Pregnancy and the first year after birth
Keep training once the obstetric team agrees, let effort and the talk test set the ceiling (no heart-rate number is a law) and keep heat inside what was tested; after birth no running before 3 weeks, then return on a screen and symptoms, never a date; pelvic-floor training at any age; warning signs go to a clinician
The question it answers
A woman who trains is pregnant, has given birth in the past year, or leaks urine when she runs or jumps.
Does she keep training, change it or stop; how hard may she go and how does she judge it; what about heat, the gym and falls; when and how does she come back after the birth; what does breastfeeding change; what helps leaking and an abdominal gap; and what goes to a clinician?
Short answer: once the obstetric team has cleared her, keep training and let effort and the talk test set the ceiling; keep heat inside the tested conditions; after birth, nothing that runs before 3 weeks, then a screened, person-specific return with the pelvic floor and strength first; ask about leaking at any age and send the programme to a pelvic-health physiotherapist.
The assistant never diagnoses, never judges a contraindication, never gives a heart-rate number as a rule and never promises a return date.
What this guide owns and what it leaves
| Owns (decided here) | Leaves to |
|---|---|
| Training through pregnancy: continue, modify or stop; intensity and how to judge it; heat, gym, falls; the warning signs | The menstrual cycle and hormonal contraception → SYNTH-37; perimenopause and after → SYNTH-96 |
| The return after birth: readiness, timeline, pelvic floor, abdominal gap, breastfeeding and fuelling, sleep | The REDs screen and stop rules → SYNTH-54; bone-like pain and running injuries → SYNTH-94 and SYNTH-73; a return after other breaks → SYNTH-36 |
| Leaking and the pelvic floor at any age | Heat acclimation and altitude outside pregnancy → SYNTH-04, SYNTH-06; supplements, including in pregnancy → SYNTH-67; strength programming → SYNTH-43, SYNTH-44; saddle-area symptoms on the bike → SYNTH-92 |
Default — the decision, in order (what to prescribe first)
Not from a study; the base's own practice for the order, the effort governor and every step not given a source:
Clearance and warning signs first. In pregnancy the obstetric team clears training and rules out contraindications; any warning sign below stops the session and goes to them (REF-567, A; its contraindication and warning-sign lists are from the full text, not checked against the abstract). The assistant never judges a contraindication.
Cleared and uncomplicated: keep training, aerobic and strength. Exercise in such a pregnancy is "safe and desirable", and women who were vigorously active before pregnancy can continue (REF-567, A); the Canadian guideline found moderate benefits and no harms, and its full text sets at least 150 min of moderate activity a week over at least 3 days with aerobic and resistance work (REF-568, A) — a public-health floor, not an athlete's ceiling (practice).
Do not tell a healthy athlete to drop vigorous work only because she is pregnant: vigorous exercise kept up into the third trimester showed no evidence of a difference in birth weight or small-for-gestational-age risk (REF-1396, A-), and women who competed at elite level just before conceiving had birth and delivery outcomes like other women's (REF-1395, B+).
Effort and the talk test set the ceiling, not a heart-rate number (practice). The 90%-of-maximum line is usually traced to six Olympic athletes tested once on three to five treadmill workloads (REF-1400, B-); 1-min reps peaking near 96% caused no fetal bradycardia before or right after the session in 15 women (REF-1401, B).
Ease long near-maximal efforts late in pregnancy (practice: longer efforts above 90% are untested, and REF-1400's stage durations are not in its abstract) and use any limit the obstetric team gives.
Let comfort set the volume as pregnancy advances (practice; no entry in the base measures how athletes' volume should fall). Keep the strength work, and swap lying on the back for incline or side-lying positions if it brings light-headedness, nausea or feeling unwell (REF-568, full text).
Heat inside what was tested. Up to 35 min of exercise at 80-90% of maximum heart rate in 25 °C and 45% humidity, 45 min of exercise in water of 33.4 °C or less, or 20 min in a 40 °C bath or a 70 °C dry sauna kept every woman under 39.0 °C (REF-1403, B+).
Hotter, more humid, longer or repeated exposures were not tested — not shown harmful, not shown safe — so no heat-acclimation block, post-training sauna, hot race plan or altitude camp comes from the base in pregnancy; those go to the obstetric team (practice).
After birth: no running before 3 weeks, then a screen, not a date. The panel agreed on no running before 3 weeks, a fully healed birth injury and a person-specific timeline, with readiness screened — walking 30 min and impact tasks such as jogging on the spot and hopping without leaking, heaviness or pain, plus sleep, mood, fatigue, eating and feeding (REF-1397, B, consensus).
The plan after that is relative rest, then walk-run, then gradual increases in duration and intensity with strength training (REF-569, B); duration before intensity is the base's practice (REF-569 gives no order). Elite or symptomatic runners see a clinician or a pelvic-health physiotherapist before the first run (REF-1397).
The pelvic floor from pregnancy on. Daily pelvic-floor training appears in the Canadian pregnancy guideline's full text (REF-568); after birth it lowered the odds of leaking by 37% (REF-1398, A-), and in athletes it reduced leakage (REF-728, A-). The programme belongs to a pelvic-health physiotherapist (REF-728; practice).
Breastfeeding: eat to cover it; no deficit now. Aerobic training left milk volume, composition and the baby's weight gain unchanged in 33 sedentary women who ate more (REF-570, B+); a deficit while breastfeeding was not tested there, and for a training athlete the base's practice is none, with the REDs screen first (SYNTH-54).
Promise nothing — no safe heart rate, no safe heat dose beyond the tested ones, no return date. Bone-like pain on the way back means no running and a clinician (SYNTH-94).
When to stop and see a clinician
None of these is a diagnosis; each means stop the session and see the obstetric team, a doctor or a pelvic-health physiotherapist:
Decision table by stage
"(practice)" marks a call that is not from a study; the base's own practice. Every number carries its entry.
| Stage or question | Keep doing | Change | Untested or avoid | Ask | Refer |
|---|---|---|---|---|---|
| Early pregnancy (first trimester) | Normal training, aerobic and strength, once cleared (REF-567, A) | Fuel to need and to nausea; easier days when sick or exhausted (practice) | The least-studied stage: no pooled data for vigorous exercise in the first or second trimester alone, and one cohort described in REF-1396 (not pooled) linked daily vigorous exercise in the first 15 weeks with three-fold the risk of a small-for-gestational-age baby — hard sessions on some days, not every day (practice); heat blocks and altitude camps (practice; REF-1403 tested short exposures only) | Nausea, fatigue, bleeding, pain | Any warning sign (REF-567) |
| Second and third trimesters | Aerobic and resistance work; vigorous work (mostly 70-90% of maximum heart rate) into the third trimester showed no evidence of a difference in birth weight (+8.06 g, 95% CI −57.44 to 73.55; 8,006 infants) or in small-for-gestational-age risk (REF-1396, A-, low-risk non-athletes); short intervals were tolerated in one session (REF-1401, B) | Effort and the talk test govern; volume and pace fall as comfort dictates; long near-maximal efforts eased late on (all practice) | Sustained efforts above about 90% of maximum: untested, not shown harmful — REF-1396's authors advise avoiding any effort at 90% or more until shown safe; races and hot-humid long sessions (untested, REF-1403) | Dizziness, contractions, fluid leakage, calf pain, leaking urine | Warning signs (REF-567); a baby measuring small → the obstetric team (REF-1396's authors suggest moderate rather than vigorous work then — their caution, not a tested rule) |
| A hot day, a sauna or a heat block while pregnant | Within what was tested: up to 35 min at 80-90% of maximum heart rate in 25 °C and 45% humidity; water exercise at 33.4 °C or less for up to 45 min; a 40 °C bath or a 70 °C, 15% humidity sauna for up to 20 min — highest individual core temperature 38.9 °C, none at 39.0 °C (REF-1403, B+, abstract) | Hot days: cooler hours, indoors with a fan, shorter (practice) | Heat-acclimation blocks, overdressing, sauna straight after training (the 15-30 min post-training sauna of SYNTH-04 can run past the longest tested sauna, 20 min, and adds heat on top of exercise), races in heat, multi-day exposure — untested (practice: not prescribed); altitude camps — no entry in the base | Any hot race or heat plan | The obstetric team for any heat or altitude plan (practice) |
| Gym day: lying on the back, heavy lifts, falls | Resistance training (REF-568, A; full text) | Supine work swapped for incline or side-lying if it brings light-headedness, nausea or feeling unwell (REF-568, full text); a review not in the base (Mottola 2019) found insufficient evidence either way on supine exercise | Heavy lifting and breath-holding: no entry in the base — loads she knows, no new maximal attempts (practice); contact sport, fall-prone trails and fast descents: no study — lower-risk options such as the indoor trainer as balance changes (practice) | Light-headedness lying flat, leaking, pelvic or back pain | Pelvic or back pain that persists → a physiotherapist (practice) |
| 0-3 weeks after birth | Walking as comfortable; pelvic-floor training — after birth it lowered the odds of leaking, and the effect did not differ by whether it started before or after 12 weeks (REF-1398, A-) | Sleep, feeding and recovery come first (REF-569: the modifiers it names) | Running and impact: not before 3 weeks (85.5% of the panel; REF-1397, B) | Bleeding, the wound or tear, mood, sleep | Lochia, a birth complication, chest or calf pain, low mood (REF-1397; practice) |
| From 3 weeks: the first run | Strength, the pelvic floor and walking; walk-run once screened (REF-569, B; REF-1397, B) | A person-specific timeline: birth injury fully healed (97.6%); walking 30 min (97.7%), jogging on the spot for 1 min (98.8%), hops and single-leg tasks without leaking, heaviness or pain (REF-1397); duration before intensity (practice) | A date-driven return; a weight-loss deficit (practice; REF-570 did not test one) | Leaking, heaviness or a bulge, pelvic or back pain, sleep, mood, eating, feeding | Elite or symptomatic runners → a clinician or a pelvic-health physiotherapist before the first run (REF-1397) |
| 3-12 months: back to full training and racing | Build back to normal training; performance can return — 101 elite athletes (40.5% of those reporting) improved after pregnancy (REF-1402, B+, very low certainty, counts) | Volume before intensity, one step at a time, each held while symptom-free (practice; SYNTH-36); racing once training is symptom-free (practice) | A fast impact ramp while under-eating (inference from REF-1402's stress fractures and the triad factors that add up in REF-1392, B) | Bone pain, energy, hunger, periods once breastfeeding ends | Bone-like pain → no running, a clinician (SYNTH-94); no periods after weaning → a doctor (REF-1399) |
| Breastfeeding | Aerobic training: milk volume, composition, prolactin and the baby's weight gain unchanged in 12 weeks at 60-70% of heart-rate reserve, 45 min, 5 days a week (REF-570, B+, 33 sedentary women) | Eat to cover feeding and training: the exercisers ate about 330 kcal a day more and covered the roughly 400 kcal a day the sessions cost (REF-570) | A deficit — untested there, and for a training athlete not now (practice; SYNTH-54) | Milk-supply worries, hunger, fatigue, sleep | The REDs screen (SYNTH-54); a dietitian for a weight goal (practice) |
| Leaking on runs, jumps or hard efforts, at any age | Running; pelvic-floor training reduced leakage in athletes (SMD −1.13, 95% CI −1.84 to −0.41; REF-728, A-) and lowered its odds after birth (REF-1398, A-) | Ask at a rise in weekly hours as well as at a move to more impact: each extra weekly hour went with 6% higher odds (OR 1.06, 1.01-1.11) while the impact category did not explain leakage (low vs high impact OR 0.93, 0.45-1.95) (REF-1408, A-, a between-study association, mostly nulliparous); asking at a rise in hours is the base's inference and practice | Quitting impact by default; treating it as rare — 39% of adult women athletes reported leakage (REF-1408) | "Does anything leak on hard efforts, jumps or coughs?" (practice, REF-727) | A pelvic-health physiotherapist for the diagnosis and the programme (REF-727, REF-728) |
| A gap between the abdominal muscles (diastasis) | Core and abdominal training: it narrowed the gap by about 0.35-0.52 cm on a starting gap near 2.4 cm (low to moderate certainty; REF-1398, A-) | Nothing by the gap alone: the panel did not agree on it as a return-to-running milestone (55.3%) or on a 3-finger gap with doming as a reason to stop running (28.2%) (REF-1397) | Promising that transversus work closes it — a transversus contraction widened the gap acutely (REF-1398) | Doming, pain, a bulge | A pelvic-health physiotherapist; a bulge or a hernia → a clinician (practice) |
Key Findings — what the evidence shows
Training in a healthy pregnancy is endorsed. Safe and desirable without contraindications, and previously vigorous exercisers can continue (REF-567, A, a committee opinion on largely observational evidence); moderate benefits and no harms identified, with at least 150 min of moderate activity a week in the full text (REF-568, A).
Vigorous work into the third trimester did not change growth. In a review of 5 RCTs (623 women) and 10 observational studies (32,080), birth weight, pooled from 12 studies of 8,006 infants, differed by +8.06 g (95% CI −57.44 to 73.55), small-for-gestational-age and low-birth-weight risk showed no evidence of a difference, and gestation was 0.21 weeks longer (0.15 to 0.27); most of the exercise was below 90% of maximum heart rate, and the first trimester could not be analysed (REF-1396, A-, mostly observational, low-risk women).
Elite athletes' pregnancies were like other women's. In 11 studies (2,256 women), no evidence of a difference in birth weight, preterm birth, caesarean or labour (no effect sizes or CIs for these in the abstract); less pregnancy low back pain (OR 0.38, 0.20-0.73; low certainty) and more excessive weight gain (OR 2.47, 1.26-4.85; very low); three episodes of fetal bradycardia in 7 women after high-intensity exercise, all resolved within 10 min of stopping — most likely REF-1400's six athletes plus one case report, so not independent of it (REF-1395, B+, abstract; the exposure is elite status before pregnancy, not a measured dose).
The 90% line is one small observation. In six Olympic endurance athletes at 23-29 weeks, each tested once on three to five treadmill workloads at about 60-90% of VO2max, the fetal heart rate stayed normal while the mother ran below 90% of her maximum, and bradycardia with a high umbilical pulsatility index appeared above 90% when uterine blood flow fell under half its starting value; both normalised quickly on stopping (REF-1400, B-, abstract).
In 15 women at 27.3 ± 3.5 weeks, ten 1-min reps (peak 96 ± 5% of maximum, range 87-105%) and 30 min at 64-76% both left the fetal heart rate higher afterwards (+14 ± 7 and +10 ± 10 bpm) with no bradycardia and umbilical indices in the normal range — measured before and after, not during, the reps (REF-1401, B, abstract).
Heat: the tested conditions stayed under 39 °C. In 12 studies (347 women), the highest mean end-trial core temperature was 38.3 °C (95% CI 37.7-38.9) on land, 37.5 °C in water, 36.9 °C in a hot bath and 37.6 °C in a sauna; the highest single value was 38.9 °C (REF-1403, B+, abstract; core temperature, not fetal outcomes).
After birth, readiness is screened, not timed. In a three-round Delphi (118 → 107 → 95 professionals, consensus at 75%), no running before 3 weeks, a healed birth injury and a person-specific timeline were agreed, a return before 12 weeks was agreed to be possible, and no cut-offs were set (REF-1397, B, expert opinion); the plan is relative rest, walk-run and gradual progression with strength (REF-569, B).
The 2025 Canadian guideline, built on 7 systematic reviews, judges that following its recommendations is likely to bring large improvements in well-being, pelvic, musculoskeletal and cardiometabolic health and less fatigue without adverse events (moderate certainty); its recommendations are not in the base (REF-1394, A, abstract).
Elite athletes come back early, and some come back injured. They returned before 6 weeks more often than non-elite women (OR 6.93, 95% CI 2.73-17.63; 145 women); 14 elite athletes were injured after birth, 7 of them with stress fractures (3 studies, 179 women); all very low certainty, with no comparison group for injury (REF-1402, B+, abstract).
The pelvic floor is trainable, and leaking is common. After birth, pelvic-floor training lowered the odds of urinary incontinence by 37% (OR 0.63, 0.41-0.97; 7 RCTs, 1,930 women; moderate) but showed no evidence of a difference in severity (SMD −0.04, −0.49 to 0.42); its 56% lower odds of prolapse rest on one trial of 123 women after an episiotomy or second-degree tear, and two pooled trials showed no difference (REF-1398, A-).
In athletes, it reduced leakage (REF-728, A-). Of 4,649 adult women athletes, 39% (95% CI 33-46) reported leakage, 34% in nulliparous-only samples; sport and impact category did not explain the spread between cohorts, and cohorts training more hours a week leaked a little more (a between-study association; REF-1408, A-).
Women who cycle reported no more urinary symptoms than swimmers or runners (REF-1269, B+).
Breastfeeding and training are compatible when food covers both. In 33 sedentary breastfeeding women, 12 weeks of aerobic training raised VO2max 25% against 5% with no difference in milk volume or composition, the baby's weight gain or prolactin; the exercisers ate more (REF-570, B+).
It does not show: a safe or unsafe heart rate for anyone; that longer near-maximal efforts, elite training volumes or repeated sessions above 90% are safe in pregnancy; anything about altitude, heavy lifting, breath-holding or falls in pregnancy; fetal outcomes of heat; a tested return-to-running protocol or any screen's ability to predict injury or symptoms; whether an early return causes stress fractures; anything about high-volume training while breastfeeding, lactation and bone, or a deficit in a breastfeeding athlete.
Conflicts and how they are resolved
Practical Application — how the assistant says it
What NOT to do
Evidence gaps
Limitations
How this entry was checked and changed
(the pregnancy half rests on two A guidelines, REF-567 and REF-568, whose dose and warning-sign lists are full text, an A- meta-analysis of vigorous exercise into the third trimester REF-1396, and B+ reviews of heat exposures REF-1403 and of elite athletes REF-1395; the pelvic floor on two A- meta-analyses REF-1398 REF-728 and an A- prevalence review REF-1408. Held at B, not higher, because the return after birth rests on one B Delphi reported in two papers REF-1397 REF-569 while the 2025 guideline's recommendations are not in the base REF-1394, the heart-rate evidence is a B- case series and a B single-session crossover REF-1400 REF-1401, breastfeeding has one B+ trial in sedentary women REF-570, and the effort governor, the volume changes, the progression steps, the gym and fall rules and the fuelling line are the base's practice)