The searches identified 6155 potentially eligible publications, reducing to 3144 after duplicates were removed. Following title and abstract screening, 263 reports were screened as potentially eligible, and of these, six were inaccessible due to no author response, and 18 met the review eligibility criteria (Fig. 1). In these 18 studies, 1934 pregnant women were randomised to either a comparator (48.4%) or intervention (51.6%) group, with an overall retention rate of 76.5% with 754 and 725 women analysed in the intervention and comparator group, respectively.
Characteristics of included trials
Most studies were conducted in the United States (n = 10) [17, 18, 20,21,22, 26, 27, 29,30,31] and Australia (n = 4) [15, 23,24,25] with the remainder in the UK (n = 2) [19, 28] and Canada (n = 2) [14, 16]. Trials recruited pregnant women with various body mass index (BMI) inclusion criteria. Studies restricted recruitment to women with a BMI ≥18.5 [17, 18, 29], or ≥ 19 [19], or ≥ 20 [25], or ≥ 25.0 [21, 22, 24, 26, 31], ≥30.0 [15, 16, 28], or ≤ 40.0 [14] with four trials not including a BMI restriction [20, 23, 27, 30]. For trials measuring gestational weight gain, seven [14,15,16, 21, 24, 25, 27] calculated this through directly measured weight by researchers; however, four [17, 22, 26, 29] calculated this based on participant measured pre-pregnancy weight and one did not specify the basis of the calculation [23]. Of the 18 included studies, those reporting ethnicity, education and marital status determined that 59% of the participants were White [16, 18, 20,21,22,23, 25, 28, 30, 31], with 75.1% graduating from higher education [14, 16, 18,19,20,21,22, 24, 25, 30, 31] and 88.9% living with partners [14, 16, 18,19,20,21, 28, 31].
Thirteen of the included interventions were categorised as multi-component lifestyle sessions that included physical activity [14, 15, 17, 19,20,21,22, 24, 25, 28,29,30,31]; however, five were exclusively physical activity interventions [16, 18, 23, 26, 27] aimed at promoting physical activity through a timetabled regime. Furthermore, intervention durations were primarily until birth [14, 15, 17, 19, 21, 22, 26, 27, 29,30,31] but 8- [28], 12- [16, 18, 20, 25] and 14-week [23, 24] interventions were also included. Furthermore, 66.7% of follow-up measurements took place at 34-38 weeks gestational age [14,15,16,17, 19, 25,26,27,28,29,30,31] with the remainder varying from intervention end [18, 23, 24] and other timepoints [20,21,22]; however, no last follow-up measurements were taken later than gestational week 38. Fourteen trials used accelerometers [14, 16,17,18,19, 21,22,23, 25, 26, 28,29,30,31] and four used pedometers [15, 20, 24, 27] to measure physical activity as a trial outcome. See Table S4 for details regarding the specific devices used.
Synthesis of results
Total physical activity at last follow-up
Seventeen trials measured the outcome of total physical activity [14, 16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31] via steps per day (n = 11) [14, 16,17,18, 20, 23,24,25,26,27, 30], minutes of light, moderate and vigorous physical activity per week (n = 2) [19, 28], vector magnitude (VM) counts per minute (n = 2) [22, 31], activity expenditure via kcal (n = 1) [21] and MET minutes per week (n = 1) [29]. No significant differences were found between the intervention and comparator group at last follow-up for total physical activity (95% confidence interval [CI] -0.03 to 0.27, p = 0.10, I
2 40%) with a Cohen’s d effect of 0.12 [36]. See Fig. 2. Multi-component lifestyle interventions had a larger effect on total physical activity than exclusively physical activity-based interventions with Cohen’s d effect sizes of 0.16 (95% CI -0.02 to 0.34, p = 0.09, I
2 37%) and 0.06 (95% CI -0.24 to 0.35, p = 0.71, I
2 57%) respectively. See Fig. S1.
Total Physical activity at 24 to 30 weeks gestation (mid pregnancy)
Ten studies [14, 16,17,18, 24, 26,27,28,29, 31] measured total physical activity with data from 24 to 30 weeks gestation (see Fig. S2). No significant differences were found between the intervention and comparator group at this time point (95% CI -0.05 to 0.33, p = 0.15, I
2 30%) with a Cohen’s d effect size of 0.14 [36].
Steps per day at last follow-up
Eleven trials [14, 16,17,18, 20, 23,24,25,26,27, 30] measured average total daily steps per day. At baseline, average steps per day were similar for the intervention and comparator groups (6704 and 6327 steps respectively). On average, women randomised to a physical activity intervention group achieved 435 (95% CI -0.5 to 870.6, p = 0.05, I
2 54%) more steps per day than comparators at last follow-up (Fig. S3). These results represent 4.4 and 12.9% reductions in daily steps for the intervention and comparator groups at last follow-up, respectively.
Steps per day at 24 to 30 weeks gestation (mid pregnancy)
Seven trials [14, 16,17,18, 24, 26, 27] measured total steps per day at mid pregnancy. The intervention group, on average, achieved 7299 steps per day with comparators averaging 6162, equating to an average mean difference of 449 more steps per day favouring the intervention group (95% CI 5.5 to 892.7, p = 0.05, I
2 35%) (see Fig. S4). These results convert into a 7.2% increase in daily steps and a 1% reduction for the intervention and comparator groups accordingly.
Moderate-to-vigorous intensity physical activity at last follow-up
Six trials [16, 19, 22, 26, 28, 29] were included in the meta-analysis for mean minutes of MVPA per week. No significant differences were found between the intervention and comparator group at last follow-up for MVPA (95% CI -4.3 to 44.2, p = 0.11) (See Fig. S5).
Moderate-to-vigorous intensity physical activity at 24 to 30 weeks gestation (mid pregnancy)
Four trials [16, 26, 28, 29] were included in the meta-analysis for mean minutes of MVPA per week. at mid pregnancy. At baseline, average MVPA minutes per week were similar for the intervention and comparator groups (140 and 129 minutes, respectively). On average, those randomised to a physical activity intervention group achieved 34.2 minutes (95% CI -0.5 to 68.9, p = 0.05, I
2 53%) more MVPA per week than comparators at mid pregnancy (Fig. S6). These results represent a 12.8% increase for intervention and 16.3% reduction for the comparator group compared to baseline.
Gestational weight gain
A total of 12 [14,15,16,17, 21,22,23,24,25,26,27, 29] of the included trials also measured gestational weight gain (kg). The average baseline weight for women in the intervention and comparator groups were 80.2 kg and 80.3 kg, respectively. Women randomised to a physical activity intervention group on average gained 0.69 kg less weight than comparators at last follow-up (95% CI -1.30 to -0.08, p = 0.03, I
2 38%) (See Fig. 3). Women randomised to a physical activity intervention group and weighed at < 36 weeks [17, 21, 23, 24, 26, 27, 29] gained 0.58 kg (95% CI -1.07 to 0.09, p = .02, I
2 0%) less weight than comparators, and those weighed at ≥36 weeks [14,15,16, 22, 38] gained 0.78 kg (95% CI -2.12 to 0.73, p = 0.34, I
2 61%) less weight than comparators. See Fig. S7.
Risk of bias
All 18 trials were analysed for RoB. A total of 12 trials (66.7%) were at a high RoB, 4 (22.2%) of some concern, and 2 (11.1%) a low RoB (see Fig. S8). The main high RoB came from the measurement of the outcome (n = 9), with eight trials not reporting how long participants wore the physical activity measurement device for (e.g., valid wear time) and/or the threshold for the minimum amount of valid device wear to be included in the analyses. Additionally, when considering selection of the reported result, 14 studies were found to be of some concern because there was no previous publication of a specified analysis plan. For the five domains of the RoB2, the value for Cronbach’s Alpha was α = .66.