her history, her fitness background or how she's actually feeling that week. It's about understanding the real evidence, knowing which cautions are genuinely protective and which have simply been repeated for years without being questioned, and building a program around your body specifically.
Our physiotherapist-led Clinical Pilates classes are tailored to every stage of pregnancy, and we can assess your pelvic floor and musculoskeletal health, answer questions specific to your pregnancy, and help you stay active safely and confidently right through to birth.
Hatched House provides nurturing, excellent and ethical women's healthcare, supporting women through fertility, pregnancy, motherhood and beyond, in an inclusive, multidisciplinary environment.