Exercise during pregnancy: benefits and limits

A 31-year-old woman, in the 14th week of her first pregnancy, comes to her prenatal visit with a direct question. Before getting pregnant, she ran three times a week and did weight training. Since the positive test, she stopped everything, because she heard from her family that exercise "can make the baby come out". Now she wants to know whether she can go back, what she can do, until when, and what should make her stop.

The short answer is that, for most pregnant women, exercise is safe and brings benefits. The 2020 World Health Organization guideline recommends that pregnant and postpartum women without contraindication do at least 150 minutes per week of moderate aerobic activity (Bull, 2020). The complete answer, however, requires two checks that take only a few minutes: looking for contraindications and teaching the stop signs.

This text goes through what happens in the pregnant woman's body during exercise, the benefits for the mother and the baby, who should not exercise, the signs that call for stopping the activity, and how to give guidance in practice, including very active pregnant women and athletes.

Key points

• The WHO recommends at least 150 minutes per week of moderate aerobic activity for pregnant women without contraindication, along with muscle strengthening (Bull, 2020).
• In clinical trials, physical activity during pregnancy was associated with less gestational diabetes (odds ratio 0.60) and fewer hypertensive disorders (odds ratio 0.66) (Teede, 2022).
• Exercise did not increase the risk of low birth weight or of a newborn small for gestational age in a meta-analysis of 63 trials (Zhang, 2023).
• Gestational hypertension, preeclampsia, rupture of membranes, placenta previa and preterm labor are among the absolute contraindications (Hinman, 2015).
• Vaginal bleeding, dizziness, chest pain, loss of fluid and regular, painful contractions mean stopping right away (Davenport and Hayman, 2022).
• Fetal heart rate decelerations appeared only with acute maximal effort, above 90 of every 100 beats of the maternal maximum heart rate (Wieloch, 2022).

Summary

• Why talk about exercise in pregnancy
• The benefits for the mother
• What happens to the baby
• Who should not exercise: the contraindications
• The stop signs
• Intensity, athletes and special situations
• How to give guidance in practice
• How NEXO helps train this reasoning
• Frequently asked questions
• Take-home messages

Why talk about exercise in pregnancy

The patient's question is common, and the answer she gets is often vague. For a long time, pregnancy was seen as a period of rest, and the standard guidance was to "take it easy". This culture leaves a mark: only 10 to 15 of every 100 pregnant women reach the physical activity recommendation (Newton and May, 2017).

Two failures that add up

Newton and May point to two sources of this gap between recommendation and practice (Newton and May, 2017). The first is in the patient and the culture she lives in, with beliefs about the risk of miscarriage or of "hurting the baby" (Newton and May, 2017). The second is in the professional who does not recommend exercise for lack of knowledge or motivation (Newton and May, 2017).

The second failure is the one the clinician can correct at the very next visit. It depends on understanding what happens in the pregnant woman's body, knowing the real contraindications and being able to explain the warning signs in a concrete way.

What changes in the pregnant woman's body

Pregnancy changes physiology at rest, and these changes explain much of the recommendations. Uterine blood flow increases about tenfold by term, going from 2 to 17 of every 100 parts of cardiac output, between 500 and 800 mL per minute (Newton and May, 2017). About 80 of every 100 parts of this flow go to the interface between the mother and the placenta (Newton and May, 2017).

Cardiac output, hemoglobin, oxygen and carbon dioxide pressures and maternal pH determine the oxygen supply to the fetus (Newton and May, 2017). During moderate exercise, the body redistributes blood to the muscles, and the historical doubt was whether this would leave the fetus short of oxygen. The physiological studies reviewed by Newton and May showed that, in healthy pregnant women, moderate exercise and even vigorous treadmill exercise late in pregnancy ended with normal deliveries and normal newborns (Newton and May, 2017).

Heat and position

Dissipating heat during exercise is important to keep hyperthermia from increasing fetal oxygen consumption (Newton and May, 2017). So the practical guidance is to avoid excessive heat and high humidity, such as hot-room yoga, and to prefer cooler times of day or air-conditioned settings (Davenport and Hayman, 2022). The text on heat illness reviews the spectrum of hyperthermia in adults.

Position also matters. The recommendations summarized by Hinman and colleagues call for avoiding lying face up after the first trimester and long periods standing still (Hinman, 2015).

The benefits for the mother

The WHO guideline summarizes what the evidence showed for the mother: lower risk of pre-eclampsia, gestational hypertension, gestational diabetes, excessive weight gain, delivery complications and postpartum depression (Bull, 2020). The most recent reviews detail the size of these effects.

Gestational diabetes and hypertensive disorders

The meta-analysis by Teede and colleagues pooled 117 clinical trials with 34,546 pregnant women that tested diet, physical activity or both (Teede, 2022). Physical activity interventions were associated with less gestational diabetes, with an odds ratio of 0.60, and with fewer hypertensive disorders of pregnancy, with an odds ratio of 0.66 (Teede, 2022). Taken together, lifestyle interventions reduced gestational weight gain by 1.15 kg on average (Teede, 2022).

The umbrella review by Martínez-Vizcaíno and colleagues added details on when the effect appears (Martínez-Vizcaíno, 2023). For gestational diabetes, the reduction was greater when exercise began in the first trimester (odds ratio 0.55) and when it was supervised (odds ratio 0.60) (Martínez-Vizcaíno, 2023). Pre-eclampsia only decreased when exercise began in the first trimester, with an odds ratio of 0.34 (Martínez-Vizcaíno, 2023).

Davenport and Hayman summarize the body of evidence: prenatal exercise reduced the odds of depression, pre-eclampsia and gestational diabetes by between 40 and 67 per 100, without increasing miscarriage, preterm birth or a baby small for gestational age (Davenport and Hayman, 2022). Those who treat hypertensive patients outside pregnancy can compare this with what exercise does to blood pressure in general.

Delivery

In the review by Zhang and colleagues on the type and duration of delivery, with 57 trials, physical activity reduced cesarean delivery, with a relative risk of 0.87 (Zhang, 2023). Instrumental delivery also decreased, with a relative risk of 0.84, and the first stage of labor was about 62 minutes shorter (Zhang, 2023). In the meta-analysis by Teede, physical activity was associated with fewer cesarean deliveries, with an odds ratio of 0.85 (Teede, 2022).

Pelvic floor

Pelvic floor muscle training deserves its own highlight. In a review of 30 studies with 6,691 pregnant women, this training reduced urinary incontinence, with a relative risk of 0.72 (Zhang, 2024). Third- and fourth-degree perineal tears also decreased, with a relative risk of 0.50, although episiotomy did not change (Zhang, 2024).

Mental health

Prenatal depression is common and often goes undiagnosed. In the meta-analysis by Sánchez-Polán and colleagues, with 15 trials, exercise reduced prenatal depression scores, with an effect size of -0.36 (Sánchez-Polán, 2021). The risk of prenatal depression also fell, with a relative risk of 0.84 (Sánchez-Polán, 2021). The text on exercise in depression discusses type and intensity outside pregnancy.

What happens to the baby

The pregnant woman's most common concern is the baby, and this is where a clear explanation makes the most difference.

Birth weight

In a meta-analysis of 63 trials with 16,524 pregnant women, physical activity reduced macrosomia, with a relative risk of 0.79 (Zhang, 2023). At the same time, it did not change the risk of low birth weight or of a newborn small for gestational age (Zhang, 2023). The WHO also notes that physical activity in pregnancy did not increase stillbirth, neonatal complications or adverse effects on birth weight (Bull, 2020).

Prematurity

Wen and colleagues' meta-analysis analyzed observational and intervention studies on physical activity outside work (Wen, 2017). In the cohorts, leisure-time physical activity was associated with fewer preterm births, with a relative risk of 0.83 (Wen, 2017). In the intervention trials, the effect on prematurity was not significant, which rules out the fear that exercise triggers labor before term (Wen, 2017).

Fetal heart

Fetal heart rate and its variability are the parameters most used to assess fetal well-being during maternal exercise (Bauer, 2020). These measures reflect the fetal autonomic nervous system, which responds quickly to the environment (Bauer, 2020). At moderate effort, the changes are slight and transient; the question of maximal effort appears later, in the section on athletes.

Who should not exercise: the contraindications

The WHO guideline directs the recommendation to pregnant women "without contraindication" (Bull, 2020). The first task of the consultation is therefore to look for them. Hinman and colleagues note that healthy women without contraindication are considered low risk, regardless of their previous activity level (Hinman, 2015).

Absolute and relative

The table gathers the contraindications described in the clinical review by Hinman and colleagues, which follows the recommendations of the American college of obstetricians (Hinman, 2015).

Type	Condition	What to do
Absolute	Gestational hypertension and pre-eclampsia (Hinman, 2015)	Stop structured exercise and keep daily activities
Absolute	Rupture of membranes and preterm labor (Hinman, 2015)	Stop and assess the pregnant woman in an obstetric service
Absolute	Cervical incompetence (Hinman, 2015)	Stop structured exercise
Absolute	Bleeding in the second or third trimester and placenta previa (Hinman, 2015)	Stop and investigate the cause
Absolute	Multiple pregnancy with risk of preterm birth (Hinman, 2015)	Stop structured exercise
Relative	Intrauterine growth restriction (Hinman, 2015)	Decide case by case with the obstetrician
Relative	Extremes of weight (Hinman, 2015)	Adjust type and intensity
Relative	Poorly controlled diseases: type 1 diabetes, hypertension, epilepsy, thyroid disease (Hinman, 2015)	Control the disease and individualize

Contraindication is not bed rest

Having an absolute contraindication does not mean staying in bed. Davenport and Hayman stress that even these pregnant women are encouraged to keep their activities of daily living, because bed rest is not endorsed by obstetric societies, has potential for harm and no demonstrated benefit (Davenport and Hayman, 2022). This is a good example of quaternary prevention: protecting the patient from an intervention that seems prudent but does harm.

Chronic diseases

Women with cardiovascular, respiratory or systemic diseases, or with relative contraindications, are considered high risk and need individual assessment before starting (Hinman, 2015). For screening, Davenport and Hayman cite the Get Active Questionnaire for Pregnancy, which the pregnant woman can fill in herself and which identifies the minority who need additional assessment (Davenport and Hayman, 2022).

Activities to avoid

Some activities are out even in an uncomplicated pregnancy. Sports with a high risk of contact, falling or abdominal trauma, such as horse riding, alpine skiing and cycling other than on a stationary bike, should be avoided (Davenport and Hayman, 2022). Scuba diving is also off the list, because of the risk to the fetus (Hinman, 2015). Exercise above 5,250 feet, about 1,600 meters, is not recommended for those who live near sea level (Hinman, 2015). Excessive heat and high humidity, as in hot-room yoga, increase the risk of dehydration and hyperthermia (Davenport and Hayman, 2022).

Direct abdominal trauma can cause loss of amniotic fluid, placental abruption or preterm labor, despite the protection of the uterus and the fluid (Davenport and Hayman, 2022).

The warning signs to stop

This is the central point of the consultation: the pregnant woman needs to leave knowing exactly what should make her stop and seek care. The signs described in the reviews overlap considerably.

What means stopping right away

Hinman and colleagues list the signs and symptoms that mean stopping the exercise (Hinman, 2015):

• vaginal bleeding (Hinman, 2015);
• dizziness (Hinman, 2015);
• calf pain or swelling (Hinman, 2015);
• chest pain (Hinman, 2015);
• signs of preterm labor (Hinman, 2015);
• decreased fetal movements (Hinman, 2015);
• loss of amniotic fluid (Hinman, 2015);
• shortness of breath even before exertion (Hinman, 2015).

Davenport and Hayman add a description of each sign as a "red flag": excessive and persistent shortness of breath, severe chest pain, regular and painful uterine contractions, vaginal bleeding, persistent loss of fluid from the vagina, and dizziness or a feeling of faintness that does not improve with rest (Davenport and Hayman, 2022).

Why each sign matters

These signs may represent the start of labor or the symptom of a clinically relevant complication (Davenport and Hayman, 2022). Calf pain and swelling suggest deep vein thrombosis. Chest pain and disproportionate shortness of breath call for cardiac and pulmonary assessment, and the text on heart attack in women shows how symptoms are underestimated. Dizziness that does not pass or fainting requires the same logic as syncope in the emergency department: separating the benign from the dangerous.

How to teach the signs

Generic guidance ("stop if you feel something strange") almost never works. The text on safety net at the consultation shows why specific guidance, with the sign, what to do and where to go, protects more than vague guidance. In pregnancy, this means naming each sign, saying that the activity must stop immediately and indicating where to seek help.

It is also worth reminding the pregnant woman that there will be days of tiredness or malaise when reducing or adapting the activity is the right thing to do; Davenport and Hayman consider this adjustment part of good guidance (Davenport and Hayman, 2022).

Intensity, athletes and special situations

Most of the evidence comes from studies with walking (Davenport and Hayman, 2022). Much less is known about high-intensity or long-duration activity in pregnancy (Davenport and Hayman, 2022).

Vigorous exercise

The WHO states that women who were already doing vigorous activity before becoming pregnant can continue during pregnancy and the postpartum period (Bull, 2020). The meta-analysis by Beetham and colleagues assessed vigorous exercise in the third trimester in 10 cohorts and 5 trials (Beetham, 2019). It found no difference in birth weight, with a mean difference of 8.06 g across 8,006 pregnancies (Beetham, 2019). The authors conclude that vigorous exercise in the third trimester appears safe for most healthy pregnancies, but they note a lack of data on exertion above 90 out of every 100 beats of maximum heart rate (Beetham, 2019).

Athletes

The scoping review by Wieloch and colleagues gathered 16 studies with pregnant elite and competitive amateur athletes (Wieloch, 2022). No adverse maternal or fetal effects were reported (Wieloch, 2022). Only in intense exercise tests, with the mother above 90 out of every 100 beats of maximum heart rate, did some fetuses show heart rate decelerations (Wieloch, 2022). In one of the reports, a fetal bradycardia of 70 beats per minute after a running sprint recovered to 120 in 3 minutes (Wieloch, 2022).

Davenport and Hayman note that athletes who want to train above the recommendations should do so together with the obstetrician (Davenport and Hayman, 2022). They also point out the other side: reducing the activity of someone who is very active too much can harm physical and mental health through detraining (Davenport and Hayman, 2022). In athletes, the text on relative energy deficiency in sport helps to remember that sufficient energy intake also counts.

When there is no prior activity

Sedentary women before pregnancy should be encouraged to start (Hinman, 2015). The WHO notes that some activity is better than none and that the ideal is to start small and gradually increase frequency, intensity and duration (Bull, 2020). For light or moderate activity, not exceeding the demands of a brisk walk, prior medical clearance is generally unnecessary in those without contraindications (Bull, 2020).

How to advise in practice

With contraindications ruled out and warning signs taught, the guidance still needs to be put together. Hinman and colleagues note that frequency, intensity, type and time should start from the level of activity the woman had before pregnancy (Hinman, 2015).

The elements of the guidance

• Volume: at least 150 minutes per week of moderate aerobic activity, according to the WHO (Bull, 2020).
• Distribution: Davenport and Hayman suggest spreading this volume over at least three days of the week (Davenport and Hayman, 2022).
• Type: combine aerobic activity and muscle strengthening; light stretching may help (Bull, 2020).
• Intensity: the talk test, in which the pregnant woman can hold a conversation during exercise, is a simple guide to moderate intensity (Davenport and Hayman, 2022).
• Pelvic floor: include specific training, which reduces incontinence and severe tears (Zhang, 2024).
• Sedentary behavior: reduce sitting time, since replacing sedentary time with any activity brings benefits (Bull, 2020).

The conversation

The patient who arrives afraid of "dropping the baby" needs more than a list. Motivational interviewing offers tools to explore her beliefs, acknowledge the concern and build the decision together. In the same visit, it is worth recalling other protective measures, such as vaccination during pregnancy.

Back to the case

The pregnant woman at 14 weeks has none of the contraindications in the table. She can return to running at a pace that allows conversation and resume weight training, avoiding lying flat on her back from the second trimester onward. She leaves the visit knowing the warning signs, with pelvic floor training included and guidance to reassess if any complication arises. The family's remark loses force when the answer comes with numbers and a clear plan.

How NEXO helps train this reasoning

In NEXO, the case of the day is fictional, with a real clinical presentation and up to six progressive clues, and you propose the diagnosis by searching for the ICD-10 code.

The limits on using the game are described on the NEXO economy page. If you research the teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information under curation and creators, and institutions can learn about the proposal on the partnerships page. For the most frequent reasons for consultation, see the most common codes in primary care.

Frequently asked questions

Does exercise in pregnancy increase the risk of miscarriage?

Reviews do not show this. Prenatal exercise reduced depression, preeclampsia and gestational diabetes without increasing miscarriage, preterm birth or small for gestational age babies (Davenport and Hayman, 2022).

How much exercise should a pregnant woman do?

The WHO recommends at least 150 weekly minutes of moderate aerobic activity, with muscle strengthening, for pregnant women without contraindications (Bull, 2020).

Who should not exercise during pregnancy?

Pregnant women with gestational hypertension, preeclampsia, rupture of membranes, cervical incompetence, placenta previa, bleeding in the second or third trimester or preterm labor have an absolute contraindication (Hinman, 2015). Even in these cases, bed rest is not recommended (Davenport and Hayman, 2022).

Which signs mean stop exercising?

Vaginal bleeding, dizziness, chest pain, calf pain or swelling, loss of fluid, regular and painful contractions, reduced baby movements and shortness of breath before exertion (Hinman, 2015).

Can those who ran before keep running?

Yes, according to the WHO, which allows continuing vigorous activity in those who already practiced it before pregnancy (Bull, 2020). Vigorous exercise in the third trimester did not change birth weight (Beetham, 2019).

Can athletes train hard during pregnancy?

Yes, with obstetric follow-up. Transient decreases in fetal heart rate only appeared above 90 of every 100 maternal maximum heart rate beats (Wieloch, 2022).

Which activities should be avoided?

Sports with a risk of falling, contact or abdominal trauma, scuba diving and exercise in excessive heat (Davenport and Hayman, 2022).

Take-home messages

• For most pregnant women, exercise is safe and brings benefits for the mother and the baby.
• The goal is at least 150 minutes per week of moderate aerobic activity, with muscle strengthening.
• Before giving guidance, look for absolute and relative contraindications; they are few and objective.
• An absolute contraindication is not a reason for bed rest; everyday activities continue.
• Teach the warning signs for stopping specifically, naming each one and saying where to go.
• Avoid sports with a risk of falling or abdominal trauma, diving and excessive heat.
• Athletes and very active women can keep training, with obstetric follow-up.

Play today's case on NEXO.

References

1. Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020. PMID 33239350. DOI 10.1136/bjsports-2020-102955.
2. Hinman SK, Smith KB, Quillen DM, et al. Exercise in Pregnancy: A Clinical Review. Sports Health. 2015. PMID 26502446. DOI 10.1177/1941738115599358.
3. Davenport MH, Hayman M. Physical activity during pregnancy: Essential steps for maternal and fetal health. Obstet Med. 2022. PMID 36262813. DOI 10.1177/1753495X221122540.
4. Newton ER, May L. Adaptation of Maternal-Fetal Physiology to Exercise in Pregnancy: The Basis of Guidelines for Physical Activity in Pregnancy. Clin Med Insights Womens Health. 2017. PMID 28579865. DOI 10.1177/1179562X17693224.
5. Teede HJ, Bailey C, Moran LJ, et al. Association of Antenatal Diet and Physical Activity-Based Interventions With Gestational Weight Gain and Pregnancy Outcomes: A Systematic Review and Meta-analysis. JAMA Intern Med. 2022. PMID 34928300. DOI 10.1001/jamainternmed.2021.6373.
6. Martínez-Vizcaíno V, Sanabria-Martínez G, Fernández-Rodríguez R, et al. Exercise during pregnancy for preventing gestational diabetes mellitus and hypertensive disorders: An umbrella review of randomised controlled trials and an updated meta-analysis. BJOG. 2023. PMID 36156844. DOI 10.1111/1471-0528.17304.
7. Zhang D, Ruchat SM, Silva-Jose C, et al. Influence of Physical Activity during Pregnancy on Type and Duration of Delivery, and Epidural Use: Systematic Review and Meta-Analysis. J Clin Med. 2023. PMID 37568541. DOI 10.3390/jcm12155139.
8. Zhang D, Bø K, Montejo R, et al. Influence of pelvic floor muscle training alone or as part of a general physical activity program during pregnancy on urinary incontinence, episiotomy and third- or fourth-degree perineal tear: Systematic review and meta-analysis of randomized clinical trials. Acta Obstet Gynecol Scand. 2024. PMID 38140841. DOI 10.1111/aogs.14744.
9. Sánchez-Polán M, Franco E, Silva-José C, et al. Exercise During Pregnancy and Prenatal Depression: A Systematic Review and Meta-Analysis. Front Physiol. 2021. PMID 34262468. DOI 10.3389/fphys.2021.640024.
10. Zhang D, Nagpal TS, Silva-José C, et al. Influence of Physical Activity during Pregnancy on Birth Weight: Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Clin Med. 2023. PMID 37629463. DOI 10.3390/jcm12165421.
11. Wen J, Xun P, Chen C, et al. Non-occupational physical activity during pregnancy and the risk of preterm birth: a meta-analysis of observational and interventional studies. Sci Rep. 2017. PMID 28327589. DOI 10.1038/srep44842.
12. Bauer I, Hartkopf J, Kullmann S, et al. Spotlight on the fetus: how physical activity during pregnancy influences fetal health: a narrative review. BMJ Open Sport Exerc Med. 2020. PMID 32206341. DOI 10.1136/bmjsem-2019-000658.
13. Beetham KS, Giles C, Noetel M, et al. The effects of vigorous intensity exercise in the third trimester of pregnancy: a systematic review and meta-analysis. BMC Pregnancy Childbirth. 2019. PMID 31391016. DOI 10.1186/s12884-019-2441-1.
14. Wieloch N, Klostermann A, Kimmich N, et al. Sport and exercise recommendations for pregnant athletes: a systematic scoping review. BMJ Open Sport Exerc Med. 2022. PMID 36451657. DOI 10.1136/bmjsem-2022-001395.