Safe Exercises During Pregnancy: ACOG Rules and What to Avoid

For decades, pregnancy and exercise existed in uneasy negotiation. The advice women received ranged from "stay active, it's good for you" to specific rules — maximum heart rate ceilings of 140 or even 120 bpm — that had little scientific support and quietly discouraged many women from staying fit during their pregnancies. The American College of Obstetricians and Gynecologists put that uncertainty to rest in April 2020, when it published Committee Opinion No. 804, its most comprehensive statement on prenatal physical activity to date. What follows is a plain-language guide to what that guidance actually says, what it means trimester by trimester, and which activities genuinely require caution.

What does ACOG actually recommend for exercise in pregnancy?

The core dose in Committee Opinion No. 804 is clear: pregnant women without medical or obstetric complications should aim for 150 minutes of moderate-intensity aerobic activity per week, spread across most days. Both aerobic exercise and strength or resistance conditioning are encouraged throughout pregnancy — this is not a "just walk" recommendation.

The opinion, developed with the assistance of committee members Meredith L. Birsner, MD, and Cynthia Gyamfi-Bannerman, MD, MSc, and published in Obstetrics & Gynecology (2020;135:e178–88), also expanded the documented benefits of prenatal exercise significantly. Regular activity is associated with reduced risk of gestational diabetes mellitus, preeclampsia, cesarean delivery, and operative vaginal delivery. Postpartum recovery is faster among women who stayed active, and there is a protective effect against postpartum depressive disorders. Crucially, the same opinion stated that "bed rest is not effective for the prevention of preterm birth and should not be routinely recommended" — a direct reversal of the clinical conservatism that had been quietly prevailing for years.

The 150-minute weekly target can be divided however fits your schedule. Thirty minutes on five days is the obvious structure, but bouts of at least 10 minutes count toward the total. Many women in the first trimester find that shorter, more frequent sessions are more manageable when fatigue and nausea are at their peak.

Why the heart-rate ceiling was wrong — and what to use instead

The 140-bpm maximum (sometimes cited as 120 bpm) was not derived from clinical trials. It emerged from an era when exercise in pregnancy was viewed with general caution and when the physiological changes of pregnancy on cardiovascular response were poorly understood. More than half of obstetricians — 54%, according to a study published in PubMed Central — still recommend heart-rate limits to their patients, representing a significant gap between what the best evidence supports and what many women are actually told.

ACOG's replacement guidance endorses two tools that are both simpler and more accurate.

The first is the talk test: moderate-intensity exercise is effort at which you can speak in full sentences but cannot sing. If you cannot carry on a brief conversation, slow down. If you can sing comfortably, you can push a little harder. This test automatically adjusts for individual variation in cardiovascular fitness, altitude, ambient temperature, and gestational age — all factors that make a fixed bpm ceiling meaningless.

The second is the rating of perceived exertion (RPE) scale, typically the Borg 6–20 scale. A target of roughly 12–14 on the Borg scale corresponds to moderate exertion and aligns with the talk-test zone. Women who exercised intensively before pregnancy, including competitive athletes, may continue vigorous-intensity activity with their provider's individualized guidance — there is no universal obligation to dial down to moderate.

Which exercises are safe — and which require caution — by trimester?

Most exercise types are safe throughout pregnancy in uncomplicated cases. Walking, swimming, stationary cycling, low-impact aerobics, yoga (with modifications), Pilates (with modifications), resistance training with appropriate loads, and jogging for women who ran before pregnancy are all consistent with ACOG guidance. The modifications that matter are specific to trimester.

First trimester. Overheating risk is highest in early pregnancy, when organ formation is underway. Keep core temperature moderate through clothing choice, adequate hydration, and avoiding hot or humid environments — this is also why hot yoga and hot Pilates are contraindicated throughout pregnancy. Standard prenatal programs like The Bloom Method and Sweat's "Pregnancy with Kayla Itsines" both organize first-trimester programming around foundational core work and cardiovascular maintenance rather than intensity increases.

Second trimester. The center of gravity begins shifting noticeably, which affects balance during activities that seemed perfectly stable before. Activities with fall risk — trail running on uneven surfaces, outdoor cycling, step aerobics with lateral movement — become mechanically riskier even if they were previously comfortable. By mid-second trimester, prolonged supine (flat-on-your-back) positions should be minimized: the growing uterus can compress the inferior vena cava, the large vein returning blood to the heart, reducing venous return and dropping both maternal blood pressure and fetal oxygen delivery.

Third trimester. Impact typically warrants reduction, and recovery time between sessions lengthens. Women with a history of preterm labor or fetal growth restriction should reduce activity in the second and third trimesters per their provider's direction. Many women shift from running to walking, swimming, or stationary cycling in the final weeks — not because activity is dangerous, but because comfort and balance have changed enough to make lower-impact choices more practical.

The activities ACOG identifies as off-limits throughout pregnancy

Regardless of fitness level or trimester, ACOG identifies four categories of activity to avoid:

Activities to avoid during pregnancy per ACOG

Activity category	Specific examples	Primary risk
Contact sports	Ice hockey, boxing, martial arts, competitive basketball	Abdominal trauma
High fall-risk activities	Downhill skiing, off-road cycling, gymnastics, horseback riding	Fall with abdominal impact
Scuba diving	All open-circuit and closed-circuit scuba	Fetal decompression injury
High-altitude exercise	Exercise above 2,500 m (8,200 ft) for non-altitude residents	Reduced fetal oxygen availability

Beyond these four, supine exercise after the first trimester and prolonged motionless standing both carry the same hemodynamic concern: compression of the inferior vena cava by the gravid uterus.

Absolute contraindications: when exercise should not happen at all

For most healthy, uncomplicated pregnancies, the question is not whether to exercise but how. However, certain medical conditions make exercise contraindicated entirely. Per Committee Opinion 804, absolute contraindications include: hemodynamically significant heart disease; restrictive lung disease; incompetent cervix or cerclage; persistent second- or third-trimester bleeding; placenta previa after 26 weeks; ruptured membranes; preeclampsia or pregnancy-induced hypertension; and severe anemia.

Relative contraindications — conditions that require a clear provider conversation before continuing exercise, not an automatic halt — include severe obesity, extreme underweight, poorly controlled Type 1 diabetes, hypertension, and poorly controlled thyroid disease, among others. If you have a high-risk diagnosis of any kind, always seek individualized clearance before starting or resuming a program.

This article provides general information, not individualized medical advice. Your obstetric provider is the right person to evaluate your specific risk profile and clear you for exercise.

The nine warning signs to stop exercising immediately

ACOG specifies nine clinical signals that mean stop the session and contact your provider:

1. Vaginal bleeding
2. Regular or painful contractions
3. Amniotic fluid leakage
4. Shortness of breath before exertion begins
5. Dizziness or feeling faint
6. Headache
7. Chest pain
8. Calf pain or swelling (possible deep vein thrombosis)
9. Decreased fetal movement

Nausea, extreme fatigue, and sudden muscle weakness during a session are additional subjective signals to stop. Do not push through any of these symptoms. The list applies across all trimesters and all activity types — walking and water aerobics are not immune.

One underappreciated foundation: nutritional support for exercise capacity

Standard prenatal exercise guidance rarely addresses nutrition — but for many women, the limiting factor in their exercise capacity is not programming; it is nutritional status. A few specifics are worth knowing.

Magnesium and leg cramps. Leg cramps are among the most common reasons pregnant women scale back exercise in the second and third trimesters. They are associated with low magnesium, and approximately half of the participants in one Brazilian controlled trial had serum magnesium below 1.8 mg/dL at enrollment. A 2021 review of 188 prenatal supplements found that 66% included magnesium but at a median of only 50 mg per serving — far below the 310–360 mg daily adequate intake for pregnant women. Magnesium glycinate is generally better tolerated than magnesium oxide. Discuss any supplementation change with your provider; the tolerable upper intake limit from supplements is 350 mg/day.

Vitamin D and pelvic floor strength. A 2023 cross-sectional study of 250 pregnant women beyond 28 weeks found that 84% were vitamin D-deficient, and women in the deficient group had significantly higher rates of urinary incontinence and meaningfully lower postpartum pelvic floor muscle strength. Pelvic floor muscles express vitamin D receptors — the link appears to be direct, not merely correlational. Integrative practitioners typically target a serum 25-OH-D level of 40–60 ng/mL; work with your provider on testing and dosing.

These are roots worth addressing. A well-built exercise program delivers far more when the body's basic nutritional terrain is solid underneath it.