Marine is 33, she's a communications consultant, and when her obstetrician told her she was eight weeks pregnant, her first question — before the baby's sex, before the due date, before everything — was: "Can I keep running?" Because Marine has been running three times a week for seven years, and the idea of stopping for nine months gave her almost as much anxiety as the idea of becoming a mother.
Her obstetrician's response was brilliant: "Not only can you, but you should. With a few adjustments."
That answer summarises the current state of science on exercise and pregnancy. The World Health Organisation, RCOG (Royal College of Obstetricians and Gynaecologists), NICE, and every major medical body in the world are unanimous: physical activity during pregnancy benefits both mother AND baby. It's not a luxury, it's not a risk — it's a medical recommendation.
Yet 60% of pregnant women in the UK reduce or stop all physical activity the moment they learn they're pregnant. Through fear. Through misguided caution. Through lack of information. Or because someone — mother-in-law, colleague, anxiety-inducing app — told them to "rest."
This guide is designed to replace fear with knowledge. Trimester by trimester, you'll know exactly what you can do, what you need to adapt, and what you must avoid.
Your trimester-by-trimester programme
- Proven benefits of exercise during pregnancy
- First trimester: maintain your habits
- Second trimester: the golden trimester for movement
- Third trimester: adapt without stopping
- Recommended exercises in detail
- Exercises that are off-limits
- Medical contraindications
- Stop signs: when to seek help
- Frequently asked questions
Proven benefits: why moving changes everything
The benefits of exercise during pregnancy aren't guesswork — they're data from hundreds of studies, compiled in meta-analyses and endorsed by health authorities worldwide.
For you:
- 40% reduction in gestational diabetes risk (Cochrane meta-analysis, 2017)
- 25-30% reduction in pre-eclampsia risk
- Significant reduction in lower back and pelvic pain
- Improved sleep and reduced third-trimester insomnia
- 50% reduction in risk of prenatal and postnatal depression
- Better weight management
- Faster postnatal recovery
- Often shorter labour (studies showing 30-60 minutes less active phase)
For your baby:
- Better tolerance of labour stress (the foetal heart is "trained" by maternal heart rate variations)
- Healthy birth weight (neither too small nor too large — exercise reduces macrosomia risk)
- Potentially enhanced neurological development (preliminary studies showing better brain development in babies of active mothers)
The official recommendation The NHS, RCOG, and WHO recommend that pregnant women without contraindications aim for at least 150 minutes of moderate-intensity activity per week — that's 30 minutes, 5 days a week. "Moderate intensity" means you can talk normally during the effort but couldn't sing. This is the "talk test."
First trimester: continue, don't start from scratch
The first trimester is often the trickiest — not in terms of exercise risks, but in terms of how you feel. Fatigue, nausea, early breathlessness (progesterone alters your breathing patterns from the first weeks) can make exercise difficult, even unthinkable on some days.
The principle: maintain, don't escalate
If you were active before pregnancy, continue at the same pace while listening to your body. Reduce intensity if needed — this isn't the time for personal bests. If you weren't active, start very gradually: walking is your best friend.
Key adjustments
Enhanced hydration. Pregnancy raises your baseline body temperature. Overheating (hyperthermia) is a genuine risk in the first trimester, the critical period of organogenesis. Drink 200-300ml before exercise, then regularly during and after. Avoid exercising in direct sun during the hottest hours.
Pre-exercise fuel. Hypoglycaemia is common in the first trimester. Never exercise on an empty stomach. A light snack 30-60 minutes before (banana, plain biscuits, cereal bar) prevents dizziness.
Absolute body listening. If you're exhausted, don't push through. Rest is part of training. A day without exercise isn't failure — it's your body telling you to recover.
Running in pregnancy If you were a regular runner before pregnancy, you can continue through the first trimester. Slow your pace to conversational running (you must be able to chat), and favour soft surfaces (trail, treadmill). Running should be reassessed in the second trimester as the bump grows — repeated impact on an already-stressed pelvic floor warrants discussion with your midwife. Many runners switch to brisk walking or the cross-trainer from around weeks 20-24.
Second trimester: the golden trimester for movement
Nausea fades, energy returns, the bump isn't yet big enough to get in the way — the second trimester is objectively the best time for physical activity during pregnancy.
New constraints to integrate
No more lying on your back after weeks 16-20. The increasingly heavy uterus compresses the inferior vena cava when you lie flat, potentially reducing blood flow to the placenta and causing dizziness or faintness. Exercises like crunches or yoga poses on your back should be replaced with side-lying or all-fours alternatives.
Relaxin is at work. This hormone, produced in increasing quantities, loosens your ligaments and joints to prepare the pelvis for birth. Useful for delivery — but it increases the risk of sprains and joint injuries. Avoid sudden movements, extreme stretches, and quick changes of direction.
Your balance shifts. Your centre of gravity moves forward as the bump grows. Exercises requiring good balance (road cycling, dance classes with spins) become riskier.
Pelvic floor exercises: the non-negotiable Your pelvic floor carries the increasing weight of the uterus, baby, and amniotic fluid. Strengthening it during pregnancy reduces the risk of postnatal urinary incontinence and aids recovery. Exercise: contract your pelvic floor muscles (as if stopping a wee mid-flow), hold for 5 seconds, release for 5 seconds. 10 repetitions, 3 times daily. You can do them anywhere — on the bus, at your desk, watching telly. Nobody will notice.
Third trimester: adapt without stopping
The third trimester is when the temptation to stop is strongest. The bump is substantial, breathing is laboured, your back aches, and sleep is fragmented. Yet this is precisely when physical activity brings the greatest benefits: it relieves pain, improves sleep, prepares the body for labour, and reduces postnatal depression risk.
Essential adjustments
Reduce intensity, increase frequency. Twenty minutes of walking daily is better than 45 minutes three times a week. Shorter, more frequent sessions are better tolerated.
Prioritise buoyancy. Swimming and aquanatal classes become queen in the third trimester. Water supports your weight, relieves pressure on joints and pelvic floor, and reduces leg swelling through hydrostatic pressure.
Work on pelvic mobility. The birth ball (Swiss ball) is your best tool. Sitting on it, make circles with your pelvis, rock back and forth, move in figure-eights. These movements promote pelvic mobility, relieve the lower back, and can help the baby position well for birth.
Third trimester precaution From week 37 (early term), some midwives recommend avoiding intense exercise that could trigger premature contractions. Walking, gentle swimming, and prenatal yoga remain appropriate right up to labour. If you experience regular contractions during or after exercise, stop and contact your maternity unit.
Recommended exercises in detail
Swimming — the perfect exercise
Swimming ticks every box: cardiovascular workout, full-body strengthening, zero impact, buoyancy that relieves the extra weight. Front crawl and backstroke are the most recommended strokes. Breaststroke is possible but may be uncomfortable if you have pubic symphysis pain. Aquanatal classes — pregnancy-specific group sessions — are an excellent social and physical option. Many local leisure centres offer these, often for free on the NHS.
Walking — universally accessible
No equipment needed, no gym required, can be done until the very last day. Brisk walking (4-5 mph) is an effective cardiovascular exercise with virtually zero risk. Invest in good walking shoes with decent cushioning — your feet swell during pregnancy and your arches flatten.
Prenatal yoga — body and mind
Prenatal yoga isn't regular yoga with a bump. It's an adapted practice combining safe postures, deep breathing, and mental preparation for birth. Standing poses (warrior, tree) strengthen the legs. Floor poses (butterfly, cat-cow) loosen the pelvis. Ujjayi breathing prepares you to manage contraction pain. Many NHS trusts offer free or subsidised classes.
Stationary bike or cross-trainer — the cardio alternative
Road cycling is discouraged from the second trimester (fall risk). The exercise bike and cross-trainer are excellent alternatives: no fall risk, controllable intensity, no impact.
Light strength training — underrated and essential
Adapted strength training is one of pregnancy's most beneficial — and most underrated — exercises. Squats, lunges, arm exercises with light dumbbells (1-3kg), side planks (not front planks), resistance band work. The goal isn't performance — it's structural support: your back, legs, and pelvic floor are carrying increasing weight. Strengthening them is protecting them.
Exercises that are off-limits
Certain activities carry unacceptable risks during pregnancy — regardless of your fitness level.
Contact sports: martial arts, boxing, rugby, football, netball, basketball. The risk of abdominal trauma is unacceptable.
Sports with fall risk: downhill skiing, water skiing, surfing, horse riding, road cycling (from second trimester), lead climbing. The risks are twofold: direct trauma and placental abruption from violent impact.
Scuba diving: strictly contraindicated throughout pregnancy. The foetus cannot eliminate dissolved nitrogen during decompression — the risk of foetal gas embolism is real and serious.
Exercise at altitude (above 2,500m): reduced oxygen availability limits supply to the foetus. Brief stays at moderate altitude are acceptable if you're acclimatised, but intense exercise at altitude is not.
Hot yoga, saunas, hot tubs: hyperthermia (core temperature above 39°C) is teratogenic in the first trimester and can cause fainting throughout pregnancy. Bath temperature should stay at or below 37°C.
Medical contraindications
Certain medical conditions require strict rest — exercise is then formally contraindicated. This decision is always made by your consultant, GP, or midwife.
Absolute contraindications (RCOG):
- Threatened premature labour (regular contractions, shortened cervix)
- Premature rupture of membranes
- Placenta praevia (after week 26)
- Pre-eclampsia / severe pregnancy-induced hypertension
- Cervical insufficiency / cervical cerclage
- Severe intrauterine growth restriction
- Complicated multiple pregnancy
- Unstable cardiac or respiratory disease
Stop signs: when to seek help immediately
During exercise, certain symptoms should make you stop immediately and seek medical advice:
- Vaginal bleeding
- Leaking amniotic fluid
- Regular, painful contractions
- Chest pain or palpitations
- Dizziness, faintness, blurred vision
- Disproportionate breathlessness (you can't speak at all)
- Calf pain with swelling (risk of deep vein thrombosis)
- Sudden, severe headache
- Reduced baby movements after exercise
These symptoms don't necessarily mean something is seriously wrong — but they warrant prompt medical assessment. A "just in case" visit is always better than a missed complication.
After birth: returning to exercise Postnatal exercise doesn't start the day after delivery. Pelvic floor rehabilitation is the essential first step — typically beginning 6-8 weeks after birth, with a referral from your GP or health visitor. Before this, gentle walking is the only recommended exercise. After pelvic floor sign-off, the return to sport is gradual: swimming first, then strengthening, then impact cardio (running) — typically not before 3-4 months postnatal, and always after medical clearance. The NHS postnatal check at 6-8 weeks is your opportunity to discuss return to exercise.
Frequently asked questions about exercise during pregnancy
Can I continue running during pregnancy?
If you were a regular runner before pregnancy, you can generally continue through the first and into the second trimester, reducing your pace to conversational speed and favouring soft surfaces (trail, treadmill). From around weeks 20-24, as the bump grows, many healthcare professionals recommend switching to brisk walking or the cross-trainer to protect the pelvic floor. If you've never run, pregnancy isn't the time to start. Speak to your midwife for personalised advice.
Are abdominal exercises forbidden during pregnancy?
Traditional ab exercises (crunches, sit-ups, front planks) are indeed discouraged from the second trimester: they increase intra-abdominal pressure and can contribute to diastasis recti (separation of the abdominal muscles). However, deep transverse work (the forced exhalation that draws the navel inward), side planks, and all-fours exercises are recommended and actively protect your core.
How much exercise per day is recommended?
The NHS and WHO recommend at least 150 minutes of moderate-intensity activity per week — roughly 30 minutes, 5 days a week. This isn't a compulsory minimum: any activity is better than none. If you can only manage 15 minutes of walking three times a week, that's already beneficial. Consistency matters more than performance.
Can swimming cause an infection?
No. Public swimming pools in the UK meet strict hygiene standards (controlled chlorination). The infection risk is negligible. The only consideration is vaginal thrush, which is more common during pregnancy: dry yourself thoroughly after swimming and don't sit in a wet costume. Sea swimming is also safe and beneficial — just be mindful of currents and water temperature.
Can I do weight training with dumbbells?
Yes, with light to moderate weights (1-5kg) and controlled movements. Avoid heavy loads, exercises involving intense pushing effort (Valsalva manoeuvre), and lying flat on your back after week 16. Strength training protects your back, joints, and pelvic floor. Many gyms offer adapted programmes for pregnant women, and several excellent YouTube channels provide free prenatal strength workouts.
Can exercise cause a miscarriage?
No. There is no scientific evidence linking moderate physical activity to an increased risk of miscarriage. First-trimester miscarriages are in the vast majority of cases caused by chromosomal abnormalities — not exercise. This fear is unfounded but extremely widespread, and it unfortunately prevents many women from benefiting from physical activity during pregnancy.
What's the maximum heart rate I shouldn't exceed?
The old recommendation of not exceeding 140 bpm has been abandoned — it was too rigid and didn't account for individual fitness levels. The current guidance is the "talk test": you should be able to hold a conversation during exercise. If you're too breathless to talk, reduce the intensity. A heart rate monitor can help you gauge effort, but it's not essential. The RCOG emphasises perceived exertion over specific heart rate targets.