Abstract
Background
Although studies have shown that physical activity may have protective effects against depression during pregnancy, evidence on the role of objectively measured physical activity remains limited. This study aimed to explore the associations between daily step counts in the second trimester and depressive symptoms at different stages of pregnancy.
Methods
Based on 828 pregnant women from the Ruian Birth Cohort Study, daily step counts were averaged over a week from WeChat records in the second trimester. Linear and logistic regression models were used to evaluate associations of daily step counts in the second trimester with Edinburgh Postnatal Depression Scale (EPDS) scores and clinically significant depressive symptoms (EPDS scores ≥ 10) in the second and third trimesters, respectively.
Results
The 828 pregnant women took an average of 3,840 (± 2,170) steps each day in the second trimester. Higher daily step counts were associated with lower EPDS scores in both the second (a unit of 1000 steps; β: -0.16, 95% CI: -0.30 to -0.03) and third trimesters (β: -0.25, 95% CI: -0.40 to -0.10). Additionally, higher step counts correlated with lower odds of clinically significant depressive symptoms in the third trimester (OR: 0.88, 95% CI: 0.79 to 0.96). The benefits were consistent across weekends and workdays.
Conclusion
Distinct patterns of association between second-trimester daily step counts and depressive symptoms in the second and third trimesters highlight the potential mental health benefits of maintaining higher daily step counts. The accessibility and high user engagement make daily step counts as a particularly practical tool for monitoring physical activity during pregnancy.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12889-025-24181-2.
Keywords: Physical activity, Step counts, Depressive symptoms, Pregnancy, Cohort study
Background
Antenatal depression is a common mental health issue, impacting approximately 20% of pregnant women worldwide [1]. This mood disorder is directly linked to increased risks of gestational hypertension and preterm birth, and it also affects fetal brain development through changes in maternal cortisol levels [2]. Therefore, it is essential to identify objective, measurable behaviors or interventions to prevent and treat antenatal depression.
Physical activity is a potential option for pregnant women to prevent depression and anxiety during pregnancy [3]. Previous studies have explored the relationship between physical activity and depression symptoms during pregnancy. Some suggest that physical activity could be an effective treatment for women at risk of antenatal depression [4, 5]. Similarly, other studies suggest that physical activity may serve as a feasible non-pharmacological intervention to reduce postpartum depressive symptoms [6, 7].
The number of steps taken each day is a simple and quantifiable indicator of physical activity [8]. It is particularly suitable for pregnant women who are worried about the risks of intensive physical activity and live in environments without exercising equipment [9]. Moreover, with the widespread use of step-tracking technology in smartphones, monitoring daily step counts has become easier [10]. Although numerous studies have examined the association between daily step counts and depression in the general population [11], there is no research that specifically investigated how daily step counts during pregnancy affect depressive symptoms at different stages of pregnancy. Given the dynamic physiological and psychological variations that occur during pregnancy, it is essential to understand this relationship for developing effective strategies to improve maternal mental health throughout the entire pregnancy period.
Based on the Ruian Birth Cohort Study (RBCS), this study employed smartphone-recorded daily step counts in the second trimester and repeated assessments of depressive symptoms using the Edinburgh Postnatal Depression Scale (EPDS) in both the second and third trimesters. This study uniquely examined how daily step counts in the second trimester are associated with depressive symptoms at different stages of pregnancy. By identifying distinct patterns of association over time, the findings may inform simple, accessible, and non-invasive strategies to support maternal mental health throughout pregnancy.
Methods
Study design and participants
Individuals were recruited to participate in the RBCS, which was established at the Third Affiliated Hospital of Wenzhou Medical University in Ruian City, Zhejiang Province, China. The RBCS is an ongoing longitudinal investigation that specifically examines the relationship between environmental exposures and the health of pregnant women and children. The women were invited to participate in this study when they came for a health examination from February 1, 2022, to December 31, 2023, at the Third Affiliated Hospital of Wenzhou Medical University. All procedures contributing to this work complied with the ethical standards of the Ethics Committee of the Third Affiliated Hospital of Wenzhou Medical University, Wenzhou, China on human experimentation and with the Helsinki Declaration of 1975, as revised in 2013. All procedures involving human subjects were approved by the Ethics Committee of the Third Affiliated Hospital of Wenzhou Medical University, Wenzhou, China (YJ2023002). All participants provided written informed consent. The criteria for inclusion were: (1) participants with the gestational weeks (GW) limited to the first trimester (GW ≤ 14) and second trimesters (GW 14–28) at the inception; (2) participants aged ≥ 18 years; (3) participants whose pregnancy was not achieved through assisted reproductive technology (ART); and (4) participants willing to give birth in the study hospital. Pregnancies conceived via ART were excluded due to their distinct maternal characteristics, increased risks of complications, and potential psychological stress, which may confound associations between daily step counts and mental health outcomes [12, 13]. Investigators were trained professionally to conduct face-to-face interviews with the participants, utilizing structured questionnaires to collect data on socio-demographic characteristics, lifestyles, health status, living environments, and reproductive histories (Supplementary 2). During the follow-up process, participants were repeatedly interviewed at four time points including the first trimester, the second trimester, the third trimester, and during the hospital admission for delivery (the predelivery stage). Besides, information on the physical examinations, clinical diagnosis and treatments throughout the pregnancy was obtained from the hospital information system.
Upon finalizing the criteria, 3,446 individuals were enrolled in RBCS at baseline. For this analysis, daily step counts recorded via smartphones were available for 1,016 participants during the second trimester. To reduce potential confounding effects from pre-existing mental health conditions, all included participants self-reported having no emotional or psychiatric disorders at enrollment. Participants who lacked depression scores in either the second or third trimesters (n = 188) were excluded. Ultimately, 828 participants were included in the final analysis (Supplementary 1 Figure S1).
Assessment of daily step counts
WeChat, one of the most popular socialmedia platforms in China, allows users to track their daily step counts [14]. The WeChat application automatically records step data through the built-in sensors of the phone, regardless of whether the app is active or running in the background [15]. Because step counts may be underestimated if participants did not carry their phones, such as leaving them on desks during short-distance movements, participants were specifically asked to keep their phones in their pockets or handbags during waking hours. During the face-to-face interview in the second trimester, participants who used WeChat on their cell phones were asked to present the daily step counts over the last week. Step counts were averaged separately for working days, weekend days, and the entire week. Participants, who provided daily step counts covering at least three days, including at least one weekend day, were retained for data analysis. While the 3–7 day monitoring window was selected to capture typical physical activity patterns during the second trimester when pregnancy-related discomfort is generally less pronounced, we acknowledge this period may not fully represent activity levels across the entire second trimester [16]. This observation window was chosen for two main reasons. Firstly, it minimizes participant burden through the WeChat platform’s passive data collection. Secondly, previous studies have shown that a 3-day accelerometer monitoring period can provide valid estimates of habitual activity [17, 18].
To test the validity of daily step counts recorded by WeChat, we conducted a pilot study in which seven pregnant women with the iPhone Operation System and commercial pedometers (ivole, AU–383, China) and another five with the Android Operation System and commercial pedometers collected the daily step counts for a week. It was found that daily step counts extracted from WeChat were highly correlated with the step counts from the commercial pedometers. The intraclass correlation coefficients were 0.92 (95% CI: 0.70–0.97) for the iPhone operating system and 0.86 (95% CI: 0.63–0.95) for the Android operating system (Supplementary 1 Figure S3, Supplementary 1 Figure S4). This supports the validity of WeChat step count data as a feasible and accurate measure of physical activity in pregnant women.
Outcomes
Among the pregnant women in this study, the Edinburgh Postnatal Depression Scale (EPDS), which is a self-report and widely used tool [19–21], was employed to quantify the depressive symptoms. Although the EPDS was originally developed for the postnatal period, studies have demonstrated its reliability and validity in identifying depressive symptoms in antenatal populations [22]. The EPDS scale consists of 10 items to assess the emotional state throughout the previous week. Each EPDS component consists of a four-point scale, ranging from 0 to 3. The overall score ranges from 0 to 30, with higher scores indicating a greater intensity of depressive symptoms. Clinically significant depressive symptoms (yes or no) were defined as a participant having EPDS scores ≥ 10, as reported previously [23]. We assessed and analyzed the participants’ depressive symptoms in the second trimester and repeated this measurement in the third trimester.
Covariates
The analysis adjusted for several covariates that could potentially influence the association between daily step counts and depressive symptoms. These included maternal age (continuous), body mass index (BMI, categorized using the Chinese standard < 18.5, 18.5 to < 24, and ≥ 24.0 kg/m2 [24]) before pregnancy, education (lower than bachelor’s degree, bachelor’s degree, and graduate level degree), annual household income (< 100, 100 to < 200, and ≥ 200 thousand Yuan), working status during pregnancy (yes or no), parity (0 or ≥ 1), season of depressive symptom assessment (Spring, Summer, Autumn, and Winter), and passive smoking during pregnancy (yes or no). Pregnancy complications and comorbidities were also considered (yes or no), including gestational diabetes mellitus, pre-gestational diabetes mellitus, gestational hypertension, chronic hypertension, and thyroid dysfunction during pregnancy. Missing values for covariates were addressed using random forest multiple imputation [25].
Statistical analyses
A statistical description of continuous and categorical variables was presented as mean (standard deviation [SD]) and frequency (percentage), respectively. Linear and logistic regression models were used to estimate associations of daily step counts with EPDS scores and clinically significant depressive symptoms, respectively. We analysed both crude models and adjusted models where covariates of maternal age, BMI before pregnancy, education, income, working during pregnancy, parity, season of depressive symptom assessment, pregnancy complications or comorbidities, and passive smoking during pregnancy were adjusted. Association analyses were separately performed using the continuous and tertiles (tertile 1 as a reference) of daily step counts. Restricted cubic splines were used to examine the non-linear associations between daily step counts and depressive symptoms. The daily step counts were further analysed by categorising them into workdays and weekends to examine potential differences in their associations with depressive symptoms. Besides, participants were categorised into four groups according to the change in patterns of clinically significant depressive symptoms from the second trimester to the third trimester: No symptoms–No symptoms (a reference), No symptoms–Symptoms, Symptoms–Symptoms, Symptoms–No symptoms. Multinomial logistic regression models were used to examine associations between daily step counts and trajectories of symptoms. As a sensitivity analysis, linear mixed models (LMMs) were employed to address the repeated measurement of depressive symptoms throughout the second and third trimesters. Marginal mean EPDS scores across the full range of daily step counts were then estimated to visualize the dose-response relationship.
All data analyses were conducted using the R program (version 4.2.2). The threshold for statistical significance was established at P values less than 0.05, using a two-sided test.
Results
Baseline characteristics of participants
As shown in Table 1, the average age at pregnancy for the 828 participants was 28.43 (± 3.52) years. Among the participants, 571 (69.0%) had a normal BMI before pregnancy, 613 (74.1%) had a bachelor’s degree or above, and 359 (43.4%) of families had an annual household income ranging from 100 thousand to 200 thousand yuan. 495 (59.8%) of the females were primiparous, and 230 (27.8%) were passive smokers while pregnant. 438 (52.9%) pregnant women work during their pregnancy. The average number of days for which step counts were monitored was 6.90 (± 0.15) days. The participants took an average of 3840 (± 2170) steps each day. In the second trimester, the average depression score was 5.41(± 4.26), in the third trimester, the average depression score was 5.15 (± 4.50). Compared with participants included in the present study, those excluded were elder, less educated, more passive smokers, and more primiparous (Supplementary 1 Table S1).
Table 1.
Demographic characteristics of the study population in the analysis (N = 828)
| Characteristics | Mean ± SD or n (%) |
|---|---|
| Maternal age (years) | 28.43 ± 3.52 |
| BMI before pregnancy (kg/m2) | |
| < 18.5 kg/m² | 117 (14.1) |
| 18.5–23.9 kg/m² | 571 (69.0) |
| ≥ 24.0 kg/m² | 138 (16.7) |
| Missing | 2 (0.2) |
| Parity | |
| 0 | 495 (59.8) |
| ≥ 1 | 285 (34.3) |
| Missing | 48 (5.8) |
| Maternal education | |
| Less than bachelor’s degree | 212 (25.6) |
| Bachelor’s degree | 600 (72.5) |
| Graduate level degree | 13 (1.6) |
| Missing | 3 (0.4) |
| Family annual income (thousand yuan) | |
| < 100 | 165 (19.9) |
| 100 − 200 | 359 (43.4) |
| > 200 | 282 (34.1) |
| Missing | 22 (2.7) |
| Passive smoking | |
| Yes | 230 (27.8) |
| No | 585 (70.7) |
| Missing | 13 (1.6) |
| Gestational age (weeks) | |
| the second trimester | 21.89 (4.29) |
| the third trimester | 34.01 (3.81) |
| Work during pregnancy | |
| Yes | 438 (52.9) |
| No | 386 (46.6) |
| Missing | 4 (0.5) |
| Monitoring duration (days) | 6.90 ± 0.15 |
| Daily step count (1000 steps) | 3.84 ± 2.17 |
| Daily step count on weekends (1000 steps) | 3.68 ± 2.65 |
| Daily step count on workdays (1000 steps) | 3.90 ± 2.27 |
| EPDS score | |
| the second trimester | 5.41 ± 4.26 |
| the third trimester | 5.15 ± 4.50 |
| Pregnancy complications or comorbidities | |
| Yes | 236 (28.5) |
| No | 549 (66.3) |
| Missing | 43 (5.2) |
|
Season of depressive symptom assessment (Second trimester) | |
| Spring | 159 (19.2) |
| Summer | 262 (31.6) |
| Autumn | 252 (30.4) |
| Winter | 155 (18.7) |
|
Season of depressive symptom assessment (Third trimester) | |
| Spring | 144 (17.4) |
| Summer | 157 (19.0) |
| Autumn | 261 (31.5) |
| Winter | 266 (32.1) |
Abbreviations: BMI body mass index, SD standard deviation, EPDS Edinburgh Postnatal Depression Scale
Associations of daily step counts with depressive symptoms
In the adjusted models, an inverse association was observed between daily step counts and EPDS scores in the second trimester (Table 2). Compared with participants who had tertile 1 of daily step counts, individuals at tertile 3 (β: −1.03, 95% CI: −1.69 to −0.27) had significantly lower EPDS scores. When daily steps were analyzed as a continuous variable, an increase of 1,000 daily steps was associated with a 0.16-point decrease in EPDS scores (β: −0.16, 95% CI: −0.30 to −0.03). The restricted cubic spline curve revealed an L-shaped relationship between daily step counts and EPDS scores (Pfor overall =0.004; Pfor non−linearity =0.017), with the nadir observed at approximately 5,362 steps per day (Fig. 1A). However, no significant association was observed between step counts and clinically significant depressive symptoms in this trimester (Fig. 1B).
Table 2.
Associations of daily step counts with depressive symptoms (N = 828)
| Depressive symptoms | Daily step counts (unit = 1000 steps) | ||||
|---|---|---|---|---|---|
| Tertile 1 (0.06 − 2.69) | Tertile 2 (2.69 − 4.44) | Tertile 3 (4.44 − 19.28) | P trend | Continuous (0.06 − 19.28) | |
| EPDS scores | β (95% CI) a | β (95% CI) a | β (95% CI) a | ||
| The 2nd trimester | |||||
| Crude model | Ref (0) | −0.55 (−1.26, 0.16) | −1.13 (−1.84, −0.42) | 0.001 | −0.18 (−0.32, −0.05) |
| Adjusted model | Ref (0) | −0.44 (−1.14, 0.27) | −1.03 (−1.69, −0.27) | 0.007 | −0.16 (−0.30, −0.03) |
| The 3rd trimester | |||||
| Crude model | Ref (0) | −0.59 (−1.34, 0.15) | −1.46 (−2.20, −0.71) | < 0.001 | −0.27 (−0.41, −0.13) |
| Adjusted model | Ref (0) | −0.43 (−1.18, 0.32) | −1.29 (−2.05, −0.53) | < 0.001 | −0.25 (−0.40, −0.10) |
| Clinically significant depressive symptoms | OR (95% CI) b | OR (95% CI) b | OR (95% CI) b | ||
| The 2nd trimester | |||||
| Crude model | Ref (1) | 1.00 (0.65, 1.54) | 0.71 (0.45, 1.11) | 0.090 | 0.94 (0.85, 1.02) |
| Adjusted model | Ref (1) | 1.07 (0.69, 1.67) | 0.74 (0.46, 1.19) | 0.201 | 0.95 (0.86, 1.04) |
| The 3rd trimester | |||||
| Crude model | Ref (1) | 1.00 (0.67, 1.51) | 0.47 (0.29, 0.75) | 0.003 | 0.86 (0.78, 0.95) |
| Adjusted model | Ref (1) | 1.08 (0.70, 1.65) | 0.53 (0.32, 0.86) | 0.014 | 0.88 (0.80, 0.97) |
Abbreviations: β coefficient, CI confidence interval, EPDS Edinburgh Postnatal Depression Scale, OR odds ratio
a Linear regression model was adjusted for maternal age, body mass index (BMI) before pregnancy, education, income, working during pregnancy, parity, season of depressive symptom assessment, pregnancy complications or comorbidities, and passive smoking during pregnancy
b Logistic regression model was adjusted for the same covariates as used in the linear regression model
Fig. 1.
Dose-response relationships between second-trimester daily step counts and depressive symptoms. A EPDS scores in the second trimester; B) Clinically significant depressive symptoms in the second trimester; C EPDS scores in the third trimester; and D) Clinically significant depressive symptoms in the third trimester. The method of restricted cubic splines with three knots was used to explore the relationships between daily step counts and EPDS scores, and clinically significant depressive symptoms, adjusting for maternal age, body mass index (BMI) before pregnancy, education, income, working during pregnancy, parity, season of depressive symptom assessment, pregnancy complications or comorbidities, and passive smoking during pregnancy. Abbreviations: CI, confidence interval; EPDS, Edinburgh Postnatal Depression Scale; OR, odds ratio
The inverse association persisted and became more pronounced in the third trimester (Table 2). Compared with participants who had tertile 1 of daily step counts, individuals at tertile 3 had significantly lower EPDS scores (β: −1.29, 95% CI: −2.05 to −0.53) and 47% lower odds of clinically significant depressive symptoms (OR: 0.53, 95% CI: 0.32 to 0.86). Similarly, in the continuous model, an increase of 1000 daily steps was associated with a 0.25-point reduction in EPDS scores (β: −0.25, 95% CI: −0.40 to −0.10) and 12% decrease in the odds of clinically significant depressive symptoms (OR: 0.88, 95% CI: 0.80 to 0.97). Dose-response curves supported linear relationships for both EPDS scores (Fig. 1C, Pfor overall =0.002; Pfor non−linear =0.311) and clinically significant depressive symptoms (Fig. 1D, Pfor overall =0.048; Pfor non−linear =0.823).
Crude models showed consistent results with comparable effect sizes and significance levels to adjusted models (Table 2).
Associations between weekend and workday step counts and depressive symptoms
Analysis of the average number of daily steps revealed that participants took more steps on workdays compared to weekends (Supplementary 1 Figure S2). After adjusting the covariates (Table 3), both weekend (β: −0.12, 95% CI: −0.23 to −0.01) and workday (β: −0.14, 95% CI: −0.27 to −0.01) step counts were inversely associated with EPDS scores in the second trimester. However, no significant association was observed between weekend or workday step counts and clinically significant depressive symptoms during this period.
Table 3.
Associations of weekend and workday step counts with depressive symptoms (N = 828)
| Depressive symptoms | Daily step counts (unit = 1000 steps) | |
|---|---|---|
| Weekend | Workday | |
| EPDS scores | β (95% CI) a | β (95% CI) a |
| The 2nd trimester | ||
| Crude model | −0.12 (−0.23, −0.01) | -0.16 (-0.29, -0.04) |
| Adjusted model | -0.12 (-0.23, -0.01) | -0.14 (-0.27, -0.01) |
| The 3rd trimester | ||
| Crude model | −0.20 (−0.31, −0.08) | −0.24 (−0.37, −0.11) |
| Adjusted model | -0.18 (-0.30, -0.07) | -0.21 (-0.35, -0.07) |
| Clinically significant depressive symptoms | OR (95% CI) b | OR (95% CI) b |
| The 2nd trimester | ||
| Crude model | 0.96 (0.89, 1.03) | 0.94 (0.86, 1.02) |
| Adjusted model | 0.97 (0.89, 1.04) | 0.95 (0.87, 1.03) |
| The 3rd trimester | ||
| Crude model | 0.86 (0.78, 0.93) | 0.89 (0.81, 0.97) |
| Adjusted model | 0.87 (0.80, 0.95) | 0.91 (0.83, 0.99) |
a Linear regression model was adjusted for maternal age, body mass index (BMI) before pregnancy, education, income, working during pregnancy, parity, season of depressive symptom assessment, pregnancy complications or comorbidities, and passive smoking during pregnancy
b Logistic regression model was adjusted for the same covariates as used in the linear regression model
The inverse associations persisted and became more pronounced in the third trimester. Higher step counts on both weekends and workdays were significantly associated with lower EPDS scores. Additionally, higher step counts on weekends were associated with 13% lower odds of clinically significant depressive symptoms (OR: 0.87, 95% CI: 0.80 to 0.95), while higher step counts on workdays were associated with 9% lower risk of clinically significant depressive symptoms (OR: 0.91, 95% CI: 0.83 to 0.99).
Association of daily step counts and trajectories of clinically significant depressive symptoms
As illustrated in Supplementary 1 Table S2, four distinct transition patterns of clinically significant depressive symptoms from the second to the third trimester were identified as mentioned above: No symptoms–No symptoms group (a reference), No symptoms–Symptoms group, Symptoms–Symptoms group, and Symptoms–No symptoms group. Compared with the reference group, participants with higher daily steps were less likely to transition from no symptoms in the second trimester to clinically significant depressive symptoms in the third trimester (OR: 0.84, 95% CI: 0.73 to 0.97).
Sensitivity analysis
To investigate the long-term cumulative effects of daily step counts on depressive symptoms during pregnancy, we conducted a sensitivity analysis using a linear mixed model that incorporated all available EPDS scores in the second and third trimesters, regardless of missing data at individual time points (Supplementary 1 Table S3). Compared with participants who had tertile 1 of daily step counts, those at tertile 3 had significantly lower EPDS scores (β: −1.21, 95% CI: −1.87 to −0.54). When modeled as a continuous variable, each additional 1000 daily steps was associated with a 0.21-point decrease in EPDS scores (95% CI: −0.33 to −0.08). Moreover, we estimated the marginal mean EPDS scores across the range of step counts. The marginal means revealed a clear downward trend in EPDS scores with increasing daily steps (Supplementary 1 Figure S5). These results were consistent with the primary findings, supporting the robustness of the association.
Discussion
This study is the first to investigate the longitudinal association between device-measured daily step counts and antenatal mental health, revealing distinct patterns between second-trimester step counts and antenatal depressive symptoms at different stages of pregnancy. We found that higher daily step counts in the second trimester are associated with lower EPDS scores during the same period. Moreover, increased step counts in the second trimester were linked to both reduced EPDS scores and lower odds of clinically significant depressive symptoms in the third trimester. By establishing time-specific and dose-dependent associations, it was found that higher daily step counts in the second trimester not only alleviate immediate depressive symptoms but may also benefit the longitudinal mental health throughout pregnancy.
The pattern of association between second-trimester step counts and second-trimester depressive symptoms
In the second trimester, we found an L-shaped association between step counts and EPDS scores, where EPDS scores declined with increasing steps up to approximately 5000 steps per day, but the effect plateaued beyond this threshold. Similar nonlinear trends have been reported in non-pregnant populations, where moderate step counts were most strongly linked to lower odds of clinically significant depressive symptoms, while high step counts demonstrated weaker associations [26]. This pattern aligns with the neurobiological threshold hypothesis [27]. Moderate step counts (≤ 5,000 steps per day) can induce rapid releases of brain-derived neurotrophic factor (BDNF), temporarily alleviating subclinical depressive symptoms captured by continuous EPDS scores [28]. Notably, even a single exercise session can rapidly elevate serum BDNF concentrations through peripheral metabolic mechanisms, providing immediate, though short-lived, mood benefits [29]. However, these acute benefits plateau beyond 5,000 steps, likely due to the counteracting effects of oxidative stress [30].
Although a similar trend observed with EPDS scores was noted, the association between daily step counts and the likelihood of clinically significant depressive symptoms (EPDS ≥ 10) in the second trimester did not reach statistical significance. This may be explained by the inherent limitations of the cross-sectional design [31], which captures only a single time point and may not reflect the longer-term biological processes required for depressive symptoms to surpass the clinical threshold. For instance, sustained BDNF elevation over six weeks or more is typically needed to improve hippocampal function [32]. Additionally, pregnancy-specific confounders, such as pregnancy-related symptoms, hormonal fluctuations, or sleep disturbances, may simultaneously reduce physical activity levels and exacerbate mood fluctuations, further obscuring the causal relationship between daily step counts and depressive symptoms [33].
Patterns of association between second-trimester step counts and third-trimester depressive symptoms
A linear protective effect emerged in the third trimester, with each 1,000 step increase associated with a 0.25 points reduction and 12% lower odds of clinically significant depressive symptoms. This linear relationship emphasizes the cumulative and delayed effects of step counts during pregnancy. While moderate daily steps may provide immediate mood benefits, sustained and gradual increases in step counts appear essential for long-term protection against depressive symptoms in late pregnancy. Several neurobiological mechanisms may explain this pattern, including BDNF expression regulation as well as oxidative stress [34–37]. Higher daily steps in the second trimester can gradually raise BDNF levels, forming a neuroprotective reserve that helps buffer the effects of elevated cortisol, typically seen in late pregnancy [38]. Additionally, regular steps in the second trimester can reduce levels of IL-6 over a period of weeks or more, thereby reducing oxidative stress in late pregnancy [39]. Beyond physiological mechanisms, maintaining a consistent step count routine may enhance self-efficacy, helping pregnant women to better manage body image concerns, sleep disturbances, and childbirth-related anxiety [40].
To assess the robustness of these findings, we further conducted a sensitivity analysis using linear mixed models that included all available EPDS scores across pregnancy, regardless of missing data. The results were consistent with the primary analyses. Therefore, encouraging pregnant women to gradually increase their daily step counts may have lasting psychological benefits that extend throughout the entire pregnancy.
Strategies for sustainable step count enhancement in pregnancy
Among the pregnant women in our cohort, only 196 (23.6%) engage in daily step counts of 5000 or more. To support mental well-being throughout pregnancy, women may benefit from gradually increasing their daily step count in ways that fit their lifestyle. Simple strategies such as taking short walks after meals, choosing stairs over elevators, or walking while talking on the phone can help incorporate more steps into daily routines. Those experiencing higher stress levels or lower social support may find it helpful to walk with a friend or partner, join a pregnancy-friendly walking group, or use step-tracking apps for motivation (Hoffman and Hatch, 1996 [41]. Additionally, setting realistic, achievable step goals, such as adding 1,000 extra steps per day, may provide both physical and mental health benefits [42].
Strengths and limitations
This study has several strengths. First, by using smartphone-based step tracking, we objectively captured the fragmented nature of physical activity in pregnant women, overcoming the recall bias inherent in traditional self-reported questionnaires. Second, the longitudinal study design allowed for a dynamic assessment of depressive symptoms across the second and third trimesters, revealing stage-specific differences in the association between step counts and depressive symptoms.
This study also has several limitations. First, as an observational study, causality cannot be inferred. While our results suggested that higher step counts may have protective effects against depressive symptoms, the potential for residual confounding and reverse causation remains. Second, reliance on smartphones may lead to underestimation of step counts, particularly during activities where the phone is not carried. Third, this study lacked step count data in the third trimester, preventing us from evaluating its changes over time or its potential cumulative effects on depressive symptoms. Finally, the generalisability of our findings may be limited by selection bias, as excluded participants were generally elder, less educated, and had lower incomes.
Conclusions
Physical activity during pregnancy is increasingly recognised for its potential role in promoting maternal mental health. Based on data from the Ruian Birth Cohort Study (RBCS), our study systematically explored the longitudinal association between step-based physical activity in the second trimester and depressive symptoms throughout pregnancy. We identified distinct patterns of association, with an L-shaped relationship in the second trimester and a linear relationship in the third trimester. While previous studies have often focused on exercise intensity or structured interventions, our findings suggest that even daily, unstructured patterns of physical activity, such as step counts, may be relevant to antenatal mental health. By identifying trimester-specific associations, this study contributes to the development of more tailored, time-sensitive approaches to physical activity promotion in pregnancy. The findings may help inform public health strategies and clinical guidelines for antenatal mental health care.
Supplementary Information
Acknowledgements
We thank the cooperation and support of RBCS participants for this study and appreciate the significant contributions made by relevant medical personnel, researchers, and investigators to this study.
Authors’ contributions
W.Z. had complete access to the data and assumes responsibility for its integrity and the accuracy of the analysis. W.Z., J.G. and G.C. wrote the study protocol; Q.M., P.C., W.D. and L.L. collected study data; Y.H., Y.Z., J.F. and C.T. analysed the data. W.Z. drafted the first version of the manuscript. L.L. and G.C. critically revised the manuscript. All authors have read and approved the final version of the manuscript, and agree with the order of presentation of the authors.
Funding
This study was supported by the National Natural Science Foundation of China Regional Innovation and Development Joint Fund (No. U22A20358), the Program of Zhejiang Provincial Program for the Cultivation of High-Level Innovative Health Talents (No. 2020-18), Wenzhou science and technology project of China (No. Y20220408).
Data availability
The data that support the findings of this study are available on request from the corresponding author (Guangdi Chen). The data are not publicly available due to the containing information could compromise the privacy of research participants.
Declarations
Ethics approval and consent to participate
All procedures contributing to this work complied with the ethical standards of the Ethics Committee of the Third Affiliated Hospital of Wenzhou Medical University, Wenzhou, China on human experimentation and with the Helsinki Declaration of 1975, as revised in 2013. All procedures involving human subjects were approved by the Ethics Committee of the Third Affiliated Hospital of Wenzhou Medical University, Wenzhou, China (YJ2023002). All participants provided written informed consent.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Wenyi Zhang and Qiuqiu Mu contributed equally to this work and should be considered joint first authors.
Guangdi Chen and Lin Lin contributed equally as corresponding authors.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author (Guangdi Chen). The data are not publicly available due to the containing information could compromise the privacy of research participants.