The benefits of exercise during pregnancy on maternal, fetal, and newborn well-being are well known (13,29,33). In fact, not leading a healthy lifestyle during pregnancy challenges the normal process of pregnancy and childbirth leading to poor nutritional habits, sedentary lifestyle, and physical and mental stress (20,34,35,37). An unhealthy lifestyle increases the risk for complications to maternal (hypertension, gestational diabetes [GDM], and prenatal depression) and fetal health (macrosomia, intrauterine growth restriction, etc.). Some studies report a positive association of pathologies for children later in life (overweight, obesity, type 2 diabetes, cardiovascular disease, and mental and emotional problems) (5,11,18,21). Excessive weight gain during pregnancy and large or small birth weight babies are the most relevant parameters linked to these complications, and consequences result in a significant public health problem (9,12,36).
Most scientific studies have focused on examining the influence of different intervention factors on pregnancy outcome as a possible solution. Many studies have presented positive results for maternal and fetal outcomes using physical exercise during pregnancy as an independent variable (8,30). However, very few studies have compared modality of exercise (land versus aquatic) and examined the differences, if any, between these two modalities with regard to pregnancy outcome. Although we and others have reported positive health benefits for maternal and fetal outcomes as a result of land-based exercise (20,34,37), some authors maintain the idea of the aquatic environment as the best choice for movement during pregnancy (23,24,39). These opinions are based on positive effects generated by the thermal dissipation and physical support of the water environment that may improve blood circulation and venous return, mobility, and present a positive body image (39).
Promoting exercise during pregnancy is not an easy task as women are concerned about safety. Currently, no randomized controlled trial (RCT) exists comparing these two most common forms of exercise during pregnancy with equivalent workloads between modalities regarding weight gain and pregnancy outcomes. Thus, it is necessary to investigate if the benefits of each modality separately are reflected in the combination of land-based and water-based activities. By examining pregnancy outcomes of each modality compared with the combination, we may provide pregnant women with a choice of which type of modality they prefer with clinically based evidence for safety.
The aim of the present study was to compare the cross-sectional results from three experimental studies conducted on land (study 1 ), in water (study 2 ), and in mixed form (land + water; study 3 ) using the same designs and equivalent workloads on maternal weight gain, gestational diabetes mellitus development, pregnancy-induced hypertension, gestational age, birth weight, and Apgar scores in healthy pregnant women from different Spanish-speaking areas. Although each RCT was published separately, we provide a unique opportunity to compare the data generated as a cross-sectional investigation. It was hypothesized that the mixed group of land + water (study 3) would have the best pregnancy outcomes, compared with land (study 1) or water (study 2) exercise groups. We predict that the combined program may be best because this may present positive outcomes from both modalities of exercise.
Three RCT results were compared cross-sectionally to determine which modality of exercise was best at controlling excessive gestational weight gain, gestational diabetes mellitus, pregnancy-induced hypertension, and birth weight.
- i) Study 1: land (three sessions per week), NCT01696201 (7)
- ii) Study 2: aquatic activities (three sessions per week), NCT02602106 (3)
- iii) Study 3: land (two sessions per week) + aquatic activities (one session per week), NCT01790412 (15)
The general characteristics of each of the studies were the same: several healthy Spanish-speaking pregnant women were invited to participate at the first prenatal visit. All women randomized into the control group (CG) for each of the three studies were pooled into one CG that received standard care. Women randomly assigned to the exercise group (EG) in all three studies participated in a program that consisted of three 55- to 60-min sessions per week that began between 9 and 11 wk of gestation and continued until the end of the third trimester (weeks 39–40).
Study 1 (land-based exercise only)
The exercise intensity for the land sessions was set through maternal heart rate, assessed by a heart rate monitor (Accurex Plus; Polar Electro OY, Kempele, Finland), and intensity did not surpass 55%–60% of the calculated heart rate reserve [(220 − age) − (resting heart rate) × 60%] + resting heart rate (19). In addition, Borg's scale between 6 (without effort) and 20 (maximum effort) was used (34) and maintained at the level of 12–14; that is, somewhat hard (33). To maximize patient safety and adherence to the training program and its efficacy, all of the sessions were supervised by a qualified fitness specialist (working with groups of 10–12 participants) with the assistance of an obstetrician. Specific information on exercise methodology is published elsewhere (7).
Study 2 (aquatic exercise only)
In the aquatic sessions, the exercise program was performed in swimming pools of different depths, depending on the type of exercise. The exercise intensity was set through Borg's scale and maintained at the levels of 12 to 14; that is, somewhat hard (33), similar to study 1 (land-based activity). The structure was the same in all of the aquatic sessions, and the women started in the shallow area of the swimming pool, with a gradual warm-up that consisted of 8–10 min of walking at different intensities, static stretching of most muscle groups, and joint mobility exercises. The central part of the work was divided between the following:
- a) aerobic exercises or dance (accompanied by music) 8–10 min in the shallow pool
- b) strength exercises and aquatic activities (propulsion exercises) in standing, supine, and ventral position for 8–10 min in the shallow pool
- c) freestyle swimming (except butterfly style) for 8–10 min
Finally, 10–12 min at the end of each session was spent on the cooldown that included static stretching, relaxing, breathing, and flotation exercises in the shallow pool.
Aquatic materials like foam-rubber balls of different sizes and swimming accessories such as floats, pull-boys (buoyancy aiding devices), water noodles, armbands, and rubber rings were used. Swimming mitts and floating weights for resistance were provided for muscle conditioning. Water temperature was recorded at 28.5°C–29°C.
Study 3: combination exercise study (land + aquatic)
Study 3 (land + aquatic activities) was based on a combination of studies 1 and 2 with the weekly program structure as two sessions on land and one session of aquatic activities. The exercise intensities for the combined land- and water-based sessions were similar to the previous two studies. More information on the aquatic exercise session is found in Cordero et al. (15).
Pregnant women living in Madrid, Spain (studies 1 and 3), and Buenos Aires, Argentina (study 2), who underwent ultrasound examination at 9 to 11 wk of pregnancy were invited to participate. Written informed consent was obtained from each participant. The studies were approved by the Research Ethics Committee of Hospital Universitario de Puerta de Hierro (Madrid, Spain), Hospital Universitario de Fuenlabrada (Madrid, Spain), and Universidad de Flores (Buenos Aires, Argentina), and each study was conducted according to the ethical guidelines of the Declaration of Helsinki, which was last modified in 2008.
Women presenting any type of absolute obstetrical contraindication to exercise as suggested by the American College of Obstetricians and Gynecologists (1) were excluded. Other exclusion criteria were as follows: not planning to give birth in the obstetrics department of the study hospitals, not receiving medical follow-up throughout the pregnancy, participating in another physical activity program, or having a high level of pregestational physical exercise (four or more times per week). Because participating in another structured exercise program was an exclusion criterion, this was verified in the EG at the beginning of the study. Women in the CG confirmed (via telephone interview) that they did not participate in a structured exercise program throughout their pregnancies (5).
Participants for each study were allocated by a computer-generated list of random numbers. Three different authors were responsible for carrying out the randomization process, which consisted of a sequence generation, allocation concealment, and implementation. Women who did not meet the minimum of 80% of adherence to each exercise program were excluded from analysis.
Demographic and other information (pregravid weight and height), parity, occupational activity, previous physical activity habits, smoking status, previous preterm birth, previous low birth weight, and previous miscarriage were obtained at the first prenatal visit (between 9 and 11 wk gestation). Prepregnancy body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared, and women were classified as underweight (BMI < 18.5), normal weight (BMI ≥ 18.5–24.9), overweight (BMI ≥ 25–29.9), and obese (BMI ≥ 30) (22).
Data corresponding to total maternal weight gain (kg), gestational age (d), birth weight (g), and Apgar scores were obtained from medical records from each study. Gestational weight gain was calculated from body weight at the last clinic visit before delivery (within 1–2 wk) minus prepregnancy weight obtained at the first prenatal visit. Recommended maternal weight gain according to prepregnancy BMI was used following the Institute of Medicine (IOM) recommendations of underweight, normal weight, overweight, and obese women, which are 12.5 to 18 kg, 11.5 to 16 kg, 7 to 11.5 kg, and 5 to 9 kg, respectively (22).
Data related to pregnancy outcome were also obtained from medical records at delivery for each study. Preterm delivery was determined as <37 wk of gestation (38). Newborns were classified as having macrosomia when birth weight was >4000 g, and low birth weight was defined as <2500 g (40).
Descriptive statistics included mean and SD for normally distributed continuous variables and frequency and percentage for categorical variables. To examine differences in pregnancy outcomes between study groups, we analyzed and compared data from four groups: intervention groups from studies 1, 2, and 3 and the CG pooled together (given the characteristics of pregnant women in the CG of all studies were identical). Continuous data (age, yr; maternal weight gain, kg; birth weight, g; gestational age, d) were analyzed using a one-way ANOVA. Nominal data (n/%) (BMI categories, parity, smoking, previous physical activity, miscarriage, preterm birth and low birth weight, excessive maternal weight gain, preterm delivery, birth weight categories, gestational diabetes mellitus, hypertension, and Apgar scores) were compared between study groups using χ2 test for descriptive characteristics and pregnancy outcomes. The level of significance was set at P = 0.05.
Cohen's d and contingency coefficient were used to determinate the effect size. An effect size ranging from 0 to 0.20 was considered a small effect size, 0.20 to 0.50 was a moderate effect size, and more than 0.50 was a large effect size (14). The results are presented as the mean ± SD.
Initially, 998 pregnant women were contacted at their first prenatal visit in the three studies. All of the patients had an uncomplicated and singleton gestation. The following numbers of participants were analyzed in each study: study 1, EG = 107 and CG = 93; study 2, EG = 49 and CG = 62; and study 3, EG = 101 and CG = 156. We analyzed a total of 568 participants (31.8 ± 4 yr) for the present study.
Of the total number of women initially contacted, 265 women were excluded: declined to participate (n = 96), not meeting inclusion criteria (n = 144), and other reasons (n = 25). A total of 733 pregnant women were allocated in studies 1, 2, and 3 (see Fig. 1).
The follow-up process of each study participant was as follows:
- a) Study 1 (7): In the EG, 30 pregnant women were lost to follow-up for the following reasons: discontinued intervention (n = 12), risk for premature delivery (n = 1), pregnancy-induced hypertension (n = 1), and personal and other reasons (n = 16), leaving 107 women for analyzes. In the CG, 21 women were lost to follow-up for the following reasons: discontinued participation (n = 7), treatment for premature delivery (n = 3), pregnancy-induced hypertension (n = 2), and personal reasons (n = 9), leaving 93 women for analyzes.
- b) Study 2 (3): In the EG, 21 women were lost to follow-up for the following reasons: discontinued intervention (n = 7), risk for premature delivery (n = 5), diagnosed incompetent cervix (n = 4), and personal reasons (n = 5). In the CG, 8 women were lost to follow-up because of pregnancy-induced hypertension (n = 1), risk for premature delivery (n = 2), and personal reasons (n = 5). This left 49 women for analyses in the EG and 62 women in the CG.
- c) Study 3 (15): In the EG, 21 pregnant women were lost to follow-up for the following reasons: discontinued intervention (n = 7), risk for premature delivery (n = 3), hypertension (n = 2), diagnosed incompetent cervix (n = 2), and personal and other reasons (n = 7), leaving 101 women who were analyzed. In the CG, 64 pregnant women were lost to follow-up for the following reasons: restricted intrauterine growth (n = 3), risk for premature delivery (n = 3), hypertension (n = 2), premature rupture of membranes (n = 2), and personal and other reasons (n = 54).
Therefore, 568 pregnant women were analyzed. For each of the studies, the number of women in the EG group totaled 107 for study 1, 49 women for study 2, and 101 women for study 3. A total of 311 women represented the CG (pooled together from all three studies).
Maternal characteristics: Background variables of the study populations are shown in Table 1. There were no significant differences (P > 0.05) in background variables between study groups.
Maternal and newborn outcomes: Table 2 provides an overview of the main variables of this cross-sectional study. Results for total maternal weight gain (kg) showed that only study 1 had statistical differences with the CG (11.7 vs 13.4 kg, P = 0.001, Cohen's d = 0.38), and similar results were found in the percentage of pregnant women with excessive gestational weight gain (20.6%, n = 22, vs 37.9%, n = 118; P = 0.005, χ2 = 16.6, OR = 0.42, 95% confidence interval = 0.25–0.71).
Birth weight in study 1 (3186.6 ± 500 g) was less than that in study 2 (3376 ± 348 g, P = 0.01) and study 3 (3324 ± 427 g, P = 0.02) and not different from the pooled CG. When baby weight was stratified into birth weight categories, there was no difference between any of the groups.
No statistical differences were found in gestational age and Apgar scores between any of the groups of study (Table 2).
Statistical differences were found for the number of pregnant women with gestational diabetes between the CG (n = 22/7.1%) and studies 2 (0/0%) and 3 (n = 1/1%), P = 0.03, χ2 = 8.9. No differences were found in the percentage of women with hypertension between groups of study. The remaining pregnancy outcomes analyzed present no statistical differences between groups (Table 2).
The aim of the present study was to compare the cross-sectional results of maternal and fetal outcomes from three experimental studies performed in healthy pregnant women. The most important novelty of the current study is comparing three different exercise-based interventions in a pregnant population with the same baseline characteristics. There were no adverse effects of different types of physical exercise on maternal and newborn well-being. Land exercise (study 1) may be preferred to control excessive maternal weight gain over aquatic exercise (study 2) and the combination of land + aquatic (study 3) exercise because land exercise (study 1) was the only modality that showed a reduction compared with women who did not exercise. By contrast, aquatic (study 2) exercise and the combination of land + aquatic (study 3) exercise may be preferred to reduce the incidence of GDM over land (study 1) exercise alone, as these two modalities (aquatic and land + aquatic) were different than the control women with no exercise. The reduction in excessive gestational weight gain with land exercise (study 1) may be related to the smaller birth weight also seen in study 1 compared with aquatic exercise (study 2) or the combination of land and water exercise (study 3). Stratifying by birth weight categories eliminated this difference between exercise modalities. Further study is needed to confirm these results.
Furthermore, we found a lower maternal weight gain in study 1 compared with the CG (P = 0.001) showing a moderate effect size (0.38), which may indicate that land-based exercise may be a clinically preferred choice for exercise prescription to prevent excessive gestational weight gain. Other authors report similar RCT results after examining the influence of aerobic or resistance exercise programs (performed on land) during pregnancy on maternal weight gain (6,31,37) and GDM (2,16,17,41). In contrast to our study, others found that aerobic exercise (land) also decreased the incidence of hypertension (27).
Studies examining aquatic activities during pregnancy showed no influence of the water intervention on pregnancy outcomes (4,10,24,28). Apparently, the best benefits of exercise in water are related to postural and perceptual factors such as physical comfort, improvement in mobility, and postural balance (23,25,26). Analysis of activity patterns of pregnant women has shown that walking is the most popular followed by aquatic aerobic exercise (32).
Nascimento et al. (32) retrospectively assessed the physical activity levels of 1279 pregnant women within 72 h postdelivery. The authors observed that walking was the most popular activity, followed by aquatic aerobics. Promoting physical activity remains a priority in public health policy, and women of childbearing age, especially those planning a pregnancy, should be encouraged to adopt an exercise routine or maintain an active lifestyle during pregnancy to avoid sedentary- and obesity-associated risks.
Granath et al. (19) compared the effect of a land-based program versus water aerobics on low back or pelvic pain and sick leave during pregnancy in 390 healthy pregnant women. The intervention was performed once a week and the authors measured sick leave, pregnancy-related low back pain or pregnancy-related pelvic girdle pain, or both and found that water aerobics reduced pregnancy-related low back pain and sick leave. The authors did not report results on maternal and fetal pregnancy outcomes.
Our results and other studies show relevant differences between land and water exercise programs. These differences may be explained because aquatic exercise has several perceived advantages over land-based exercise according to pregnant women. Immersion in water decreases gravitational pull and pregnant women suggest that buoyancy creates a feeling of physical comfort, improves posture, and improves mobility (23). Comparatively speaking, land exercise may generate the perception of a harder workload for pregnant women compared with water exercise where the buoyancy of the water relieves gravitational pull. In addition, aquatic exercise alone may promote more strength and conditioning activity rather than aerobic weight-bearing activity seen in land-based exercise. Perhaps these differences in gravitational pull when aerobic and resistance exercises are performed on land compared with immersed in water may explain why our land-based exercise program controlled maternal weight gain better than water exercise. Future study should determine the mechanisms involved in different modalities of exercise on maternal weight gain.
Limitations and strengths
The main limitation of our study was the difference between the sample size of each of the intervention groups, creating difficulty in analysis and comparison. Other limitations were that our study examined programs performed in two different geographical areas (Madrid and Buenos Aires), although protocols and mechanisms used in the two regions for clinical trials were identical. Many cultural and social factors that influenced the results may potentially exist and were impossible to control. Nutritional information was not collected from each region of study, which may have influenced our results; however, each woman was receiving similar care from their health care providers. We did not compare education or socioeconomic status between studies at baseline, which also may have influenced our results.
An important strength was examining the influence of two more common forms or structures of supervised exercise programs (separately and combined) on pregnant women and the resultant fetal outcomes. Because these programs appear safe for mother and baby, it may be beneficial to offer pregnant women a choice of either land based, aquatic, or a combination of these two most popular activities to promote a healthy lifestyle.
In summary, our results show that exercise performed on land is more effective than aquatic activities in preventing excessive maternal weight gain, whereas combined programs (land + aquatic) or water exercise programs seem to be more effective in preventing gestational diabetes and that both modes of exercise or a combination is safe for mother and baby. Although more RCT are needed to confirm these results, health care providers may use specific modalities for exercise prescription to provide appropriate healthy pregnancy outcomes.
This study was partially supported by the Technical University of Madrid, Spain; Flores University, Argentina (AL16-PID-15); and the Spanish Ministry of Culture, Education and Sport (PRX15/00249).
The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation, and the results of the present study do not constitute endorsement by the American College of Sports Medicine.
The authors declare no conflict of interest.
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