Pregnancy (Prenatal Exercise)

What the current documents say (uncomplicated pregnancy, no contraindications):

• U.S. Physical Activity Guidelines for Americans, 2nd ed. (2018): at least 150 minutes/week of moderate-intensity aerobic activity during pregnancy and the postpartum period, preferably spread through the week. Women who habitually did vigorous aerobic activity or were physically active before pregnancy can continue those activities. Pregnant women should be under the care of a health care provider who can monitor the pregnancy.
• WHO 2020 guidelines: regular activity throughout pregnancy and postpartum; at least 150 min/week of moderate aerobic activity; a variety of aerobic and muscle-strengthening activities (gentle stretching may also help); limit sedentary time. Pelvic-floor muscle training may be done daily to reduce the risk of urinary incontinence.
• ACOG Committee Opinion 804 (2020, reaffirmed 2023): women with uncomplicated pregnancies should be encouraged to do aerobic and strength-conditioning exercise before, during and after pregnancy. ACOG cites the PAGA 150-minute figure and frames the individual goal as moderate-intensity exercise for at least 20–30 minutes per day on most or all days, developed with the patient after a clinical evaluation. Women who were sedentary before pregnancy should progress more gradually.
• Intensity: because heart-rate responses in pregnancy can be blunted or normal, ACOG prefers perceived exertion over heart-rate targets — moderate is about 13–14 ("somewhat hard") on the 6–20 Borg scale — or the talk test (able to hold a conversation). See Talk Test.

Benefits listed in the current documents: ACOG 804 lists less excessive gestational weight gain, gestational diabetes, gestational hypertensive disorders, preterm birth and caesarean birth, and a higher rate of vaginal delivery; WHO 2020 lists reduced risk of pre-eclampsia, gestational hypertension, gestational diabetes, excessive gestational weight gain, delivery complications and postpartum depression, with no increase in stillbirth, newborn complications or adverse effects on birth weight. ACOG notes that concerns about miscarriage, poor fetal growth, musculoskeletal injury or premature delivery have not been substantiated in uncomplicated pregnancies.

Activities ACOG 804 lists as studied and found safe and beneficial: walking, stationary cycling, aerobic exercise, dancing, resistance exercise (weights, elastic bands), stretching, and hydrotherapy/water aerobics. Pelvic-floor training (Pelvic-Floor Considerations in Exercise) fits alongside.

• Lying flat on the back: ACOG 804 advises avoiding long periods lying flat, because after about 20 weeks the uterus can compress the large vessels (aortocaval compression), reducing venous return and causing low blood pressure. WHO 2020 advises avoiding supine activity after the first trimester. Practical upshot: swap prolonged supine work for incline or side-lying versions, and stop if dizzy or nauseous.
• Avoid: contact activities and those with a high risk of abdominal trauma or falling/loss of balance (ACOG 804, WHO 2020); scuba diving (the fetal circulation cannot filter gas bubbles — ACOG 804); activities that limit oxygenation, such as high altitude when not living at altitude (WHO 2020; ACOG notes sea-level residents tolerated activity up to about 6,000 ft).
• Heat and hydration: avoid high heat and humidity, especially in the first trimester; stay well hydrated; prolonged sessions belong in a temperature-controlled environment (ACOG 804, WHO 2020).
• Fuelling: high-intensity or prolonged exercise beyond ~45 minutes can cause low blood sugar, so eat beforehand or shorten/ease the session (ACOG 804).
• Athletes: vigorous exercise into the third trimester appears safe for most healthy pregnancies, but competitive athletes need close supervision; elite athletes should consider lowering resistance loads and avoid overheating (ACOG 804). WHO 2020 advises specialist supervision for anyone exercising well above the guidelines or competing.
• Account for the shifting centre of gravity (progressive lordosis; more than 60% of pregnant women report low-back pain — ACOG 804) → balance caution; water-based exercise is an option when the back hurts.
• Keep diastasis recti and pelvic-floor load in mind (see Diastasis Recti Abdominis, Pelvic-Floor Considerations in Exercise).

• A clinical evaluation should come before an exercise programme; women with medical or obstetric complications need individualised assessment. See Pregnancy Exercise — Contraindications & Warning Signs.
• Warning signs to stop and seek care (ACOG 804, Box 3): vaginal bleeding, abdominal pain, regular painful contractions, amniotic fluid leakage, shortness of breath before exertion, dizziness, headache, chest pain, muscle weakness affecting balance, calf pain or swelling.

• PAGA 2018 and WHO 2020: ≥150 min/week moderate aerobic activity in pregnancy, plus muscle-strengthening (WHO).
• ACOG 804: aerobic and strength exercise encouraged; goal of ≥20–30 min/day moderate on most or all days.
• Gauge intensity by RPE 13–14 or the talk test, not heart-rate targets.
• Avoid: long periods flat on the back (ACOG: after ~20 weeks; WHO: after the first trimester), contact/fall-risk activities, scuba, overheating.
• Stop for: bleeding, abdominal pain, regular painful contractions, fluid leakage, chest pain, dizziness, headache, calf pain/swelling.