Background

Physical activity (PA) is defined as “bodily movement produced by skeletal muscles that results in energy expenditure” [1]. PA is believed to be essential to healthy pregnancy. Historically, Biblical writers noticed that Hebrew slave women gave birth more easily than sedentary Egyptian mistresses [2]. Moreover, it is believed that PA during pregnancy limits gestational weight-gain [3,4,5], decreases risk of maternal mental disorders after childbirth [6, 7] and improves body image satisfaction [8]. PA in pregnancy is pivotal to facilitating positive health outcomes in infants [9].

To corroborate the role of PA in pregnancy and the expected favourable health outcomes for pregnant women and infants, this study distinguishes between the terms PA, exercise (intervention), and physical fitness that are all distinct concepts. However, these concepts (terms) are often used interchangeably. In line with a seminal paper, we deem exercise as “a subset of PA that is planned, structured, and repetitive and has as a final or an intermediate objective the improvement or maintenance of physical fitness”. In addition, physical fitness is deemed “a set of attributes that are either health- or skill-related” [10].

Pregnant women tend to demonstrate a lack of knowledge regarding PA during pregnancy [9, 11, 12]. The reasons for insufficient knowledge include but are not limited to the mothers’ race [13], socio-economic and cultural context [14], and maternal education [15]. Relatively low degree of pregnant women report that they had received prescription in terms of exercise interventions from health providers during pregnancy [16]. In addition, past research identified an important barrier to enhancing pregnant women’ knowledge about PA—the absence of PA-related domains in the development of professional healthcare professionals [17]. Due to lack of guidance, pregnant women access information about healthy lifestyle during pregnancy via the internet with questionable credibility [18, 19].

Mottola et al. who performed a literature review and identified some benefits of prenatal PA, provided preliminary guidance for pregnant women and healthcare professionals on prenatal PAity [20]. Unsurprisingly, the women who were given guidelines for PA during pregnancy reported exercising [21].

In addition to potential issues with credible sources of information and lack of novel guidance, healthcare professionals need multiple sources to develop an “integrative approach” for promotion of PA to pregnant women [22, 23]. From the standpoint of the authors,an “integrative approach” should, for instance, account for tailored exercise interventions that could be useful to pregnant women with specific goald, and facilitate the adherence of pregnant women to PA [24, 25].

The aim of the current study is hence two-fold. First, we respond to more-recent calls for evidence-based recommendations that would enhance promotion of PA during pregnancy (see e.g., [26]). We have listed and contextualized the recommendations to be provided to pregnant women, professional healthcare professionals involved in nursing (e.g., midwives), and wider society. Further, by identifying exercise modalities, examining characteristics of exercise interventions with a systematic review, and corresponding health outcomes we address a recent call from DiPietro et al. [27] to advance current knowledge and empower healthcare professionals. As interventions should be tailored (e.g., goal-oriented to a physical-fitness components), our second aim is to characterize the interventions from main findings, and further elaborate characteristics such as exercise modality. By corroborating the exercise interventions for pregnant women, we can enhance the adherence to PA and improve the promotion of PA among the healthcare professionals. Ultimately, the current study concludes with the contributions to the learning system and an identification of intricate contemporary challenges to be addressed in the future research.

Methods

Design

A systematic review is a summary of the medical literature that uses explicit and reproducible methods to systematically search, critically appraise, and synthesize a specific health issue [28]. Following steps were taken into account when performing a systematic review: (1) defining research question; (2) preliminary literature search; (3) development of search string, inclusion and exclusion criteria; (4) literature search and analysis; (5) literature synthesis; (6) assessment of literature quality and bias; and (7) interpretation of findings and proposition of future directions. When performing a systematic review, the Additional file 1: PRISMA guidelines were followed [25] (Additional file 1: Appendix 1).

Search methods

For the development of research question, a Population, Intervention and Outcome—PICO [29] format was used. The research question was: How do exercise interventions improve the health of physically-active pregnant women and their infants? Exclusion and inclusion criteria were developed based on the preliminary literature search and PICO research question (Table 1).

Table 1 Search criteria and inclusion and exclusion criteria
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We searched for literature published between June 2017 and June 2022, in English language and RCTs. As described by Hiebl [30], authors can limit their literature search by publication time. However, reasons should be justified and mentioned in the limitation section. The aim of this systematic review is to get the newest and best evidence in this field, thus, only literature published in last five years were examined. We provide up-to-date evidence which is often neglected by authors of overviews [31]. We included only RCTs because they are assessed as the most credible in the hierarchy of evidence [23]. Other studies were excluded (Additional file 1).

A search string was developed based on preliminary literature search and was taken into account in the process of literature search (Table 2).

Table 2 Search results
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Search outcomes

Using the developed search string 2092 records were identified in four databases. After duplicates exclusion, literature was checked by title and abstract; 26 articles were retrieved and checked by the full text. Finally, 20 articles were included in the final analysis and synthesis. Steps of literature search are presented in Fig. 1 [32].

Fig. 1
figure 1

PRISMA flow diagram

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Quality appraisal

The data quality was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system [33, 34]. GRADE identified its five categories—study limitations, imprecision, inconsistency, indirectness, and publication bias. GRADE quality level is interpreted as high (++++), moderate (+++), low (++), or very low (+).

Data extraction

Data were extracted using standardized data form in Microsoft Excel® by two reviewers. The first reviewer exported data and second reviewer checked for data accuracy. The literature screening was carried out independently by two researchers. Disagreements were solved by consensus. We extracted study characteristics such as study sample, exercise intervention, main study results and conclusions.

Data synthesis

A narrative synthesis was conducted for all included studies. Results were synthesized by PA modality and intensity or duration of PA. Also, results were synthesised due to the intervention effectiveness.

Results

In total, 20 articles were included in the final analysis (Table 3). Studies which fit the inclusion criteria were analysed due to sample, intervention, results and conclusions. Excluded studies are listed in the Additional file 2: Appendix 2.

Table 3 Study characteristics
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Studies included in the analyses involved various number of participants. Those numbers varied between minimum of 20 [27] and maximum of 1023 pregnant women [38]. All studies had intervention and control group. However, all studies did not report mean and standard deviation for each group. Interventions were the following: moderate aerobic exercise, lumbar stabilization and stretching exercise, resistance training, water exercise, various moderate-intensity exercises, physical conditioning program, cycling program, nerve and tendon-slip exercise, and individual or group sessions with a personal trainer. Studies outcomes are assessed as positive or negative for pregnant women or infant in the Table 4. Details about each intervention are provided in the Table 5. In the remainder of this study the observed studies are assessed for quality using the GRADE system (table in Additional file 3: Appendix 3). All studies included were RCTs because of the search criteria. RCTs are seen as a high-quality body-of-knowledge [34]. When assessing quality of each evidence, study design, study limitations, inconsistency, indirectness, imprecision and risk of bias were considered. The results of the assessment are as follows. Among 18 units-of-analysis, three were assessed as moderate quality, eight as low quality, and seven as very low quality. In these seven, quality scored was lower due to numerous limitations (e.g., the absence of the control group, small study sample, lack of blinding, lack of robust analyses, etc.), higher deviations in CIs for interventions, or risk of bias.

Table 4 Data synthesis by intervention and results
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Table 5 An in-merge of evidence-based exercise interventions by the exercise modality
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Out of 20 identified RCTs, 11 (55.00%) reported positive results of implemented intervention on maternal or infant health outcomes (Table 4). Others showed no changes or did not report the result.

To help professional healthcare professionals in promoting PA we further categorize interventions by exercise modality (Table 5). Among a range of exercise modalities, four exercise modalities, namely strengthening, stretching, balance, and aerobic exercises, are commonly found in the existing body of literature that focuses on positive results of physical activity interventions on health outcomes [52,53,54,55].

Table 5 categorizes main findings with respect to exercise modality and their expected positive results on pregnant-women health and well-being. The favourable health outcomes of performing moderate aerobic exercise were most extensively examined [35, 45], followed by strengthening see e.g., [42], or a hybrid form using both [38, 44]. For aerobic exercise, treadmill, walking, and other aerobic-exercise programs are advised (see Table 5). A more comprehensive hybrid form of PA program included moderate aerobic exercise with gradual warm-up; aerobics; light muscle strengthening; balance; stretching; strengthening; and relaxation with final talk [35]. In addition, [56] proposed an exercise program of both aerobic and strength training among Norwegian pregnant women to examine vitamin-D mediated effect on maternal and fetal health outcomes.

Some of the remaining studies also focused on specific sub-types of, for instance, stretching [36], and aerobic exercise [47]. In fact, practitioners are advised to suggest pregnant women the tendon slip exercises and the nerve-gliding exercises. Gestational diabetes mellitus was the main research subject by [4]. Authors revealed that, complementary to healthy eating, exercise limits the gestational weight gain. What is more, their findings pinpoint to a comprehensive approach, comprised of, for instance, moderate PA, reducing sedentary time, and strengthening.

Fontana Carvalho et al. [36] reported that involved pregnant women were included in either lumbal stabilization exercise group or lower limb and trunk stretching exercise group. Both interventions showed positive results in pain reduction caused by or perceived as a result of pregnancy. Rodríguez-Blanque et al. [38] reported that pregnant women performed a moderate PA consisting of a warm-up; aerobic exercise, strengthening, and stretching with relaxation to limit the negative effects on the body and to optimise well-being, mood and sleep patterns. Finally, positive results were also seen by combing individual diet and PA [39]. Moreover, PA intervention entailed positive results in maternal diet quality. Similarly, [40] proposed a supervised PA program consisting of warm-up, aerobic exercise, strengthening, balance, and stretching with relaxation. Hereby, intensity of PA was mild-to-moderate. The PA showed positive results in weight loss at 6 weeks post-partum.

Among the combined exercise modalities, [35] introduced a 10-min warm-up (walking and stretching) with a main section that lasted 30–35 min and included moderate intensity aerobic and resistance exercises. Activity ended with a cool down (walking, stretching, relaxation and pelvic floor muscle training). Gustafsson et al. [45] proposed a 12-week standardized PA program where women were encouraged to perform exercise modalities at home at least twice a week. Fontana Carvalho et al. [36] reported success of exercise interventions with a combination of stabilization of lower limbs and stretching. With an aim of reducing carpal-tunnel symptoms, pregnant women also conducted tailored nerve and tendon slip exercises on daily basis [41]. With respect to duration, [44] suggested water exercise to be followed for 12 weeks. Finally, a PA program aimed at conditioning was developed to encourage pregnant women to perform exercises throughout the entire pregnancy [40].

Discussion

Our findings reveal that past research on PA in pregnancy focused mostly on health outcomes for the pregnant women and infants. Similar to Evenson et al. (2014), our analysis revealed heterogeneity of findings in terms of exercise modality, duration, and intensity. To overcome some of these shortcomings, we call for a standardization in terms of measurable and comparative characteristics of PA in pregnancy. Following this train-of-thought, a commonly used FITT framework (see e.g., [57]) has been applied to numerous sub-domains where exercise prescriptions from the healthcare professionals play a significant role, ranging from patients with cancer [58], exercise prescriptions for cardiometabolic health [59], and occasionally as a one-size-fits-all to general population [60].

Applying a framework similar to FITT to pregnant women would allow for quantifying the common characteristics of PA in pregnancy (e.g., intensity). The development of such framework that would guide the hands-on recommendations from the healthcare professionals would require acknowledging for any challenges pregnant women might have as a result of, for instance, deteriorating health, lack of physical fit, and maturity of pregnancy [61, 62]. Finally, a growing number of pregnant women have a propensity to remain physically fit notwithstanding pregnancy. Physical fitness is defined as a»state characterized by: (a) an ability to perform daily activities with vigour; and (b) demonstration of traits and capacities that are associated with low risk of premature development of physical inactivity [63]. In a broader sense, one’s physical fitness represents their capability to carry out a range of exercise modalities and daily tasks. Campbell et al. [64] emphasize the need to improve this capability concomitantly with the management any fatigue, stress, or change in health condition which is especially relevant assertion to the pregnant women. Moreover, there is a need for development of efficient physical activity interventions for pregnant women. Marini et al. [65] proposed a study protocol to design physical activity intervention for pregnant women to include in childbirth preparation classes evaluating its feasibility and efficacy on quality of life, PA levels and other outcomes.

The physical fitness is achieved, maintained and facilitated by prescribing exercise that accounts for the components of physical fitness. These components might differ with respect to the existing literature; however, most commonly the components are cardiorespiratory fitness [66], muscular strength [67], muscular endurance [68], body composition [69], and flexibility [55, 70]. Elaborating on the physical-fitness components could reveal complementary outcomes (in addition to health outcomes identified by the current study and past research) relevant to pregnant women that aim to advance their PA. We suggest the future research to focus on further examination of the complementary role of maintaining physical fitness, to account for the associated health- and physical-fitness-related outcomes, and to overcome aforementioned context-based challenges for pregnant women (e.g., timing of PA).

The existing learning system in nursing can advance by moving towards an integrative approach that accounts for multiple sources, network collaboration, and continuous investigation of PA. We facilitate the learning processes of healthcare professionals by elaborating on exercise modalities, and commencing a discussion over the components of physical fitness. Acknowledging physical-fitness components could enhance adherence of pregnant women to PA (see e.g., [39]), and empower healthcare professionals who promote PA.

It is evident that research does not focus on different components of PA or components of physical fitness. In line with DiPietro et al. [27] we argue that the future research should focus on providing recommendations tailored for the »peri-pregnancy« period, i.e. before, during, and after a childbirth. Second; whilst the current study adds to tailoring exercise interventions by elaborating exercise modality and physical-fitness components, lack of detailed information not only about pregnant women but also about the pre-pregnancy condition prevents from optimizing interventions for particular cohorts of pregnant women.

Future research should focus on multiple sources to overcome aforementioned challenges that limit the development of tailored evidence-based PA recommendations. Furthermore, we suggest that, in addition to health outcomes, the future research devotes more attention to the role and plausibility of PA for achieving or maintaining physical-fitness components of pregnant women. Such enriched guidelines could enhance adherence and favourable health outcomes of pregnant women, and improve promotion of PA among the healthcare professionals. However, future research should identify appropriate healthcare professionals to distribute PA recommendations (see e.g., [23]), and, in addition, barriers that prevent from effective distribution of physical activity recommendations. Finally, to complement the existing body of the literature with PA recommendations for pregnant women, future research should ensure the scientific nature of such reviews by e.g., addressing the listed limitations, and expanding the data obtained.

The current study reveals a lack of context-dependency, for instance characteristics of pregnant women such as age, previous PA levels, comorbidities, other measures (e.g., BMI), mental well-being, pregnancy status (e.g., early or late pregnancy, health issues during pregnancy, micronutrient levels etc.), non-communicable diseases with viral infections (see e.g., [71, 72]), and other factors such as personal attitude (see e.g., [73]) that could compromise the development and realization of PA. However, the current study also has some methodological limitations in addition to the limited feasibility of data analysis. First, we deliberately examined the more-recent literature in order to get novel and credible selection of evidence. We omitted analysing non-published papers or papers without a free access. Second, a heterogeneity of findings partially prevented from more thorough analyses. Finally, we did not use data processing software, which to some degree reduces the reliability of the qualitative analysis.

Conclusion with research agenda

The current study demonstrates numerous favourable health outcomes of PA during pregnancy. Recommendations given by practitioners to pregnant women focus on preforming at least 150 min per week moderate-intensity aerobic PA. However, further explanations are not provided. That being said, practitioners can use our systematic literature review to examine favourable maternal and infant health outcomes with a range of exercise modalities (strengthening, balance, stretching, and exercise modalities combined) in addition to aerobic exercise. Furthermore, the practitioners can learn from the current study about the importance of physical-fitness components. As adherence is consistently deemed a critical success factor for PA [74], accounting for the physical-fitness components, i.e., goal-oriented (tailored), in exercise interventions, could remarkably improve the adherence of pregnant women to PA.