Running during pregnancy: safe tips and modifications

Photo by Pavel Danilyuk on Pexels

You’re eight weeks along, you’ve just told your GP you run, and the response was some version of “that should be fine, just listen to your body” — which is technically true and completely unhelpful when you’re standing in your kitchen at 6am wondering if today’s 5k is a good idea or a reckless one.

Here’s the actual answer: if you were running regularly before you got pregnant and your pregnancy is progressing without complications, continuing to run is generally considered safe — for most of it, most weeks. But “safe” doesn’t mean “unchanged.” Your body is doing something enormous, and the running that got you through last year’s half marathon needs to bend to that, not fight it.

This isn’t a piece about whether you’re allowed to run. It’s about what running during pregnancy safe tips and modifications actually look like week to week, trimester to trimester — the practical stuff nobody tells you until you’re already three months in and confused.

The baseline rule: continue, don’t start big

If you were already running before conception, most guidance — including from the NHS and the American College of Obstetricians and Gynecologists — supports continuing at a similar or slightly reduced level, provided your pregnancy is low-risk. What you shouldn’t do is use pregnancy as the moment to chase a new distance PB or start marathon training from scratch. This is not the year for that.

If you’re new to running and pregnant, that’s a different conversation — brisk walking, swimming, or a gentle walk-run approach (closer to the early weeks of something like Couch to 5K, but slower and with no pressure to progress on schedule) is the more sensible starting point than launching into structured running.

Talk to your midwife or GP before continuing any exercise programme, particularly if you have any risk factors — placenta praevia, pre-eclampsia, cervical insufficiency, or a history of preterm labour are all reasons your provider may advise against running specifically.

Trimester by trimester: what actually changes

Nothing changes overnight, but the adjustments compound.

The relaxin point matters more than people realise. This hormone loosens your ligaments to prepare your body for birth, but it doesn’t discriminate — your ankles, knees, and hips get looser too, which raises the risk of rolling an ankle on uneven ground. If you normally run trails, this might be the season to stick to pavement or a track.

The heart rate myth you can ignore

For years, pregnant runners were told to keep their heart rate under 140bpm. That guidance has been dropped by most major health bodies because it doesn’t account for individual fitness — a well-trained runner’s 140bpm is a different intensity to someone new to exercise. Current guidance focuses on effort, not a hard number.

The practical version: use the talk test. You should be able to hold a conversation in short sentences while running. If you’re gasping single words, you’re working too hard. If this all sounds abstract, our guide on heart rate zones for running explains how effort-based training works even outside pregnancy — the same logic applies here, just with a lower ceiling.

Signs to stop immediately

This is the non-negotiable section. Stop running and contact your midwife or GP if you experience:

• Vaginal bleeding or fluid leakage
• Dizziness, feeling faint, or headache
• Chest pain or unusual shortness of breath before exertion
• Calf pain or swelling (could indicate a clot)
• Regular, painful contractions
• A noticeable reduction in fetal movement (second/third trimester)
• Sudden swelling of the face, hands, or feet

None of these mean panic. Most have benign explanations. But they all mean stop and get checked before you run again, not push through and see.

Modifications that actually help week to week

Small, unglamorous adjustments make the biggest difference here.

Slow down more than feels necessary. Your resting heart rate and blood volume are both elevated during pregnancy, meaning your heart is already working harder before you take a single stride. A pace that used to feel easy will now feel moderate. Let it.

Switch to run-walk intervals earlier than you think you need to. Something like 4 minutes running, 1 minute walking holds your effort steady without the spikes a continuous run creates. This isn’t a downgrade — it’s the same tool used in Couch to 5K programmes for good reason: it works.

Prioritise pelvic floor strength alongside running, not instead of it. Pregnancy and impact exercise both load the pelvic floor. Daily pelvic floor exercises (a physio-supervised programme is ideal, but the NHS provides basic guidance) reduce the risk of incontinence during and after pregnancy, and running with a well-conditioned pelvic floor genuinely feels different.

Fuel and hydrate more deliberately. Pregnancy increases your fluid and calorie needs beyond what running alone demands. Dehydration symptoms can be easy to miss when you’re already dealing with pregnancy fatigue — our piece on dehydration signs and prevention is worth a read even if you think you’re drinking enough.

Expect your pace to drop and let it. By the third trimester, many runners are 90 seconds to 2 minutes/km slower than their pre-pregnancy easy pace, if they’re still running at all. This is not deconditioning. It’s a body carrying significantly more weight, with a shifted centre of gravity and reduced core stability doing exactly what it’s designed to do.

What to swap in on the harder days

Some days, running just won’t be it — and that’s fine. Cross-training keeps your cardiovascular fitness ticking over without the impact:

• Swimming (particularly good in the third trimester — the water supports your weight)
• Stationary cycling at a gentle resistance
• Walking, especially with poles for extra stability late in pregnancy
• Prenatal yoga or Pilates for core and pelvic floor work

If you want more structure around this, cross training for runners covers how to blend these without losing running fitness — most of the same logic transfers to pregnancy, just at a gentler dial.

After a bad run

You’ll have runs during pregnancy that feel awful — heavy legs, breathlessness at a pace that used to feel like nothing, a wave of nausea at mile 2. This is common and doesn’t mean you’re doing it wrong. If you need a reset on how to process a rough session without spiralling into “should I even be doing this,” dealing with a bad run applies just as much here as it does to marathon training — maybe more.

The Honest Takeaway

• If you ran before pregnancy and it’s low-risk, continuing is generally supported — but expect pace, distance, and frequency to shrink as pregnancy progresses, particularly from the second trimester onward.
• Get personalised clearance from your midwife or GP, especially if you have any risk factors — this article is not a substitute for that conversation.
• Use the talk test over a heart rate number, switch to run-walk intervals earlier than feels necessary, and choose flat, even surfaces once relaxin loosens your joints.
• Know the stop-immediately list (bleeding, dizziness, chest pain, calf swelling, reduced fetal movement) and act on it without guilt or delay.
• Some weeks running won’t happen at all, and swimming, walking, or gentle cycling are not failures — they’re the sensible swap for that stage of pregnancy.

Next read: How many rest days do runners need?