Can I run while pregnant?

The verdict

Yes, and unusually the NHS names running specifically rather than leaving you to infer it.

Its instruction is to keep up your normal daily physical activity or exercise, giving sport, running, yoga, dancing or even walking to the shops and back as examples, for as long as you feel comfortable. It follows that with a sentence worth reading twice: exercise is not dangerous for your baby, and there is evidence that active women are less likely to experience problems in later pregnancy and labour.

ACOG's position is that women who habitually engaged in vigorous-intensity aerobic activity or who were physically active before pregnancy can continue these activities during pregnancy and the postpartum period, and that in the absence of obstetric or medical complications, physical activity in pregnancy is safe and desirable.

HSE Ireland names running directly too, listing walking, swimming, yoga and running among the normal daily physical activities you can keep up for as long as you feel comfortable.

The two things the NHS actually asks of you

The caveats are specific and neither is about stopping.

The first is intensity. The NHS says that as a general rule you should be able to hold a conversation as you exercise when pregnant, and that if you become breathless as you talk you are probably exercising too strenuously. Tommy's calls this the talk test and gives the same instruction: if talking makes you out of breath, slow down. ACOG's version is that at moderate intensity you can still talk normally but cannot sing.

The second is starting. If you were not active before you got pregnant, the NHS says do not suddenly take up strenuous exercise, and if you start an aerobic programme such as running, tell the instructor you are pregnant. ACOG's on-ramp for new exercisers is gentle: begin with as little as 5 minutes a day and add 5 minutes each week until you can stay active for 30 minutes a day.

How much you are aiming for

ACOG puts a number on it: ideally, pregnant women should get at least 150 minutes of moderate-intensity aerobic activity every week, which you can divide into 30-minute workouts on five days a week or into smaller 10-minute blocks throughout each day.

HSE Ireland gives a similar target of five times a week for 30 minutes or more, mixing aerobic and strengthening work, with intensity that should feel comfortable for you.

The NHS is deliberately less prescriptive, saying that exercise does not have to be strenuous to be beneficial and that 30 minutes of walking a day can be enough, but if you cannot manage that, any amount is better than nothing.

For a runner, the useful reading is that the target is low relative to normal training. You are unlikely to be under-doing it.

What changes as you go

Nothing about running becomes unsafe, but several things become uncomfortable, and knowing which is which helps.

ACOG explains that the most distinct changes are weight gain and a shift in the point of gravity resulting in progressive lordosis, and that these lead to increased forces across the joints and spine during weight-bearing exercise. It reports that more than 60 per cent of all pregnant women experience low back pain, and that strengthening abdominal and back muscles could minimise this risk.

The pelvic floor is the other one and it is the reason many runners stop before they otherwise would. The NHS states that the pelvic floor comes under great strain in pregnancy and childbirth, that weakness can cause leaking when you cough, sneeze or strain, and that all pregnant women should do pelvic floor exercises even if they have no symptoms now. Its prescription is three sets of eight squeezes every day, both fast and slow, which it suggests doing at each meal so you remember.

Leaking while running is common, is not something to be embarrassed about, and is a reason to see a physiotherapist rather than a reason to stop quietly. The NHS names obstetric physiotherapy as an available referral.

Heat, hydration and the road

The environmental advice is the most concrete part of the guidance for runners.

• The NHS says avoid any strenuous exercise in hot weather, and drink plenty of water and other fluids.
• ACOG says avoid becoming overheated, especially in the first trimester, wear loose-fitting clothing, exercise in a temperature-controlled room, and do not exercise outside when it is very hot or humid.
• HSE Ireland states that exposure to extreme temperatures during pregnancy can increase your risk of premature birth and certain birth defects, and advises against exercising in very hot or humid weather.
• The NHS also says always warm up before exercising and cool down afterwards, and do not exhaust yourself.

Trail running introduces the fall question, which the NHS handles by putting activities with a risk of falling in a caution category. Uneven ground and a shifting centre of gravity is the combination to think about, rather than running as such.

Races, altitude and the rest

Two specifics come up. On altitude, the NHS says do not exercise at heights over 2,500 metres above sea level because of altitude sickness risk; ACOG uses 6,000 feet for people who do not already live at altitude. On competition, HSE Ireland says it is best not to try for peak fitness or train for an athletic competition during pregnancy, which is the only body to address racing directly.

That is guidance about training load and goals rather than a prohibition on entering an event, and it is worth reading as such.

When to stop a run

HSE Ireland's list is the practical one. Contact your GP, midwife or obstetrician immediately if you have shortness of breath before or during exercise, chest pain or palpitations, have been feeling faint or dizzy, have regular contractions or early labour, have severe pain in the abdominal, back or pubic areas, or notice reduced movement of your baby. Any bleeding or fluid loss is the same.

Short of that, the NHS instruction is to slow down as your pregnancy progresses or if your maternity team advises it, and if in doubt, consult them.

The short version

Run. The NHS names it and says exercise is not dangerous for your baby. Use the talk test, keep out of the heat, drink, do your pelvic floor exercises daily, and get a physiotherapy referral rather than quitting if you start leaking. If you were not a runner before, walk first and build.