Changes in physical activity across pregnancy among Chinese women: a longitudinal cohort study

Physical activity (PA) is bodily movement produced by skeletal muscles that requires energy expenditure, including activities undertaken while working, playing, carrying out household chores, travelling, and engaging in recreational activities [1]. PA during pregnancy is not only safe [1, 2] but also helpful in improving physical health, controlling weight, alleviating back pain, accelerating postpartum recovery and reducing the risk of gestational diabetes, preeclampsia and operative delivery, as well as relieving depression and anxiety [3‐16]. To achieve good health, the World Health Organization (WHO) recommends that adults engage in at least 150 min of moderate-intensity PA throughout the week or an equivalent form of PA that achieves at least 600 metabolic equivalent task (MET) min/week [1, 17]. Pregnant women are advised to maintain the same level of PA as non-pregnant women [18‐20].

Successful intervention for PA requires understanding PA level across pregnancy and its correlates. Previous studies have shown that PA tends to decrease during pregnancy compared with the prepregnancy period [21, 22]. The proportion of pregnant women achieving the recommended PA level varies widely from 11–66% worldwide, and this wide range is mainly due to different population characteristics and assessment times [22‐24]. Few studies have investigated changes in PA over the course of pregnancy, and the results have varied [13, 25, 26]. The results of studies on the association of population characteristics (e.g., demographic, pregnancy and health characteristics) with PA during pregnancy vary [26‐29]. Higher educational level, higher income, employment and greater pre-pregnancy PA are reported to be associated with higher PA level [26, 27], while multiparity and unpleasant pregnancy symptoms are associated with less PA [28]. The influence of body mass index (BMI) on PA is mixed [28, 29].

Chinese families attach high importance to pregnant women and their foetuses and adhere to the traditional philosophy of protecting the foetus from miscarriage by advising pregnant women to rest as much as possible [30]. Despite this tradition, young women are accepting of modern healthcare-based recommendations and actively engage in PA. PA among Chinese women is sparsely studied. The proportion of pregnant women meeting PA recommendations varies from 11% in Tianjin [24] to 57.1% in Chengdu [25]. However, these studies are limited by their cross-sectional natures and represent only one city or district of China [24, 25].

Therefore, our study aims to investigate PA changes between early and mid-to-late pregnancy and the association of population characteristics with PA changes among Chinese women. Our study was based on the Chinese Pregnant Women Cohort Study-Peking Union Medical College (CPWCS-PUMC). The CPWCS-PUMC is a multicentre prospective observational study designed to investigate the lifestyles of pregnant Chinese women and the associations between lifestyle and obstetric or neonatal outcomes.

To our knowledge, this is the first multicentre longitudinal cohort study to investigate changes in PA across pregnancy in a Chinese population. We found that PA levels increased from early to mid-to-late pregnancy and that more than half of the women eventually had sufficient PA as recommended. Walking was the dominant form of PA. Women with sufficient PA levels in early pregnancy were more likely to maintain or achieve sufficient PA across their pregnancies. PA levels varied in different regions of China, with women in the West being most likely and those in the Central being least likely to have sufficient and increasing PA. Habitual smoking was inversely associated with sufficient and increasing PA. Women with higher educational levels were less likely to decrease PA across pregnancy.

Our study found that the proportion of pregnant women achieving the recommended PA level increased from 32.72% in early pregnancy to 55.25% in mid-to-late pregnancy. Studies investigating PA levels at different pregnancy stages are limited. In contrast to our study, studies of western populations showed that PA decreased or remained unchanged as pregnancy progressed [39, 40]. Regarding studies with Chinese populations, the proportion of women achieving the recommended level remained at a low level of 11% across the pregnancies of urban women from Tianjin [24] and increased from 53.8% in the first trimester to 61.4% in the third trimester among women from Chengdu [25]. But both of these studies were cross-sectional, and the changes in PA were concluded from different subsets of women. Our study was a multicentre study, and PA was surveyed in the same sample of women longitudinally at different pregnancy stages, resulting in a better representation of the Chinese population and in less bias. However, women who declined to participate in the PA assessment or could not recall PA level when being surveyed were not included in our final analysis. We found that women who completed the two PA assessments were more likely to have the characteristics that were reported to be positively associated with PA, such as a higher educational level. There might be a potential bias in that the women included in the study were those with a higher PA level. This might be part of the reason why our population had increasing PA across pregnancy. As the pregnancy progressed, the fear of miscarriage and the unpleasant pregnancy symptoms were gradually alleviated, which might also contribute to the resume of PA in mid-to-late pregnancy.

Our findings were consistent with those of one previous study using the IPAQ-SF, namely, that PA with medium or higher intensity contributed less to TEE during pregnancy [22]. Our study found that walking was the dominant form of PA. In this study, walking included all walking, namely, walking related to occupation, transportation, the household, exercise and leisure. Walking is the form of moderate-intensity PA indicated by the WHO recommendation and the form of exercise recommended by the American College of Obstetricians and Gynaecologist (ACOG) during pregnancy [1, 2, 17]. Chinese culture holds tight to traditional concepts of not walking fast, not running and not jumping during pregnancy, but walking is not restricted [30]. Therefore, it may be more reasonable and easier for prenatal healthcare providers to encourage women to walk appropriately to meet the sufficient level of 600 MET min/week than to persuade them to participate in other forms of PA.

It has been well documented that prepregnancy PA habits are strongly associated with PA levels during pregnancy [39, 40]. Our study found that women with sufficient PA levels at baseline were more likely to maintain or achieve sufficient PA across their pregnancies, further validating the fact that a good lifestyle is beneficial in the long term.

There were significant differences in the population characteristics among the three regional groups. Women in West China were more likely to have features favouring PA, such as a higher educational level, employment with a manual occupation and nulliparity, which may explain why they were more likely to have sufficient and increasing PA. The higher proportion of individuals of non-Han ethnicity may also play a role. Our results were consistent with one previous study reporting high and increasing PA across pregnancy in Chengdu, which located in West China [25]. One study conducted in Tianjin, which located in East China, found low and unchanged PA across pregnancy [24]. However, their study was limited by having only urban participants in one city. More studies are required to clarify the regional difference in PA.

Among the other correlates investigated, a history of smoking was inversely associated with sufficient and increasing PA. The findings were consistent with other study data showing that smokers had a more sedentary lifestyle [36]. The combined risk of smoking and low PA levels may make women more vulnerable to adverse pregnancy outcomes.

A recent systemic review revealed that younger age, higher educational level, higher income, employment, nulliparity, and normal weight were positively associated with PA during pregnancy, but the correlations were weak [39]. However, our study found that except for educational level, these factors were not associated with changes in PA across pregnancy. In our study, women with higher educational level tended to maintain sufficient PA throughout the whole pregnancy.

There were several limitations in our study. First, the study might have bias due to the self-report measure used to assess PA. Second, the generalization of our results may be limited to convenience sampling. Third, our study population may have a higher PA level since only those who agreed to participate and could recall PA were finally included in the analysis. Fourth, the large time frame within which PA was surveyed (especially the second survey) was partly responsible for the large range of PA level. The difference in the time interval between two PA assessments may have an influence on the result of the PA change across pregnancy. Finally, our study did not include pre-pregnancy PA level, discomfort during pregnancy and subjective factors, such as self-efficacy or perceived behavioural control, which might influence PA [29, 41]. Further analyses that include these factors as determinants of PA are needed.

To our knowledge, our study is the first multicentre longitudinal cohort study to investigate changes in PA across pregnancy among Chinese women. Our findings indicated that PA increased as pregnancy progressed, and that walking was the dominant form of PA. Further research is needed to better understand correlates of PA change and develop appropriate interventions for PA to improve maternal health among Chinese women.