The effect of exercise on maternal complications and birth outcomes in overweight or obese pregnant women: a meta-analysis

Introduction

The incidence of overweight and obesity has risen significantly in the last several decades. From 1980 to 2013, overweight and obesity has increased about 10% in women globally (1). Approximately 1 in 4 women are overweight after childbirth and 1 in 5 women are obese before pregnancy (2). Women of childbearing age should therefore strengthen their nutrition during this special physiological process. The lack of nutritional knowledge and blind supplementation can not only result in unnecessary obesity, but can also cause nutritional imbalances, and result in unnecessary risks to pregnancy and delivery (3-5).

Overweight or obesity can increase the risk for adverse obstetric outcomes, which may increase the risk of neonatal mortality (6,7) as well as gestational hypertension (GH), preeclampsia, gestational diabetes, cesarean delivery, neonatal intensive care unit admission, extended length of hospital stays, large for gestational age infants, and neonatal asphyxia (8-11). In addition, children born to obese pregnant women have a relatively higher risk of cardiovascular disease in later life compared to those born to normal weight women (12,13).

Pregnancy-induced hypertension is one of the most common pregnancy complications, which causes serious damage to the heart, brain, kidney, liver, and other important organs in pregnant women, and poses a significant threat to mothers and infants (14-16). The increased blood glucose of overweight or obese pregnant women leads to an increase in fetal blood glucose and an increase in insulin secretion by fetal islet β cells stimulated by fetal hyperglycemia (17-20). Fetal insulin mainly promotes fetal growth and promotes weight gain, which may lead to macrosomia.

Exercise is universally acknowledged as a way to stay healthy and to reduce pregnancy complications and adverse birth outcomes by promoting weight loss or preventing weight gain (21). However, the impact of exercise on overweight and obese pregnant women is controversial.

There are several articles analyzing the association between overweight and obesity in pregnancy with pregnancy complications and birth outcomes, in which there exist various research designs, recruitment and exclusion criteria, methods, and results. Davenport et al. (22) performed a meta-analysis in 2018 which contained all study design with considerable heterogeneity. For the reason, a meta-analysis was performed in this study only included randomized controlled trials to evaluate the effect of exercise on pregnancy complications and birth outcomes in overweight or obese pregnant women. We present the following article in accordance with the PRISMA reporting checklist (available at http://dx.doi.org/10.21037/apm-20-2097).

Methods

Searched databases and strategies

We searched PubMed, Cochrane Library, Embase, and Web of Science using the terms “pregnancy” combined with “obese” or “overweight” and “complications” or “outcome” and “exercise” between January 1974 and January 2020. Two independent investigators conducted a preliminary survey, deleted duplicate records, screened the relevance of titles and summaries, and determined which publications were excluded or required further assessment. We then reviewed the full text for inclusion. We also manually checked the references of the retrieved articles and previous reviews to identify additional eligible studies. In order to obtain more relevant research and higher accuracy, the reference list of each article retrieved was also reviewed.

Inclusion and exclusion criteria

Studies were included if:

• They were randomized controlled trials (RCTs);
• Studied the effect of exercise for overweight or obese pregnant women;
• Involved no less than one evaluation indicator;
• English language only.

Studies were excluded if:

• They were case studies/meta-analyses/letter to editors;
• Included patients with other diseases;
• Duplicate publications

The Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework was used to assess the quality of included studies. Accordingly, evidence from RCTs was considered high quality.

Data extraction and review

Two reviewers independently extracted the data and full text. For each study, the data collected included date of publication, first author, nation, number of patients enrolled and randomized in each study, age (years), recruitment gestational week and BMI, and intervention measures and outcomes. Literature quality of RCTs was assessed using the Jadad score, where a score of 1–2 was low quality, and a score of 3–5 was high quality.

Evaluation indicator

Gestational diabetes, GH, preeclampsia, cesarean delivery, gestational weight gain (GWG), gestational length at delivery, preterm delivery, Apgar score at 1 and 5 minutes, macrosomia, and neonatal asphyxia were extracted as the evaluation indicators in this study.

Statistical analysis

Statistical software Stata (SE) 11.2 was used to analyze the selected literature. A heterogeneity test was conducted before data consolidation. If P>0.05 or I²<50%, the data was considered to be homogeneous, and the fixed effect model was adopted; otherwise, the random effect model was adopted. The count data were represented by relative risk (RR) as the effect quantity, and the measurement data were represented by standard mean difference (SMD), both of which gave 95% confidence intervals (CI). Publication bias was concomitantly examined by Begg’s test.

Results

Search results

The electronic database search resulted in a total number of 811 articles. After thorough review, 13 papers (23-35) eventually met all inclusion criteria. The other 798 articles were excluded due to repetition, irrelevant studies, no control groups, incomplete data or comparisons, other operations, reviews, and incomplete articles. Figure 1 is a flowchart of identification, inclusion, and exclusion, reflecting the search process and the reasons for exclusion. Of all the included studies, the Jadad scores of 11 studies were equal to or greater than 3, and the other 2 papers were of low quality.

Figure 1 Flow diagram of the search process, study identification, and study inclusion and exclusion.

Main features of the studies

Table 1 summarizes the characteristics of the included studies. This analysis consisted of a total number of 1,709 patients. All articles were published from 2009 to 2017. This study included 859 patients in the exercise group and 850 patients in the control group.

Table 1 Characteristics of the included studies
Full table

Results of the meta-analysis

Meta-analysis on GWG

A total of 12 studies with 709 patients in the exercise group and 696 patients in the control group involved GWG. Figure 2 shows the forest plot of the summarized results. All 12 studies showed significant differences in GWG between the 2 groups (SMD =−0.21, 95% CI: −0.32–−0.10, P<0.001; P for heterogeneity =0.075, I²=39.9%). GWG in the exercise group was significantly lower compared to the control group.

Figure 2 Forest plot for gestational weight gain (GWG) in the exercise group and the control group. SMD, standard mean difference.

Meta-analysis on gestational diabetes

The forest plot for the meta-analysis on gestational diabetes is presented in Figure 3. The results demonstrated no significant differences between the exercise group with 794 patients and the control group with 786 patients (RR=0.71, 95% CI: 0.48–1.04, P=0.081; P for heterogeneity =0.004, I²=63.1%, the random effect model was adopted).

Figure 3 Forest plot for gestational diabetes in the exercise group and the control group. RR, relative risk.

Meta-analysis on GH

A total of 6 studies involved data on GH. The forest plot for the meta-analysis on GH is shown in Figure 4. The occurrence of GH in the exercise group (428 patients) was lower than that in the control group (424 patients) (RR=0.53, 95% CI: 0.32–0.88, P=0.014; P for heterogeneity =0.386, I²=3.7%).

Figure 4 Forest plot for gestational hypertension (GH) in the exercise group and the control group. RR, relative risk.

Other results

Meta-analysis results for other evaluation indicators are shown in Table 2. The meta-analysis results of other indicators including preeclampsia, cesarean delivery, gestational length at delivery, preterm delivery, Apgar score at 1 and 5 minutes, macrosomia, and neonatal asphyxia in the exercise group were similar to those of the control group.

Table 2 Meta-analysis results for the other evaluation indicators
Full table

Sensitivity analysis

We analyzed the data after excluding studies one by one, and there was no significant difference between the statistical results after exclusion and those before exclusion, indicating that the research results were relatively stable and reliable (Figure 5).

Figure 5 Sensitivity analysis of gestational weight gain (GWG) in the exercise group and the control group. CI, confidence interval.

Bias analysis

All studies on GWG were included in the funnel plot. The results showed that the funnel plot had good symmetry and little publication bias (Figure 6). The result of Begg’s test suggested that no significant evidence of potential publication bias existed (z=0.48, P=0.631).

Figure 6 Funnel plot of publication bias in studies on gestational weight gain (GWG). SMD, standard mean difference.

Discussion

This meta-analysis of 13 RCTs including 1,709 women showed that exercise in overweight or obese pregnancies could reduce GWG by 0.21 kg, and lower the risk of GH by 47%. However, there was no significant effect of exercise on other important clinical maternal and infant outcomes including gestational diabetes, preeclampsia, cesarean delivery, gestational length at delivery, preterm delivery, Apgar score at 1 and 5 minutes, macrosomia, and neonatal asphyxia.

Excessive GWG has been reported to increase the risk of poor prognosis for pregnancy outcomes, which may result in detrimental consequences for both maternal and infant health (4,36). Previous studies report a generally positive effect of exercise on GWG in pregnant women, although results differ between studies. A meta-analysis conducted by Streuling et al. concluded that exercise reduced GWG by 0.61 kg in pregnant women (37), while Du et al. demonstrated that physical exercise reduced GWG by 1.14 kg (38). This is consistent with our results, demonstrating a 0.21 kg reduction through exercise during pregnancy.

Several previous studies or systematic reviews and meta-analyses have reported the effect of exercise on gestational diabetes, however, the results are inconclusive. A meta-analysis found that physical exercise significantly reduced the risk of gestational diabetes (39) (RR=0.69, 95% CI: 0.52–0.91), and other studies found that exercise could lower the risk of gestational diabetes by 39% (40) and by 29% (38) in overweight and obese pregnant women. Nevertheless, some previous studies have demonstrated contrasting results (41,42), consistent with the results in our study, no significant differences between the exercise group and the control group on gestational diabetes incidence. Due to the heterogeneity in diagnostic criteria for gestational diabetes among studies, this discordance could influence the pooled effect.

Contrary to the negative results of several studies focused on exercise for overweight or obese pregnant women (41-43), the present study found a significant reduction in the risk of GH in the exercise group compared to the control group (RR=0.53, 95% CI: 0.32–0.88). This way of movement is simple, economical, and most pregnant women can perform, hence, exercise should be actively promoted during pregnancy.

With respect to results regarding other complications and infant outcomes, we did not observe any differences between the exercise group and the control group. A meta-analysis showed that supervised prenatal exercise reduced the risks of large for gestational age and macrosomia without an increased risk of small for gestational age (21), and another recent meta-analysis found that exercise reduced the risk of preterm birth by 38% (RR=0.62, 95% CI: 0.41–0.95) (40). Our current study found no significant effect of exercise during pregnancy in overweight or obese pregnant women on preeclampsia, cesarean delivery, gestational length at delivery, preterm delivery, Apgar score at 1 minute and 5 minutes, macrosomia, and neonatal asphyxia, which is consistent with other studies (13,44,45).

This study has some limitations. Firstly, it is difficult to maintain consistency across exercise patterns, duration, and intensity across the original included studies. Secondly, the baseline BMI was inconsistent across all studies. In addition, selection bias might have been introduced due to the inclusion of articles only published in English.

In conclusion, current evidence shows that exercise therapy has a beneficial effect on pregnancy complications and outcomes in overweight or obese pregnant women, and can effectively reduce the occurrence of GH and GWG. We may suggest that aerobic exercise for 30 min to 1 hour, three times a week may be beneficial to pregnant women. However, there is insufficient evidence to support superior birth outcomes, requiring further well-designed clinical studies to explore the relationship between exercise and pregnancy complications and birth outcomes in the future.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at http://dx.doi.org/10.21037/apm-20-2097

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/apm-20-2097). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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