Exercise by trimester: first trimester exercises, then the second and third

Search for first trimester exercises and you'll find three neat lists, one per trimester, each with its own rules. The official guidance isn't written that way. ACOG, the WHO and the NHS mostly give one set of rules for the whole pregnancy, plus a handful of points that kick in at particular stages. This post covers exactly those points and labels everything else as what it is: the same advice, all nine months.

That's less content than a trimester-by-trimester listicle. It's also the part you can trust. Training that shifts as pregnancy goes on is a good use of a plan that adjusts to how you actually trained, but what changes, and when, should come from the guidance and your care provider, not from a template.

First: check with your doctor, midwife or a pelvic health physiotherapist before starting, continuing or changing exercise at any stage of pregnancy, and again whenever something changes. Everything below assumes an uncomplicated pregnancy. Nothing here is medical advice.

What stays the same in every trimester

Most of the guidance applies from the first week to the last.

• ›How much: the WHO recommends that all pregnant and postpartum women without contraindication do regular physical activity throughout pregnancy, at least 150 minutes of moderate-intensity aerobic activity through the week, and a variety of aerobic and muscle-strengthening activities (Bull et al., 2020). The NHS says aim for 150 minutes a week and try to include 2 strength sessions (NHS).
• ›How hard: ACOG suggests rating of perceived exertion over heart-rate targets, with moderate intensity at 13–14 ("somewhat hard") on the Borg scale, and the talk test as a check (ACOG, 2020).
• ›What to avoid throughout: contact activities with a high risk of abdominal trauma or imbalance, and scuba diving (ACOG); sports with a risk of falling or bumping your tummy, and exercising on an empty stomach (NHS).
• ›Warning signs: the same list applies every week, quoted in full further down.

If you were following a plan for strength and running before pregnancy, that's the frame you adapt from, trimester after trimester. And if you want the longer view of why lifting matters across the decades, strength training for women over 40 covers it.

First trimester exercises: what the guidance says

Here's the honest answer: there's no separate list of first trimester exercises. ACOG's examples of exercises extensively studied in pregnancy and found safe and beneficial are walking, stationary cycling, aerobic exercises, dancing, resistance exercises with weights or elastic bands, stretching, and hydrotherapy or water aerobics (ACOG, 2020). That list isn't labelled by trimester.

First trimester workout restrictions

The one point ACOG ties specifically to the first trimester is heat. It says pregnant women should stay well hydrated, wear loose-fitting clothing, and avoid high heat and humidity to protect against heat stress, "particularly during the first trimester". It adds that prolonged exercise belongs in a thermoneutral or air-conditioned environment (ACOG, 2020). The WHO also says to avoid physical activity in excessive heat, especially with high humidity, and to drink water before, during and after.

In practice: summer midday sessions and hot rooms are the obvious things to move or skip.

The other early-pregnancy point is about what's new, not what trimester you're in. The NHS says to start any new exercise gently, that it's usually fine to keep doing activities you already do, and that starting a new vigorous activity such as running isn't recommended (NHS). If you weren't active before, it suggests starting with about 10 minutes a day and building slowly.

A first trimester workout plan

This is an illustration, not a prescription; agree it with your care provider. For someone who was active before pregnancy, the first trimester week can look a lot like the week before:

The full version, with exercises, is in a workout plan during pregnancy. The first trimester changes are about heat, fuel and listening to how you feel, not about a new exercise list.

Second trimester exercises: when lying flat starts to matter

The clearest stage-specific rule in the guidance is about lying on your back, and the three sources time it differently.

Sources: Bull et al., 2020, ACOG, 2020 and the NHS.

The WHO's line is the earliest. If you want one rule that satisfies all three, move flat-on-your-back work out of your sessions once you're past the first trimester, and ask your care provider if you're unsure.

The swaps are simple:

• ›Flat bench press → incline press
• ›Floor glute bridges or crunches → standing, seated or side-lying alternatives
• ›Lying stretches → seated or side-lying versions
• ›Post-workout lie-down → sit or lie on your side

Harder sessions in the middle of pregnancy

ACOG says vigorous-intensity exercise into the third trimester appears safe for most healthy pregnancies, but that more research is needed on vigorous exercise in the first and second trimesters and on intensity above 90% of maximum heart rate (ACOG, 2020). That's a gap in the evidence, not a ban. If your training includes hard intervals or heavy sessions, that's a specific conversation to have with your care provider.

Third trimester exercise: what changes late in pregnancy

Late pregnancy is where most of the practical changes come from your body rather than from a rule.

Switching modes. The NHS says that as your bump grows you may find it more comfortable to change to different types of exercise, for example brisk walking instead of running, and that swimming can relieve pressure on your muscles and joints (NHS). ACOG mentions water exercise as an alternative when low-back pain shows up.

Posture and load. ACOG describes weight gain and a shift in center of gravity leading to progressive lordosis (a deeper curve in the lower back), which increases the forces across joints and the spine during weight-bearing exercise. It says more than 60% of pregnant women experience low back pain, and that strengthening abdominal and back muscles could minimize this risk (ACOG, 2020). That's a reason to keep some back and trunk work in, at a load that feels manageable.

Intensity. ACOG's position on vigorous exercise into the third trimester is above: it appears safe for most healthy pregnancies. It also notes that women who continued to exercise vigorously in the third trimester were more likely to deliver babies weighing 200–400 g less than comparable controls, without an increased risk of fetal growth restriction (ACOG, 2020). If you're training hard late in pregnancy, your care provider should know.

How long to keep going. None of the three sources gives a date to stop for an uncomplicated pregnancy; ACOG's position is that vigorous exercise into the third trimester appears safe for most healthy pregnancies, and the NHS says to listen to your body and not push yourself too hard.

Late pregnancy is also when it's worth thinking ahead. Recovery depends on the kind of birth you have, and exercise after a C-section follows a slower timeline than a straightforward vaginal birth. For everyone, postpartum workouts restart from walking and pelvic floor work, not from where you left off.

Warning signs, in every trimester

ACOG's Box 3, "Warning Signs to Discontinue Exercise While Pregnant", word for word (ACOG, 2020):

• ›"Vaginal bleeding"
• ›"Abdominal pain"
• ›"Regular painful contractions"
• ›"Amniotic fluid leakage"
• ›"Dyspnea before exertion" (dyspnea means shortness of breath)
• ›"Dizziness"
• ›"Headache"
• ›"Chest pain"
• ›"Muscle weakness affecting balance"
• ›"Calf pain or swelling"

The NHS adds: "stop if you feel uncomfortable, too hot or unwell."

None of these are trimester-specific. If any happen, stop and contact your doctor or midwife.

Exercise by trimester, in one table

Anything else you read with a trimester label attached, ask where it came from.

Beyond pregnancy

Training changes shape again at every stage of life, and the evidence-first approach carries on. Decades later, lifting through perimenopause applies the same principles to a different set of questions.

How exrsz handles this

exrsz builds a periodized plan from your goal, schedule, level and equipment, balances running and lifting in one plan, adapts each week to how you actually trained, and reshuffles missed sessions. It doesn't give medical advice or decide what's safe in your pregnancy. Check with your doctor, midwife or a pelvic health physiotherapist, then plan around what they've agreed.

FAQ

What first trimester exercises are safe?

The guidelines don't have a separate first trimester list. ACOG's examples of exercises studied and found safe in pregnancy include walking, stationary cycling, aerobic exercise, dancing, resistance exercise and water exercise (ACOG, 2020). Check with your care provider first.

Are there first trimester workout restrictions?

ACOG singles out heat in the first trimester: stay hydrated, wear loose clothing, and avoid high heat and humidity (ACOG, 2020). The NHS says not to start a new vigorous activity like running in pregnancy (NHS).

When should I stop doing exercises lying on my back?

The WHO says avoid supine activities after the first trimester (Bull et al., 2020), ACOG flags long periods lying flat after 20 weeks, and the NHS says no more than a few minutes in later pregnancy (NHS). Ask your care provider which applies to you.

What third trimester exercise is recommended?

The same activities as earlier, adjusted for comfort. The NHS suggests brisk walking may feel better than running as your bump grows and that swimming can relieve pressure on muscles and joints (NHS), and ACOG says vigorous exercise into the third trimester appears safe for most healthy pregnancies (ACOG, 2020).

Do second trimester exercises need to change?

Mostly the position, not the exercise. Move work off your back: the WHO says avoid supine activity after the first trimester, and ACOG flags long periods lying flat after 20 weeks (ACOG, 2020).