Effects of prenatal exercise on fetal heart rate, umbilical and uterine blood flow: a systematic review and meta-analysis

Is fetal well-being jeopardised during high-intensity interval training?

ABSTRACT

Objectives

To explore the acute effects of high-intensity interval training on fetal heart rate (FHR) and uteroplacental blood flow.

Method

Elite (n=10) and recreational athletes (n=50) participated in an experimental laboratory study involving 5×5 min intervals of high-intensity exercise on both a treadmill and cycle ergometer, with a 4 min pause between intervals for measurement of FHR and uteroplacental blood flow. Target intensity was 17 on Borg's rating of perceived exertion (RPE) scale and 90% of estimated maximal maternal heart rate (MHRmax).

Results

Mean exercise intensity was 16.4 (SD 1.0) RPE and 89.4 (SD 3.8) % of MHRmax during running and 16.0 (SD 1.0) RPE and 84.6 (SD 5.0) % of MHRmax during cycling. Mean FHR was 140.9 (SD 27.4) beats per minute (bpm) during pauses between running bouts and 148.9 (SD 16.0) bpm during pauses between cycling bouts. Six cases of prolonged fetal bradycardia (<100 bpm for >3 min) occurred during running, leading to the termination of exercise. The mothers exercised at 17-18 on Borg's RPE scale and 86.4%-92.6% of MHRmax in these cases. All cases were normalised within 8 min of ending the protocol. There were no cases of prolonged fetal bradycardia during cycling. Exercise was terminated for three women during running and two women during cycling due to fetal tachycardia (≥180 bpm for >4 min during rest).

Conclusion

Despite cases of fetal bradycardia and tachycardia, our results indicate that highly active women can engage in multiple intervals of high-intensity interval training without apparent harm to fetal well-being.

Consequences of the modulation of gestational resistance training intensity for placental cell composition and nutrient transporter expression

INTRODUCTION

Resistance training during pregnancy provides benefits for the mother and fetus, but little is known about the effects of resistance training on placental structure and function or the repercussions of modifying resistance training intensity on the mother-fetus-placenta triad.

METHODS

Female Wistar rats were submitted to resistance training involving a ladder climb (80 % of maximum load carried (MLC), 5-day/week for 3-weeks) before pregnancy. After confirmation of mating, the rats were randomly divided into three groups, according to resistance training intensity during pregnancy: constant-intensity training (CIT, trained at 80 % of MLC through gestation), decreasing-intensity training (DIT, 80 % of MLC during first and second weeks of gestation and 50 % of MLC in the third week), and undulating-intensity training (UIT, 50 % of MLC in the first and third weeks, and 80 % of MLC in the second week). A control group did not undergo any training. Samples were collected on gestational day 20.

RESULTS

Resistance training had no impact on maternal body weight, muscle glycogen content, adipocyte morphology, number of fetuses, number of absorptions, placental area, or fetal growth parameters. The CIT group presented lower maternal serum glucose. The UIT group presented increased presence of fetal capillaries in the labyrinth zone and increased Glut1, Glut3, and Snat1 expression in the placenta. Snat2 expression was upregulated in all resistance training groups and higher levels of Mtor expression were found in the DIT group. Il1b expression increased in the CIT group, and higher levels of Il10 expression were found in the DIT and UIT groups.

DISCUSSION

Resistance training was safe for pregnant rats. Its influence on glucose and amino acid transport was not dependent on changes in Mtor expression and did not impact fetal growth.

Maternal physical activity in healthy pregnancy: Effect on fetal oxygen supply

AIM

We review evidence for effects of physical activity before and during gestation on the course of pregnancy and ask if there are circumstances where physical activity can stress the fetus due to competition for oxygen and energy substrates.

RESULTS

We first summarize physiological responses to exercise in nonpregnant people and known physiological adaptations to pregnancy. Comparing the two, we conclude that physical activity prior to and continuing during gestation is beneficial to pregnancy outcome. The effect of starting an exercise regimen during pregnancy is less easy to assess as few studies have been undertaken. Results from animal models suggest that the effects of maternal exercise on the fetus are transient; the fetus can readily compensate for a short-term reduction in oxygen supply.

CONCLUSION

In general, we conclude that physical activity before and during pregnancy is beneficial, and exercise started during pregnancy is unlikely to affect fetal development. We caution, however, that there are circumstances where this may not apply. They include the intensive exercise regimens of elite athletes and pregnancies at high altitudes where hypoxia occurs even in the resting state.

Alterations in maternal cardiovascular parameters and their impact on uterine and fetal circulation in hypertensive pregnancies and fetal growth restriction

Objective

To examine potential alterations in maternal cardiovascular parameters in hypertensive pregnancies with or without fetal growth restriction (FGR) in comparison to uncomplicated normotensive pregnancies, and to determine the correlation between maternal cardiovascular parameters and changes in umbilical and uterine artery circulation.

Materials and methods

This study enrolled 73 pregnant women starting from the 20th week of gestation, categorized into three groups: hypertensive conditions (pregnancy-induced hypertension, preeclampsia or eclampsia, n = 30), hypertensive conditions with FGR (n = 8) and a control group of healthy normotensive pregnant women (n = 35). All participants underwent echocardiography to assess cardiac output and calculate peripheral vascular resistance. Additionally, fetal biometric measurements and Doppler ultrasound examinations of the uterine and umbilical artery were performed. The results were standardized into gestational age-adjusted z-scores.

Results

The mean pulsatility index (PI) of the uterine artery (1.36, p < 0.001) and umbilical artery PI z-scores (1.32, p < 0.001) showed significant increases in the hypertensive conditions + FGR group. Maternal cardiac output z-scores were notably lower in both the hypertensive + FGR group (-2.62, p = 0.001) and the hypertensive group (-2.49, p < 0.001). Peripheral vascular resistance was significantly elevated in the hypertensive + FGR group (7.43, p < 0.001) and the hypertensive group (6.06, p < 0.001). There was a positive correlation between maternal peripheral vascular resistance and uterine artery PI (R2 = 0.172; p = 0.0004), and a negative correlation between cardiac output and uterine artery PI (R2 = 0.067; p = 0.031). However, significant correlation between maternal cardiovascular parameters and umbilical artery PI was not identified.

Conclusions

Maternal cardiac output exhibits a significant decrease whereas peripheral vascular resistance increases in hypertensive pregnancies, irrespective of the presence of FGR. Both uterine and umbilical artery PI notably increase when hypertensive pregnancies are accompanied by FGR. A positive correlation exists between maternal peripheral vascular resistance and uterine artery PI, as well as a negative correlation between maternal cardiac output and uterine artery PI. However, changes in maternal cardiovascular parameters do not exhibit significant correlations with umbilical artery PI.

Guidelines for assessing maternal cardiovascular physiology during pregnancy and postpartum

Maternal mortality rates are at an all-time high across the world and are set to increase in subsequent years. Cardiovascular disease is the leading cause of death during pregnancy and postpartum, especially in the United States. Therefore, understanding the physiological changes in the cardiovascular system during normal pregnancy is necessary to understand disease-related pathology. Significant systemic and cardiovascular physiological changes occur during pregnancy that are essential for supporting the maternal-fetal dyad. The physiological impact of pregnancy on the cardiovascular system has been examined in both experimental animal models and in humans. However, there is a continued need in this field of study to provide increased rigor and reproducibility. Therefore, these guidelines aim to provide information regarding best practices and recommendations to accurately and rigorously measure cardiovascular physiology during normal and cardiovascular disease-complicated pregnancies in human and animal models.

Maternal physical activity and sitting time and its association with placental morphology and blood flow during gestation: Findings from the Queensland Family Cohort study

OBJECTIVES

Antenatal exercise is associated with placental morphological alterations, however research in this area is limited. Given the emphasis on the beneficial effects of antenatal exercise, it is important to understand its effect on placental function and the relationship to foetal development. The aim of this study was to investigate the association between physical activity, sitting time, and placental outcomes measured during gestation.

DESIGN

Prospective cohort study.

METHODS

Pregnant women in the Queensland Family Cohort study self-reported physical activity at 24 and 36 weeks of gestation (n = 203) and were categorised into physical activity volume groups of nil-low (0-<500 metabolic equivalent of task·minutes/week), moderate (500-<1000 metabolic equivalent of task·minutes/week), or high-volume activity (≥1000 metabolic equivalent of task·minutes/week). Participants reported average daily sitting time, whereby excessive sitting time was considered as ≥8h/day. Placental stiffness, thickness, and uteroplacental blood flow resistance were measured by ultrasound imaging at each timepoint.

RESULTS

Physical activity volume was not associated with changes to placental morphometrics or uteroplacental blood flow resistance at 24 or 36 weeks of gestation. Excessive sitting time at 36 weeks was associated with greater placental stiffness (p = 0.046), and a lower umbilical artery pulsatility index (p = 0.001).

CONCLUSIONS

Placental tissue stiffness and umbilical artery resistance were altered in late gestation with higher maternal sitting time but not with physical activity volume. Overall, excessive sitting time may be a risk for suboptimal placental function and could be an important focus for antenatal care.

Interval training and cardiometabolic health in reproductive-aged females

Physical activity and exercise training are especially important for reproductive-aged females as exercise-induced health benefits can also affect their infants. However, levels of physical inactivity remain high among females in this age group, before, during, and after pregnancy. There is a great need for practical and feasible exercise modes to increase adherence to exercise in this population, and interval training may be a time-efficient training modality. Interval training is a form of exercise involving intermittent bouts of intense effort interspersed with recovery periods of rest or lower-intensity exercise. A substantial amount of research indicates that interval training induces superior cardiometabolic health benefits compared with iso-energetic moderate-intensity continuous exercise. This review provides a comprehensive overview of research on interval training interventions in reproductive-aged females across various life stages, focusing on the cardiometabolic health benefits. We discuss the potential role of interval training in premenopausal females with overweight/obesity, polycystic ovary syndrome, and subfertility, as well as the potential influence of oral contraceptives on cardiometabolic adaptations to interval training. Furthermore, this review also highlights recent findings supporting the beneficial role of high-intensity interval training for cardiometabolic health outcomes during pregnancy. In summary, the existing evidence suggests that interval training can improve several cardiometabolic and reproductive outcomes in females spanning different life stages. However, more research is needed to further strengthen the evidence-base for physical activity recommendations for females in their reproductive years of life.

A narrative review of exercise dose during pregnancy

The current recommendations for prenatal exercise dose align with those from the American College of Sports Medicine; 150 min of moderate intensity every week of pregnancy. However, recent works suggest there may be a dose-dependent beneficial effect for mother and offspring; maternal and offspring health outcomes respond differently to low, medium, and high doses of prenatal exercise. It is, therefore, our aim to summarize the published evidence (years 1950-2023) for five metrics of prenatal exercise training commonly reported, that is, "FITT-V": Frequency (number of sessions), Intensity (metabolic equivalents "METs"), Time (duration of sessions), Type (exercise mode), Volume (exercise MET*mins). The target audience includes clinicians and health care professionals, as well as exercise professionals and physiologists. Data suggest that moderate exercise frequency (3-4 times weekly) appears safe and efficacious for mother and offspring, while there is contradictory evidence for the safety and further benefit of increased frequency beyond 5 sessions per week. Moderate (3-6 METs) and vigorous (>6 METs) intensity prenatal exercise have been shown to promote maternal and offspring health, while little research has been performed on low-intensity (<3 METs) exercise. Exercise sessions lasting less than 1 hr are safe for mother and fetus, while longer-duration exercise should be carefully considered and monitored. Taken together, aerobic, resistance, or a combination of exercise types is well tolerated at medium-to-high volumes and offers a variety of type-specific benefits. Still, research is needed to define (1) the "minimum" effective dose of exercise for mother and offspring health, as well as (2) the maximum tolerable dose from which more benefits may be seen. Additionally, there is a lack of randomized controlled trials addressing exercise doses during the three trimesters of pregnancy. Further, the protocols adopted in research studies should be more standardized and tested for efficacy in different populations of gravid women.

Maternal and Fetal Cardiovascular Responses to Acute High-Intensity Interval and Moderate-Intensity Continuous Training Exercise During Pregnancy: A Randomized Crossover Trial

OBJECTIVE

We aimed to compare maternal and fetal cardiovascular responses to an acute bout of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) during pregnancy.

METHODS

Fifteen women with a singleton pregnancy (27.3 ± 3.5 weeks of gestation, 33 ± 4 years of age) were recruited. Following a peak fitness test, participants engaged in a session of HIIT (10 × 1-min intervals ≥ 90% maximum heart rate [HRmax]) interspersed with 1 min of active recovery) and MICT (30 min at 64-76% HRmax) 48 h apart in random order. Maternal HR, blood pressure, middle (MCAv), and posterior cerebral artery blood velocity (PCAv), as well as respiratory measures were monitored continuously throughout HIIT/MICT. Fetal heart rate, as well as umbilical systolic/diastolic (S/D) ratio, resistive index (RI), and pulsatility index (PI) were assessed immediately before and after exercise.

RESULTS

Average maternal heart rate was higher for HIIT (82 ± 5% HRmax) compared with MICT (74 ± 4% HRmax; p < 0.001). During the HIIT session, participants achieved a peak heart rate of 96 ± 5% HRmax (range of 87-105% HRmax). Maternal cerebral blood velocities increased with exercise but was not different between HIIT and MICT for MCAv (p = 0.340) and PCAv (p = 0.142). Fetal heart rate increased during exercise (p = 0.244) but was not different between sessions (HIIT: Δ + 14 ± 7 bpm; MICT: Δ + 10 ± 10 bpm). Metrics of umbilical blood flow decreased with exercise and were not different between exercise sessions (PI: p = 0.707; S/D ratio: p = 0.671; RI: p = 0.792). Fetal bradycardia was not observed, and S/D ratio, RI, and PI remained within normal ranges both before and immediately after all exercise sessions.

CONCLUSIONS

An acute bout of HIIT exercise consisting of repeated 1-min near-maximal to maximal exertions, as well as MICT exercise is well tolerated by both mother and fetus.

CLINICAL TRIAL REGISTRATION

NCT05369247.

Applying Scientific Rationale to the Current Perceptions and Explanations of Massage and Miscarriage in the First Trimester

Miscarriage is a relatively common occurrence, impacting 8-15% of clinically recognised pregnancies, and up to 30% of all conceptions. The public perception of the risk factors associated with miscarriage does not match the evidence. Evidence indicates that there are very few modifiable factors to prevent miscarriage, and the majority of the time little could have been done to prevent a spontaneous miscarriage. However, the public perception is that consuming drugs, lifting a heavy object, previous use of an intrauterine device, or massage can all contribute to miscarriage. While misinformation about the causes and risk factors of miscarriage continues to circulate, pregnant women will experience confusion about what activities they can (and cannot) do in early pregnancy, including receiving a massage. Pregnancy massage is an important component of massage therapy education. The resources that underpin pregnancy massage coursework consist of educational print content that includes direction and caution that massage in the first trimester, if done 'incorrectly' or in the 'wrong' location, can contribute to adverse outcomes such as miscarriage. The most common statements, perceptions and explanations for massage and miscarriage cover three broad areas: 1) maternal changes from massage affects the embryo/fetus; 2) massage leads to damage of the fetus/placenta; and 3) aspects of the massage treatment in the first trimester initiate contractions. The goal of this paper is to use scientific rationale to critically consider the validity of the current perceptions and explanations of massage therapy and miscarriage. Whilst direct evidence from clinical trials was lacking, considerations of physiological mechanisms regulating pregnancy and known risk factors associated with miscarriage provide no evidence that massage in pregnancy would increase a patient's risk of miscarriage. This scientific rationale should be addressed when teaching pregnancy massage courses.

Recent Patterns of Physical Activity and Sedentary Behaviour Among Pregnant Adults in Canada

OBJECTIVE

To evaluate current levels of physical activity and sedentary behaviour among pregnant and non-pregnant adults in Canada.

METHODS

We ascertained population-based cross-sectional data from the Canadian Community Health Survey (CCHS), 2015-2019, and the Canadian Health Measures Survey (CHMS), 2007-2019. We included adults who were assigned female at birth and were of reproductive age (aged 18-55 years) living in the provinces. We analyzed activity data from validated questionnaires and accelerometers.

RESULTS

We included 53 765 adults from the CCHS and 5321 from the CHMS, weighted to represent 16 million people. Based on accelerometers, both pregnant and non-pregnant adults spent 9.5 hours per day (70% of their time) engaged in sedentary behaviour. Across all survey years, ages, and Canadian regions, pregnant adults, especially those aged under 35 years, spent less time engaged in moderate-to-vigorous physical activity (MVPA) compared with non-pregnant adults. Pregnant adults reported 34.3 minutes (95% CI 30.5-38.2) and objectively accrued 14.9 minutes (95% CI 7.9-21.8) in MVPA per day - 15.1 and 8.9 fewer minutes than non-pregnant adults, respectively. After accounting for self-report bias, only 27.5% (95% CI 24.1-31.0) of the pregnant and 41.1% (95% CI 40.4-41.9) of the non-pregnant adults met the Canadian physical activity guidelines (i.e., ≥150 minutes of MVPA per week).

CONCLUSION

Physical activity levels are remarkably low among both pregnant and non-pregnant adults, with few meeting current guidelines. Given the substantial physical and mental health benefits, more support is needed to increase pre-pregnancy and prenatal activity in Canada.

Beneficial Effects of Maternal Physical Activity during Pregnancy on Fetal, Newborn, and Child Health: Guidelines for Interventions during the Perinatal Period from the French National College of Midwives

The objective of this work is to synthesize current knowledge about the effects of maternal physical activity during pregnancy on children's health. During the prenatal and postnatal periods, maternal physical activity has protective effects against the risks of macrosomia, obesity, and other associated cardiometabolic disorders. Even though longitudinal studies in humans are still necessary to validate them, these effects have been consistently observed in animal studies. A remarkable effect of maternal physical activity is its positive role on neurogenesis, language development, memory, and other cognitive functions related to learning.

Sports Obstetrics: Implications of Pregnancy in Elite Sportswomen, a Narrative Review

Increasing numbers of females are participating in elite sports, with a record number having competed at the Tokyo Olympic Games. Importantly, the ages of peak performance and fertility are very likely to coincide; as such, it is inevitable that pregnancy will occur during training and competition. Whilst there is considerable evidence to promote regular exercise in pregnancy, with benefits including a reduction in hypertensive disorders, gestational diabetes, and reduced rates of post-natal depression, few studies have been conducted which include elite athletes. Indeed, there are concerns that high-intensity exercise may lead to increased rates of miscarriage and preterm labour, amongst other pregnancy-related complications. There is minimal guidance on the obstetric management of athletes, and consequently, healthcare professionals frequently adopt a very conservative approach to managing such people. This narrative review summarises the evidence on the antenatal, intrapartum, and postpartum outcomes in elite athletes and provides recommendations for healthcare providers, demonstrating that generally, pregnant athletes can continue their training, with a few notable exceptions. It also summarises the physiological changes that occur in pregnancy and reviews the literature base regarding how these changes may impact performance, with benefits arising from pregnancy-associated cardiovascular adaptations at earlier gestations but later changes causing an increased risk of injury and fatigue.

Development of the Get Active Questionnaire for Pregnancy: Breaking down barriers to prenatal exercise

Evidence-based guidelines represent the highest level of scientific evidence to identify best-practices for clinical/public health. However, the availability of guidelines do not guarantee their use, targeted knowledge translation strategies and tools are necessary to help promote uptake. Following publication of the 2019 Canadian Guideline for Physical Activity throughout Pregnancy, the Get Active Questionnaire for Pregnancy, and an associated Health Care Provider Consultation Form for Prenatal Physical Activity were developed to promote guideline adoption and use amongst pregnant individuals and health care providers. This paper describes the process of developing these tools. First, a survey was administered to qualified exercise professionals to identify the barriers and facilitators in using existing prenatal exercise screening tools. A Working Group of researchers and stakeholders then convened to develop an evidence-informed exercise pre-participation screening tool for pregnant individuals, building from previous tool and survey findings. Finally, end-user feedback was solicited through a survey and key informant interviews to ensure tools are feasible and acceptable to use in practice. The uptake and use of these documents by pregnant individuals, exercise and health care professionals will be assessed in future studies. Novelty Bullets • Evidence supports the safety/benefits of exercise for most pregnant individuals; however, exercise is not recommended for a small number of individuals with specific medical conditions. • The Get Active Questionnaire for Pregnancy and Health Care Provider Consultation Form for Physical Activity during Pregnancy identify individuals where prenatal exercise may pose a risk, while reducing barriers to physical activity participation for the majority of pregnant individuals.

Acute fetal response to high-intensity interval training in the second and third trimesters of pregnancy

The majority of women do not meet the recommended levels of exercise during their pregnancies, frequently due to a lack of time. High-intensity interval training offers a potential solution, providing an effective, time-efficient exercise modality. This exercise modality has not been studied in pregnancy therefore, the objective of this study was to evaluate fetal response to a high-intensity interval training resistance circuit in the late second and early third trimesters of pregnancy. Fourteen active, healthy women with uncomplicated, singleton pregnancies participated in a high-intensity interval training resistance circuit between 28 + 0/7 and 32 + 0/7 weeks. A Borg rating of perceived exertion of 15-17/20 and an estimated heart rate of 80%-90% of maternal heart-rate maximum was targeted. Fetal well-being was evaluated continuously with fetal heart-rate tracings and umbilical artery Doppler velocimetry conducted pre-and post-exercise. Fetal heart rate tracings were normal throughout the exercise circuit. Post-exercise, umbilical artery end-diastolic flow was normal and significant decreases were observed in the mean systolic/diastolic ratios, pulsatility indexes and resistance indexes. Therefore, in a small cohort of active pregnant women, a high-intensity interval training resistance circuit in the late second and early third trimesters of pregnancy appears to be a safe exercise modality with no acute, adverse fetal effects but further study is required. Novelty: High-intensity interval training, at an intensity in excess of current recommendations, does not appear to be associated with any adverse fetal effects in previously active pregnant women. High-intensity interval training is an enjoyable and effective exercise modality in previously active pregnant women.

Cardiac Responses to Submaximal Isometric Contraction and Aerobic Exercise in Healthy Pregnancy

PURPOSE

The increased physiological demand of pregnancy results in the profound adaptation of the maternal cardiovascular system, reflected by greater resting cardiac output and left ventricular (LV) deformation. Whether the increased resting demand alters acute cardiac responses to exercise in healthy pregnant women is not well understood.

METHODS

Healthy nonpregnant (n = 18), pregnant (n = 14, 22-26 wk gestation), and postpartum women (n = 13, 12-16 wk postdelivery) underwent assessments of cardiac function and LV mechanics at rest, during a sustained isometric forearm contraction (30% maximum), and during low-intensity (LOW) and moderate-intensity (MOD) dynamic cycling exercise (25% and 50% peak power output). Significant differences (α = 0.05) were determined using ANCOVA and general linear model (resting value included as covariate).

RESULTS

When accounting for higher resting cardiac output in pregnant women, pregnant women had greater cardiac output during isometric contraction (2.0 ± 0.3 L·min-1·m-1.83; nonpregnant, 1.3 ± 0.2 L·min-1·m-1.83; postpartum, 1.5 ± 0.5 L·min-1·m-1.83; P = 0.02) but similar values during dynamic cycling exercise (pregnant, LOW = 2.8 ± 0.4 L·min-1·m-1.83, MOD = 3.4 ± 0.7 L·min-1·m-1.83; nonpregnant, LOW = 2.4 ± 0.3 L·min-1·m-1.83, MOD = 3.0 ± 0.3 L·min-1·m-1.83; postpartum, LOW = 2.3 ± 0.4 L·min-1·m-1.83, MOD = 3.0 ± 0.5 L·min-1·m-1.83; P = 0.96). Basal circumferential strain was higher in pregnant women at rest, during the sustained isometric forearm contraction (-23.5% ± 1.2%; nonpregnant, -14.6% ± 1.4%; P = 0.001), and during dynamic cycling exercise (LOW = -27.0% ± 4.9%, MOD = -27.4% ± 4.6%; nonpregnant, LOW = -15.8% ± 4.5%, MOD = -15.2% ± 6.7%; P = 0.012); however, other parameters of LV mechanics were not different between groups.

CONCLUSION

The results support that the maternal heart can appropriately respond to additional cardiac demand and altered loading experienced during acute isometric and dynamic exercise, although subtle differences in responses to these challenges were observed. In addition, the LV mechanics that underpin global cardiac function are greater in pregnant women during exercise, leading to the speculation that the hormonal milieu of pregnancy influences regional deformation.

Elite Athletes and Pregnancy Outcomes: A Systematic Review and Meta-analysis

PURPOSE

The purpose of this systematic review was to evaluate fetal and maternal pregnancy outcomes of elite athletes who had participated in competitive sport immediately before conception.

METHODS

Online databases were searched up to March 24, 2020. Studies of any design and language were eligible if they contained information on the relevant population (pregnant women), exposure (engaged in elite sport immediately before pregnancy), and outcomes (birth weight, low birth weight, macrosomia, preterm birth, fetal heart rate and pulse index, cesarean sections, instrumental deliveries, episiotomies, duration of labor, perineal tears, pregnancy-induced low back pain, pelvic girdle pain, urinary incontinence, miscarriages, prenatal weight gain, inadequate/excess prenatal weight gain, maternal depression or anxiety).

RESULTS

Eleven unique studies (n = 2256 women) were included. We identified "low" certainty evidence demonstrating lower rates of low back pain in elite athletes compared with active/sedentary controls (n = 248; odds ratio, 0.38; 95% confidence interval, 0.20-0.73; I2 = 0%) and "very low" certainty evidence indicating an increased odds of excessive prenatal weight gain in elite athletes versus active/sedentary controls (n = 1763; odds ratio, 2.47; 95% confidence interval, 1.26-4.85; I2 = 0%). Low certainty evidence from two studies (n = 7) indicated three episodes of fetal bradycardia after high-intensity exercise that resolved within 10 min of cessation of activity. No studies reported inadequate gestational weight gain or maternal depression or anxiety. There were no differences between elite athletes and controls for all other outcomes.

CONCLUSIONS

There is "low" certainty of evidence that elite athletes have reduced odds of experiencing pregnancy-related low back pain and "very low"certainty of evidence that elite athletes have increased the odds of excessive weight gain compared with active/sedentary controls. More research is needed to provide strong evidence of how elite competitive sport before pregnancy affects maternal and fetal outcomes.PROSPERO Registration: CRD42020167382.

Prenatal Exercise and Cardiorespiratory Health and Fitness: A Meta-analysis

PURPOSE

This study aimed to examine the influence of prenatal exercise on maternal cardiorespiratory health and fitness during pregnancy.

METHODS

Online databases were searched up to February 25, 2019. Studies of randomized controlled trials (RCTs) were eligible, which contained information on the relevant population (pregnant women), intervention (subjective or objective measures of frequency, intensity, duration, volume, or type of exercise), comparator (no exercise intervention), and outcomes (maternal cardiorespiratory fitness, including V˙O2max, submaximal V˙O2, V˙O2 at anaerobic threshold, and cardiorespiratory health, including resting heart rate, and resting systolic and diastolic blood pressures during pregnancy).

RESULTS

From 2699 unique citations, 26 RCTs (N = 2292 women) were included. Of these, one study reported measured V˙O2max, seven reported predicted V˙O2max, three reported submaximal V˙O2, and two studies reported VO2AT. "Low"- to "high"-certainty evidence revealed that exercise was associated with improved predicted/measured V˙O2max (5 RCTs, n = 430; mean difference [MD], 2.77 mL·kg·min; 95% confidence interval [CI], 0.32 to 5.21 mL·kg·min; I = 69%), reduced resting heart rate (9 RCTs, n = 637; MD, -1.71 bpm; 95% CI, -3.24 to -0.19 bpm; I = 13%), resting systolic blood pressure (16 RCTs, n = 1672; MD, -2.11 mm Hg; 95% CI, -3.71 to -0.51 mm Hg; I = 69%), and diastolic blood pressure (15 RCTs, n = 1624; MD, -1.77 mm Hg; 95% CI, -2.90 to -0.64 mm Hg; I = 60%).

CONCLUSION

Prenatal exercise interventions improve maternal predicted/measured V˙O2max and reduce resting heart rate and blood pressure. This review highlights the need for additional high-quality studies of cardiorespiratory fitness (namely, V˙O2max and V˙O2 peak) in pregnancy.PROSPERO registration number: CRD42019131249.

Cardiopulmonary exercise testing during pregnancy

The goal of this review is to examine practical considerations when conducting cardiopulmonary exercise testing during pregnancy. In a clinical and research setting, cardiopulmonary exercise testing during pregnancy is valuable in identifying underlying cardiopulmonary conditions, stratifying the risk of adverse pregnancy outcomes, as well as establishing exercise tolerance/limitations. This review encompasses information regarding the unique physiological adaptations that occur throughout gestation (e.g., changes in resting heart rate, blood pressure, glucose, etc.) and how these adaptations impact the interpretation of physiological measurements. There are also key concerns that are unique to pregnant populations that should be considered when participating in exercise (i.e., fetus, ventilation, thermoregulation, urinary incontinence, low back pain, and pelvic girdle pain). This step-by-step review of cardiopulmonary exercise testing outlines pregnancy related adjustments to standardized methods (i.e., screening/documentation, pre- and post-test measurements, protocol specifics, modality selection, and fetal monitoring) which should be considered for the safety of both the participant and fetus. Currently, pregnancy specific exercise testing guidelines are lacking. Therefore, we will be discussing the limitations of current recommendations such as a safe cut off for resting heart rate and pregnancy specific test termination criteria.

Maternal Lifestyle Interventions: Targeting Preconception Health

About one-third of women of reproductive age are obese, predisposing both mother and baby to unfavourable pregnancy outcomes and initiating an intergenerational cycle of chronic metabolic disorders. Here we summarise recent research on the influence of maternal metabolic health on offspring susceptibility to future cardiometabolic diseases. Current primary lifestyle approaches (i.e., diet and exercise interventions) to halt the succession of inherited and epigenetic metabolic abnormalities have met with limited success due to late implementation, poor adherence, and/or generic guidelines. In our opinion, such interventions must commence prior to conception to improve both maternal and child health outcomes, with new approaches urgently needed to increase adherence to primary lifestyle changes among reproductive-age women.

Why can't I exercise during pregnancy? Time to revisit medical 'absolute' and 'relative' contraindications: systematic review of evidence of harm and a call to action

BACKGROUND

Clinical guidelines recommend pregnant women without contraindication engage in regular physical activity. This is based on extensive evidence demonstrating the safety and benefits of prenatal exercise. However, certain medical conditions or contraindications warrant a reduction, modification or cessation of activity due to potential health risks.

AIM

To review and evaluate the evidence related to medical disorders which may warrant contraindication to prenatal exercise.

METHODS

Online databases were searched up to 5 April 2019. Forty-four unique studies that reported data on our Population (pregnant women with contraindication to exercise), Intervention (subjective/objective measures of acute or chronic exercise), Comparator (not essential) and Outcomes (adverse maternal or fetal outcomes) were included in the review.

KEY FINDINGS

We found that the majority of medical conditions listed as contraindications were based on expert opinion; there is minimal empirical evidence to demonstrate harm of exercise and benefit of activity restriction. We identified 11 complications (eg, gestational hypertension, twin pregnancy) previously classified as contraindications where women may in fact benefit from regular prenatal physical activity with or without modifications. However, the evidence suggests that severe cardiorespiratory disease, placental abruption, vasa previa, uncontrolled type 1 diabetes, intrauterine growth restriction, active preterm labour, severe pre-eclampsia and cervical insufficiency are associated with strong potential for maternal/fetal harm and warrant classification as absolute contraindications.

CONCLUSION

Based on empirical evidence, we provide a call to re-evaluate clinical guidelines related to medical disorders that have previously been considered contraindications to prenatal exercise. Removing barriers to physical activity during pregnancy for women with certain medical conditions may in fact be beneficial for maternal-fetal health outcomes.

Spotlight on the fetus: how physical activity during pregnancy influences fetal health: a narrative review

Before and during pregnancy, women often aim to improve their lifestyle so as to provide a healthier environment for their developing child. It remains unresolved, however, as to whether physical activity (PA) during pregnancy poses a possible risk or whether it might even have beneficial effects on the developing child. There is increasing evidence that PA during pregnancy is indeed beneficial to maternal physiological and psychological health and that it is generally not detrimental to the fetal cardiovascular system and neuronal function in the developing child. This also led to international recommendations for PAs during pregnancy. In the current review, we aimed to comprehensively assess the evidence of beneficial and harmful effects of maternal PA, including high-performance sports, on fetal development. The different mental and body-based relaxation techniques presented here are frequently performed during pregnancy. We found a considerable number of studies addressing these issues. In general, neither low key, moderate maternal PA nor relaxation techniques were observed to have a harmful effect on the developing child. However, we identified some forms of PA which could have at least a transient unfavourable effect. Notably, the literature currently available does not provide enough evidence to enable us to make a general conclusive statement on this subject. This is due to the lack of longitudinal studies on the metabolic and cognitive effects of regular PA during pregnancy and the wide diversity of methods used. In particular, the kind of PA investigated in each study differed from study to study.

Influence of maternal aerobic exercise during pregnancy on fetal cardiac function and outflow

BACKGROUND

Risk factors for cardiovascular disease, the leading cause of death, have been documented in children as young as 3 years of age. Maternal environment (eg, exercise) influences fetal development and long-term health. Thus, the development of the fetal cardiovascular system during pregnancy is likely a preliminary indicator of cardiac health at birth and a proxy for the future risk of cardiovascular disease throughout life.

OBJECTIVE

The purpose of this study was to assess the effects of supervised prenatal aerobic exercise at recommended levels on fetal cardiac function and outflow in the third trimester of pregnancy. We hypothesized that fetuses of aerobically trained women compared with fetuses of nonexercising women would exhibit increased cardiac function and greater cardiac output.

STUDY DESIGN

Secondary data analyses of a 20-week, randomized controlled exercise intervention trial in pregnant women between 2015 and 2018 in Eastern North Carolina were performed. Eligibility criteria included pregnant women <16 weeks gestation, singleton pregnancy, aged 18-40 years, body mass index of 18.5-34.99 kg/m², physician clearance letter for exercise participation, reliable transportation, and method of communication. Exclusion criteria included the presence of chronic conditions (eg, type 1 or 2 diabetes mellitus), current medications known to adversely affect fetal growth (eg, antidepressants), alcohol, smoking, or illicit drug use. The patient cohort consisted of 133 eligible pregnant women who were assigned randomly to either an aerobic exercise (n=66) group that participated in 150 minutes of supervised, moderate-intensity (40-59% VO_2peak; 12-14 on Borg Rating of Perceived Exertion) aerobic exercise per week or a nonexercising group (n=61) that consisted of 150 minutes per week of light (<40% VO_2peak) stretching and relaxation breathing techniques. Between 34 and 36 weeks gestation, a fetal echocardiogram was performed to assess fetal cardiac function, which included fetal heart rate, right- and left-ventricular stroke volume, stroke volume index, cardiac output, cardiac output index, and cardiac outflow that included pulmonary and aortic valve diameters, peak flow velocity, and peak flow velocity-time integral. Fetal activity state (quiet vs active) during the echocardiogram and maternal aerobic capacity served as covariates. Intention-to-treat and per-protocol (participants who attended ≥80% of exercise sessions) analysis of covariance regression models were performed.

RESULTS

Of the 127 randomly assigned participants, 66 and 50 participants were included in the intention-to-treat and per-protocol analyses, respectively. Prenatal aerobic exercise significantly increased fetal right-ventricular cardiac measures of right ventricular stroke volume (P=.001) and stroke index via velocity-time integral (P=.003), right ventricular cardiac output (P=.002), cardiac index via velocity-time integral (P=.006), pulmonary artery diameter (P=.02), and pulmonary valve velocity-time integral (P=.03). Only in the intention-to-treat analysis was a significant difference in fetal left ventricular cardiac outflow observed; there was a greater aortic valve peak velocity (P=.04) found among fetuses of aerobically trained pregnant women. No other statistically significant between-group differences were found.

CONCLUSION

The findings of this study demonstrate that participation in prenatal aerobic exercise at recommended levels may improve fetal cardiac function and outflow parameters. Follow-up cardiovascular measures in the postnatal period are needed to determine potential long-term effects on the offspring's cardiac function and outflow.

Review of Recent Physical Activity Guidelines During Pregnancy to Facilitate Advice by Health Care Providers

Importance

Physical activity during pregnancy can offer many maternal and fetal health benefits.

Objective

The aim was to summarize American, Canadian, and international recommendations published recently on physical activity during pregnancy to aid health care providers in their delivery of advice on the topic.

Evidence Acquisition

A descriptive review of 3 national guidelines and 1 international guideline on physical activity during pregnancy was conducted. The guidelines included the 2019 Canadian recommendations, the 2018 United States' Physical Activity Guidelines for Americans (second edition), the 2015 (reaffirmed in 2017) American College of Obstetrics and Gynecology guideline, and the 2016-2018 International Olympic Committee recommendations for recreational and elite athletes.

Results

For apparently healthy women, under the guidance of their health care provider, moderate-intensity physical activity using both aerobic and muscle conditioning activities is recommended. The guidelines recommended at least 150 min/wk spread throughout the week (Canada, United States) or at least 20 to 30 min/d (American College of Obstetrics and Gynecology).

Conclusions and Relevance

This summary of 4 recent guidelines can facilitate use of updated recommendations by health care providers regarding physical activity during pregnancy. More detailed evidence-based guidelines on physical activity during postpartum are needed.

2019 Canadian guideline for physical activity throughout pregnancy

The objective is to provide guidance for pregnant women and obstetric care and exercise professionals on prenatal physical activity. The outcomes evaluated were maternal, fetal or neonatal morbidity, or fetal mortality during and following pregnancy. Literature was retrieved through searches of MEDLINE, EMBASE, PsycINFO, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Scopus and Web of Science Core Collection, CINAHL Plus with Full Text, Child Development & Adolescent Studies, Education Resources Information Center, SPORTDiscus, ClinicalTrials.gov and the Trip Database from inception up to 6 January 2017. Primary studies of any design were eligible, except case studies. Results were limited to English-language, Spanish-language or French-language materials. Articles related to maternal physical activity during pregnancy reporting on maternal, fetal or neonatal morbidity, or fetal mortality were eligible for inclusion. The quality of evidence was rated using the Grading of Recommendations Assessment, Development and Evaluation methodology. The Guidelines Consensus Panel solicited feedback from end users (obstetric care providers, exercise professionals, researchers, policy organisations, and pregnant and postpartum women). The development of these guidelines followed the Appraisal of Guidelines for Research and Evaluation II instrument. The benefits of prenatal physical activity are moderate and no harms were identified; therefore, the difference between desirable and undesirable consequences (net benefit) is expected to be moderate. The majority of stakeholders and end users indicated that following these recommendations would be feasible, acceptable and equitable. Following these recommendations is likely to require minimal resources from both individual and health systems perspectives.

Impact of prenatal exercise on neonatal and childhood outcomes: a systematic review and meta-analysis

Objective

We aimed to identify the relationship between maternal prenatal exercise and birth complications, and neonatal and childhood morphometric, metabolic and developmental outcomes.

Design

Systematic review with random-effects meta-analysis and meta-regression.

Data sources

Online databases were searched up to 6 January 2017.

Study eligibility criteria

Studies of all designs were eligible (except case studies and reviews) if published in English, Spanish or French, and contained information on the relevant population (pregnant women without contraindication to exercise), intervention (subjective/objective measures of frequency, intensity, duration, volume or type of exercise, alone (‘exercise-only’) or in combination with other intervention components (eg, dietary; ‘exercise+cointervention’)), comparator (no exercise or different frequency, intensity, duration, volume, type or trimester of exercise) and outcomes (preterm birth, gestational age at delivery, birth weight, low birth weight (<2500 g), high birth weight (>4000 g), small for gestational age, large for gestational age, intrauterine growth restriction, neonatal hypoglycaemia, metabolic acidosis (cord blood pH, base excess), hyperbilirubinaemia, Apgar scores, neonatal intensive care unit admittance, shoulder dystocia, brachial plexus injury, neonatal body composition (per cent body fat, body weight, body mass index (BMI), ponderal index), childhood obesity (per cent body fat, body weight, BMI) and developmental milestones (including cognitive, psychosocial, motor skills)).

Results

A total of 135 studies (n=166 094) were included. There was ‘high’ quality evidence from exercise-only randomised controlled trials (RCTs) showing a 39% reduction in the odds of having a baby >4000 g (macrosomia: 15 RCTs, n=3670; OR 0.61, 95% CI 0.41 to 0.92) in women who exercised compared with women who did not exercise, without affecting the odds of growth-restricted, preterm or low birth weight babies. Prenatal exercise was not associated with the other neonatal or infant outcomes that were examined.

Conclusions

Prenatal exercise is safe and beneficial for the fetus. Maternal exercise was associated with reduced odds of macrosomia (abnormally large babies) and was not associated with neonatal complications or adverse childhood outcomes.