Exercise During and After Pregnancy: An Evidence-Based Guide

For most of medicine’s recent history, women were told to "take it easy" during pregnancy — an instinct that turned out to be exactly wrong for the majority. The modern evidence, accumulated across hundreds of trials and codified in 2018–2020 ACOG, CSEP, and IOC consensus statements, says the opposite: regular physical activity during pregnancy is one of the most effective things a healthy expectant person can do for their own health and the developing baby’s.

Why exercise in pregnancy matters

The 2018 series of systematic reviews in Br J Sports Med — the evidence base behind the Canadian Society of Exercise Physiology (CSEP) guideline — pooled hundreds of trials to quantify what exercise does for pregnant adults Mottola 2018:

• Gestational diabetes: 38% reduction in incidence in active pregnancies vs sedentary control Davenport 2018
• Preeclampsia: 41% reduction
• Hypertensive disorders of pregnancy: 39% reduction
• Excessive gestational weight gain: ~32% reduction
• Prenatal and postnatal depression: ~25% reduction in symptom severity Davenport mood 2018
• Common pregnancy discomforts (low-back pain, pelvic-girdle pain, fatigue): meaningfully reduced Davenport flags 2019
• Caesarean and instrumental delivery rates: small reductions in active pregnancies
• Newborn outcomes: no increased risk of preterm birth, miscarriage, or low birth weight; and possibly small benefits to neonatal cardiac health Davenport fetal 2019

The IOC expert group’s 2016 Lausanne consensus reached the same conclusion through different means: across recreational and elite populations, regular pregnancy exercise is protective, not risky, when reasons not to do this are absent and load is appropriate Bø 2016.

"Physical activity in pregnancy has minimal risks and has been shown to benefit most women, although some modification to exercise routines may be necessary because of normal anatomic and physiological changes and fetal requirements." — per ACOG 2020 Committee Opinion 804, the standard reference in North American obstetric practice

The recommended dose

The CSEP 2019 guideline (now the world’s most evidence-based pregnancy exercise framework, GRADE-rated and adopted internationally) is unambiguous on the target Mottola 2018:

• At least 150 minutes per week of moderate-intensity physical activity
• Spread across at least 3 days — daily activity is encouraged
• Include both aerobic and resistance training
• Add pelvic-floor muscle training daily — reduces risk of urinary incontinence by about 50%
• Avoid prolonged supine positions from mid-second trimester onward (compression of the inferior vena cava can reduce uterine blood flow)

"Moderate intensity" maps to ~12–14 on Borg’s 6–20 RPE scale — able to hold a conversation but breathing harder than at rest. The previously-popular "220 minus age × 60-70%" heart-rate target has been replaced by RPE-based prescription; pregnancy-specific HR zones (e.g. Mottola’s) exist but are not strictly necessary if RPE is monitored Mottola 2018.

Trimester-by-trimester

First trimester (weeks 1–13)

The principle: continue what you were already doing, scaled to how you feel. Nausea, fatigue, and breast tenderness frequently dominate this period, so workouts often need shortening. There is no good evidence that maintaining moderate exercise increases miscarriage risk in healthy pregnancies Davenport fetal 2019.

• Continue running/cycling/swimming/yoga at moderate intensity if these were already your routine.
• Reduce maximal-effort or competition-style sessions; aim for RPE ≤ 14.
• If you weren’t exercising before pregnancy, walking and prenatal-friendly group classes are excellent entry points.
• Hydrate generously and avoid overheating — core temperature > 39°C should be avoided in the first trimester (theoretical neural-tube risk; conservative advice).

Second trimester (weeks 14–27)

Often the most comfortable phase for exercise. Energy returns, the bump is manageable, and most women feel well. Adjustments begin:

• Stop supine exercise beyond ~16–20 weeks (lying flat on back). The expanding uterus compresses the inferior vena cava in this position. Use propped-up incline (45°+), side-lying, or all-fours instead.
• Reduce prone (face-down) exercise as the bump grows. Yoga's child’s pose, prone bird-dog progressions, etc. become impractical and uncomfortable.
• Lower the load on heavy lifts as Valsalva manoeuvre (breath-holding) becomes not recommended. Aim for 2–4 reps in reserve on resistance work.
• Watch for diastasis recti — the separation of the abdominal muscles common in mid-late pregnancy. Avoid traditional crunches and full sit-ups; use horizontal-trunk stabilisation exercises (bird dog, dead bug, side plank with knee down).
• Pelvic-floor work daily — both contracting (Kegels) and relaxing patterns. The pelvic floor takes large load throughout pregnancy and benefits from active conditioning Dietz 2007.

Third trimester (weeks 28–40)

Continue exercising for as long as it feels right. Many women run, lift, and cycle into the final weeks. Practical changes:

• Balance becomes harder. Centre of gravity shifts forward and ligamentous laxity peaks Morino 2018. Step-ups, Bulgarian split squats, single-leg deadlifts — reduce or replace with bilateral movement.
• Avoid contact sports, fall-risk activities — mountain biking, skiing, horseback riding. Avoid hot yoga, scuba diving, sky diving.
• Walking remains gold-standard: low-impact, cardiovascular benefit retained, easy to scale, and a good evidence base for late-pregnancy benefit Ruchat 2012.
• Pelvic-floor work continues right up to delivery.
• Listen to your body — fatigue, swelling, contractions, dizziness on standing all become more common signals.

Postpartum return

The most under-served phase in mainstream sports medicine. Until very recently, postpartum return-to-exercise advice was "wait 6 weeks then go" — which is wrong on both ends (most can begin gentle work earlier; most should not jump back to high-impact activity at 6 weeks).

The Goom, Donnelly & Brockwell 2019 framework (now widely adopted in pelvic-health physiotherapy) is the standard reference Goom 2019:

1. Weeks 0–6: Recovery, baby care, walking from days 1–3 (start with 5–10 min, build gradually), pelvic-floor isometric work as the abdominal incision/perineum allows.
2. Weeks 6–12: Begin structured rehab with a pelvic-floor physiotherapist if available. Add light resistance training. Build walking volume. Begin low-impact aerobic work (cycling, swimming).
3. Weeks 12+: Begin graded return to running only after passing functional tests: single-leg squat, single-leg bridge, hop test, plank hold, and absence of urinary leakage or pelvic heaviness during bouts of impact loading. Many women need 3–6 months for a comfortable running return.
4. Months 6–12: Progressive return to pre-pregnancy training. Re-introduce heavier compound lifts gradually with attention to breath mechanics and pelvic-floor cueing.

The Bø IOC postpartum review explicitly notes that recreational and elite athletes need individualised return programs; cookie-cutter protocols don’t work, especially after caesarean delivery Bø 2017.

Absolute reasons not to do this to aerobic exercise

Per ACOG 2020 and the CSEP 2019 guideline, these conditions warrant not exercising beyond activities of daily living, in consultation with your obstetric provider ACOG 2020 Mottola 2018:

• Ruptured membranes
• Premature labour
• Unexplained persistent vaginal bleeding
• Placenta previa after 28 weeks gestation
• Pre-eclampsia
• Incompetent cervix
• Intrauterine growth restriction
• Multiple gestation (e.g. triplets+) at high risk of preterm labour
• Poorly-controlled type 1 diabetes
• Poorly-controlled hypertension or thyroid disease
• Other serious cardiovascular, respiratory, or systemic disorder

Warning signs — stop exercising

If any of these occur during exercise, stop and contact your obstetric provider:

• Vaginal bleeding
• Regular painful contractions
• Amniotic fluid leakage
• Persistent dyspnoea (shortness of breath) that does not resolve with rest
• Dizziness, headache, chest pain
• Calf pain or swelling (rule out DVT)
• Muscle weakness affecting balance
• Excessive fatigue, palpitations

A practical weekly framework

For a healthy pregnancy without reasons not to do this, with prior exercise experience:

1. 3–5 days of moderate aerobic activity (30 min each): walking, swimming, cycling, prenatal-modified group classes.
2. 2 days of resistance training: full-body, 6–10 sets per muscle group across the week, RPE 6–7 on most sets.
3. Daily pelvic-floor training: 8–12 contractions × 3 sets, plus relaxation patterns. A pelvic-health physio can prescribe individualised work.
4. Mobility & relaxation: prenatal yoga, gentle stretching, breathwork — especially in the third trimester.
5. Listen and adjust: if you’re tired, scale down. The goal is consistency over months, not heroic single sessions.

Beachside note

Beachside’s Mat Pilates and Stretch & Reset classes scale well for pregnancy with coach guidance — let your coach know you’re expecting. Yoga Together is a good fit for partners or a parent-with-toddler return after 12+ weeks postpartum (with clearance). For high-impact classes, the second-trimester window typically requires modifications and the third often calls for a switch to walking + lighter strength. (My family runs the gym; disclosure.)

Common myths

"Don’t let your heart rate go above 140." Outdated. The 1985 ACOG recommendation has been replaced by RPE-based monitoring; healthy pregnant adults can train comfortably at HR 145–160 if their fitness allows.

"Heavy lifting can hurt the baby." Not for healthy pregnancies. Resistance training during pregnancy improves outcomes Perales 2017. Lifts should be modified (no Valsalva, RPE 6–7), but "heavy" doesn’t harm.

"Wait 6 weeks then run." Wrong for most women. The Goom framework typically delays running to 12 weeks pending pelvic-floor function tests Goom 2019. Earlier walking is fine; running needs more time.

"Crunches will fix diastasis." Backwards. Traditional crunches and full sit-ups can worsen diastasis recti. Use horizontal-loading core work instead (bird dog, dead bug, plank with breath cueing).

The bottom line

• Exercise during healthy pregnancy is protective — reducing gestational diabetes, preeclampsia, depression, and excess weight gain meaningfully.
• The target is 150+ minutes per week of moderate-intensity activity, plus resistance training and daily pelvic-floor work.
• Modify, don’t stop — second trimester avoid supine positions, third trimester reduce balance-demand activities, throughout avoid maximal effort.
• Postpartum return is gradual — walking from days 1–3, structured rehab through 6–12 weeks, running typically not before 12 weeks pending function tests.
• Pelvic-health physiotherapy is first-line for any postpartum dysfunction (leakage, heaviness, pain). Don’t accept "it’s normal" without a clinical assessment.
• Listen to red flags — bleeding, persistent dyspnoea, regular contractions, calf pain, dizziness all mean stop and contact your provider.

References