Patient and public involvement

Participants in previous pilot studies were consulted regarding their satisfaction with the exercise intervention and the characteristics of the exercise professionals.16 These inputs have been used to improve the quality of the interventions. Medical doctors from participating hospitals will collaborate with the research group in recruiting participants, disseminating research findings through publications and seminars and delivering relevant educational content.

Trial design

This is a multicentre, two-arm, parallel-group, randomised controlled trial (RCT) with a 1:1 allocation ratio and an equivalence framework. Pregnant women will be randomly assigned to either an IN or ON supervised multicomponent exercise intervention.

Trial setting

The study will be conducted in healthcare and fitness centres across participating hospitals and universities in Portugal.

Participants

This study aims to include healthy pregnant women (uniparous and multiparous) who, after the first clinical visit and ultrasonically confirmed viable intrauterine pregnancy, will be randomly allocated to one of two groups: exercise intervention delivered IN or ON, after signing an informed consent form.

Eligibility criteria for participants

Inclusion criteria: pregnant women aged 18–50 years; 13–20 weeks of gestation at recruitment; no absolute contraindications to exercise during pregnancy; attending healthcare services regarding pregnancy and understanding the Portuguese language.

Exclusion criteria: medical conditions contraindicating PA and inability to participate in IN or ON formats.

Eligibility criteria for exercise professionals who will deliver the interventions

The exercise intervention will be carried out by graduated exercise professionals (EQF level 6 or 7), holders of a BSc, MSc or PhD in Exercise or Sport Sciences, with specialisation in exercise testing and prescription during pregnancy. Exercise professionals will explain the study’s objectives and obtain informed consent before conducting assessments and delivering the exercise intervention.

Exercise intervention programmes and comparators

The interventions follow international guidelines for PA during pregnancy.7–9 The exercise programme was designed and validated as a complex intervention and underwent three stages: development, pilot testing and evaluation.14 Exercise sessions consist of a combination of aerobic, resistance, stretching, balance, coordination, postural and pelvic floor muscle exercises, using multicomponent activities, such as aerobics, dancing, step, Pilates, bar, chair and resistance exercises using elastic bands, exercise balls, mats, dumbbells or body weight.

Table 1 describes both arms of the exercise intervention in line with the American College of Sports Medicine exercise prescription guidelines.17

Additional materials describing the intervention

Additional recommendations to participants include open-access educational materials, such as the ACTIVE PREGNANCY Guide (online supplemental 1), walking, swimming or performing a video session from the ACTIVE PREGNANCY YouTube Channel on other days of the week.

Exercise physiologists delivering the intervention will be supported by a specific textbook18 and the ACTIVE PREGNANCY YouTube Channel regarding programme planning, exercise testing and prescription and exercise adaptations.

Healthcare professionals providing health screenings and recruiting participants will be supported by the Health Professionals Guide (online supplemental 2).

Individual reports will be provided for each participant and her healthcare provider.

Explanation for the choice of comparators

Despite the existing evidence on prenatal exercise, there is a need for robust, multicentre studies evaluating the impact of both IN and ON exercise interventions on maternal PA, fitness and health outcomes, independent of maternal age, health status or baseline fitness.

Criteria for discontinuing or modifying allocated interventions

Participants will be free to discontinue or modify allocated interventions on request or due to medical reasons without any consequences.

Strategies to improve adherence to interventions

Exercise professionals will monitor adherence to the intervention by recording the number of sessions attended over 12 weeks. Motivational strategies include organising online group meetings, sending weekly WhatsApp and Instagram reminders, providing access to resources promoting an active and healthy lifestyle and offering access to the YouTube channel.

The overall focus of these sessions is based on what already motivates participants to increase or maintain their PA level and healthy lifestyle. This is achieved by fostering interaction among participants to create meaningful group processes, such as support, experience exchange and reflection, as well as collecting feedback regarding the exercise programme and resources. All monthly online sessions will last 20–30 min and are led by exercise and health professionals. These sessions aim: (1) to inform about PA guidelines, benefits associated with PA and possible ways to increase PA during pregnancy; (2) to discuss participant’s barriers, wishes, needs, knowledge and former PA experiences to identify individual characteristics and motivation towards a more physically active lifestyle; (3) to teach the advantages of using a PA tracker, aside from measuring the PA level, the activity trackers are also used as an intervention element to motivate the participants to increase their PA levels, share it on a Strava group and provide feedback on recent PA performances; (4) to collect feedback regarding the organisation of the exercise programme and (5) to discuss other relevant topics chosen by the participants, such as myths about pregnancy PA, postpartum PA, the pelvic floor, uterine contractions, abdominal muscles and diastasis recti, birth, etc.

Individual sessions will be scheduled during the daytime at a time that is as convenient as possible for the participant.

The primary objectives of these motivational strategies are to enhance participant retention and adherence to follow-up, as well as to incorporate a patient-centred approach into the exercise intervention.

Concomitant care permitted or prohibited during the trial

During the exercise trial, participants will be permitted to continue their routine medical care, including medications and consultations with their primary healthcare providers, as well as maintain their usual PA and nutritional habits, such as participation in other organised exercise programmes or specific sports.

Timeline

The schematic diagram of the study, including the schedule of enrolment, data collection points (assessments) at baseline (13–20 gestational weeks) and postintervention (25–32 gestational weeks), interventions and additional collection points, is shown in figures 1 and 2.

Outcomes

Primary, secondary and additional outcome measures, including the specific measurement variables, timeframe and instruments, are shown in table 2.

Harms

Any spontaneously reported adverse events and other unintended effects of trial interventions or health status changes (absolute contraindication for PA) should be immediately reported by the participants, the exercise or the healthcare professionals to the principal researcher.

Sample size

The sample size was determined using G*Power software (V.3.1) based on previous studies. To detect statistical differences between pre- and postdifferences in one group, a sample of 36 pregnant women was considered based on calculations performed using G*Power with the inputs of the mean±SD from previous studies by Dennis et al,19 a power of 0.8 and α≤0.05. Additionally, to detect statistical differences between two independent groups of pregnant women included (experimental) or not (control) in exercise programmes, a sample size of 59 per group was calculated based on the mean±SD values from previous studies by Ramírez-Vélez et al,20 a power of 0.8 and α≤0.05. Based on an expected loss-to-follow-up rate of 20%, we plan to include 100 participants in each of the two intervention groups. Therefore, a total of 200 pregnant women will be recruited and randomly allocated to either the IN or ON group (100 per group).

Recruitment

Recruitment will occur through healthcare centres or hospitals during the first prenatal visit, as well as through social media campaigns and community outreach. Standard care consists of three appointments with their general practitioner or obstetrician (gestational weeks 6–10, 25 and 32), including ultrasonic scans. After the first visit, the woman will be verbally informed about the study by the healthcare professional. An informative flyer and the ACTIVE PREGNANCY Guide (online supplemental 1) will be provided, and written informed consent will be obtained to refer her to an exercise professional participating in the project. The exercise professional will provide further details on the intervention and objectives of the study, and allocation will be concealed to one of the IN or ON groups (figure 1) after checking the inclusion criteria and signing an informed consent. After inclusion, anthropometric and demographic information will be collected, along with a brief interview with the participant. The interview will provide insight into the participant’s thoughts on participating in a research project, as well as their prior and current PA levels, exercise preferences and experiences with health technologies to incorporate a patient-oriented approach into the exercise intervention. Before starting the intervention, the baseline data of the participant are measured.

Assignment of interventions, randomisation and blinding

Blinding will be used by healthcare providers who recruit women and refer them to one of the available programmes. Exercise physiologists will generate a simple random allocation sequence stratified by study sites. Participants, healthcare providers and outcome assessors will not be blinded after assignment to interventions. Data analysts will be blinded after assignment to interventions.

Data collection methods

Data will be collected through online (Google Forms) reliable and validated questionnaires, as well as via IN or ON field test assessments. Training for assessors will be provided to promote data quality. Table 1 includes the description of trial instruments. Data collection forms will be accessed by assessors, principal investigators (PIs) and data analysts. Data will be securely stored and managed following established ethical guidelines. Data from participants who do not complete at least 80% of the scheduled sessions will be considered a loss to follow-up.

Plans to promote participant retention and complete follow-up

Plans to promote retention include the above-mentioned motivational strategies. Moreover, they will be informed about the study’s objectives and dissemination plans. Participants who discontinue or deviate from intervention protocols will be contacted by telephone to provide qualitative feedback and help us understand context-specific issues.

Trial monitoring

The steering group of the research team comprises the PI and senior researchers who participated in planning and will provide organisational support to the trial by involving and supervising students, as well as organising scientific events related to the project. This group will meet every other month. The PI and junior researchers of the team will lead the trial. This group will meet every other week. The PI will be responsible for monitoring trial conduct.

Data management

All data entry will be performed exclusively in electronic format by the exercise professionals. Data coding will be performed using the nine digits of the national VAT number (eg, 123456789). Data quality is checked (eg, missing data, duplicate data entry and range checks for data values) and monitored by the PI and data analysts. Data analysis will be performed by the data monitoring group, which includes PI, assessors and data analysts. Its main role is to check data quality. This group is independent from the sponsor and has no competing interests.

Access to the full protocol, participant-level data and statistical code can be provided by the PI on request and justification.

Data will be analysed according to the intent-to-treat principle and presented following the guidelines of the International Consolidated Test Reporting Standards guidelines 2025.

Statistical methods for primary and secondary outcomes

Demographic data (age, weight, gestational age, area of residence and date of birth) will be described using frequencies and percentages for categorical variables.

Descriptive statistics (mean, SD, median and IQR) will be used to summarise baseline characteristics of participants in both groups (IN and ON).

Descriptive and inferential statistics will be applied to all outcomes.

A comparative analysis of IN versus ON interventions will be conducted using both intention-to-treat and per-protocol approaches. Comparative analysis will be used to compare changes in primary and secondary outcomes between IN and ON groups over time (baseline and postintervention). Subgroup analyses will evaluate potential differences between maternal age groups (<35 vs 35+ years) and PA level groups.

Adherence to the intervention (proportion of attendance in the planned sessions) will be calculated after the postintervention assessments.

Data from participants who do not complete at least 80% of the scheduled sessions will be considered a loss to follow-up.

Regarding additional outcome analysis, the evaluation of interventions and resources will be performed through descriptive analysis, summarising satisfaction with resources and exercise interventions.

Continuous variables will be assessed for normality using Shapiro–Wilk tests. Normally distributed variables will be presented as mean±SD and analysed using the independent sample t-test. The non-normally distributed data will be reported as the median with IQR and will be analysed using the Mann–Whitney test. For the within-group difference, normally distributed variables will be calculated with the paired-sample t-test. In contrast, those non-normally distributed variables will be calculated with the paired-sample non-parametric Wilcoxon test. Categorical data will be analysed using Pearson’s χ² test or Fisher’s exact test, as appropriate.

A significance level of 0.05 (alpha level) will be set for all statistical tests. Power calculations were performed to ensure that the study was adequately powered to detect clinically significant differences between groups. All statistical analyses will be conducted in Statistical Package for the Social Sciences.

Interim analysis

An interim analysis will be performed by the steering group and provided to the research group every 3 months until a final decision is made to terminate the trial.

Post-trial care

After completing 12 weeks of trial participation, including baseline and postintervention assessments, participants will be invited to continue for free until the gestational week of childbirth. They will continue to have access to educational materials after the study ends. Participants will have access to ongoing healthcare and will be invited to participate in a similar trial during the postpartum period.