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Maternal obesity is associated with complications and adverse outcomes during the labor and delivery process. In pregnant women with a healthy body weight, maternal physical activity during pregnancy is associated with better obstetric outcomes; however, the effect of maternal physical activity during pregnancy on obstetric outcomes in obese women is not known. The purpose of the study was to determine the influence of self-reported physical activity levels on obstetric outcomes in pregnant obese women.
A retrospective chart review was performed on 48 active obese women and 48 inactive obese women (N=96) who received prenatal care and delivered at the medical center during the past five years. Obstetric and neonatal outcomes were compared between the active and inactive groups.
Obese women who were active during pregnancy spent less total time in labor (13.4 hours vs. 19.2 hours, p=0.048) and were less likely to request an epidural (92% vs. 100%, p=0.04). When stratified by parity, active multiparous women spent significantly less total time in labor compared to inactive multiparous (6.2 hours vs. 16.7 hours, p=0.018). There were no statistical differences between groups in rates of cesarean deliveries or neonatal outcomes.
Maternal physical activity during pregnancy appears to improve obstetric outcomes in obese women, and this improvement may be more pronounced among multiparous women. Our finding is of particular importance as pregnant obese women are at higher risk for adverse and delivery outcomes.
The medical and economic burden of obesity is a major public health concern. The prevalence of maternal obesity has dramatically increased with one in three women entering pregnancy obese1. Maternal obesity has been associated with a wide array of adverse maternal and neonatal outcomes2 including elevated risk for complications during the labor and delivery process including slower progression of labor, labor dysfunction, and medically necessary cesarean deliveries3,4.
Labor complications in obesity include increased total duration of labor5 and slower progression of the early part of the first stage of labor3,6,7. Prolonged time in labor increases the risk for a number of unfavorable outcomes such as operative deliveries, infections, and adverse neonatal outcomes8–10. Maternal obesity has also been associated with active labor dysfunction including arrest of dilation and fetal distress11, both of which contribute to the elevated rate of cesarean deliveries among obese women3,4.
In the United States, the rate of cesarean deliveries dramatically rose by 53% from 1996 to 2007, reaching 32% of all deliveries12. The public health impact of excess cesarean deliveries is substantial as cesarean deliveries are expensive and increase the risk for other morbidities such as severe bleeding, infections, painful scarring, blood clots, bowel obstructions, readmissions to the hospital, and longer-lasting pain4. With maternal obesity significantly elevating risk for cesarean deliveries, identification of methods to reduce the number of cesarean deliveries and improve the labor and delivery process for obese women is critical13.
In normal-weight women, regular physical activity during pregnancy has been shown to lower the incidence of cesarean deliveries14–17. Similarly, maternal physical activity during pregnancy in normal-weight women is associated with shorter active labors14,16. However, the influence of physical activity on the labor and delivery process and obstetric outcomes in women with pre-pregnancy obesity is not known. Therefore, the purpose of the study was to examine obstetric outcomes in pregnant obese women who self-reported being physically active during pregnancy versus pregnant obese women who did not. We hypothesized that maternal physical activity during pregnancy would reduce occurrence rate of cesarean sections in pregnant obese women. We secondarily hypothesized that physically active obese women would spend less total time in labor, less time pushing, and would have neonates with higher Apgar scores, healthier birth weights, and less incidence of neonatal complications.
A retrospective chart review was performed on women who received prenatal care at the Washington University School of Medicine’s Women’s Health Center between May 2009 and May 2014. All women treated at this clinic had private insurance, thus, it was considered a moderate-to-high income clinic. The patient’s age, weight, height, body mass index, race, parity, delivery history, gestational weight gain, and pregnancy complications were obtained from their prenatal charts. Pre-pregnancy body mass index (BMI) was determined by weight and height at their first prenatal appointment- typically between eight and nine weeks gestation. If a patient presented for care later than nine weeks gestation, pre-pregnancy weight was based on self-report. Physical activity information was gathered from health history questionnaires distributed by the clinic at initiation of prenatal care. Self-reported physical activity information was confirmed via personal telephone calls (at which time, participants provided informed consent to include their data in the study). If a woman was unable to confirm maintenance of questionnaire-reported physical activity levels (e.g. she reported she stopped exercising shortly after onset of pregnancy), that woman’s data were not included. During personal telephone calls, average frequency (number of times per week) and duration (length of typical sessions) of physical activity information was confirmed in order to calculate total minutes per week during their pregnancy. Mode of exercise was also confirmed via telephone calls. Information directly regarding the intensity of exercise was not collected, albeit mode (e.g. jogging vs. walking) does offer some information about intensity, and we suspect intensity may be more difficult to recall from physical activity session months or years ago compared to frequency and duration. Because the federal physical activity guidelines suggest 150 minutes of moderate physical activity per week18,19, 150minutes/week of structured/planned physical activity was used as the criteria for selecting physical activity for the study, and all reported activities have corresponding metabolic equivalent values that would classify them as at least moderate intensity20.
Delivery records were used to obtain mode of delivery, gestation age at delivery, type of labor (spontaneous, induced, or augmented), total time in labor, time in stage 2 of labor (pushing), and additional information regarding the labor and delivery process. Neonatal Apgar scores, birth weight, birth length, head circumference, cord blood gases, and nursery disposition were obtained from delivery records. Inductions included in the study were medically-indicated (i.e. hypertension, gestational diabetes, macrosomnia, intrauterine growth restriction, or post-dates).
Inclusions for the study included ages 18–44, pre-pregnancy BMI greater than or equal to 30kg/m2, viable pregnancy with no identified fetal abnormalities, and 37 weeks gestation or greater at admission to labor and delivery. Exclusions for the present study were multiple gestation pregnancy, diabetes mellitus prior to pregnancy, chronic hypertension prior to pregnancy, prior cesarean delivery or a scheduled cesarean delivery for the present pregnancy, and use of tobacco, illegal drugs, or alcohol during the pregnancy being studied.
For inclusion into the active group, patients had to report participating in physical activity for ≥150 min/week via clinic administered surveys at the initiation of prenatal care. Because these surveys were taken at the initiation of prenatal care, all women who met these criteria were called by the study team to confirm the maintenance of physical activity throughout pregnancy. If a woman reported a reduction in physical activity to <150min/week or cessation of physical activity during pregnancy, they were excluded from the study. More details regarding mode, duration, and frequency of exercise throughout the pregnancy were obtained during personal telephone calls as well. Inactive women were those who responded “no” to regular physical activity and met all other inclusion/exclusion criteria.
Based on previous data comparing rates of cesarean sections between active and inactive women with pre-pregnancy body mass indexes below 39 kg/m2 17, we estimated an effect size of 0.71. Therefore, with an alpha level of 0.05, 44 women per group (n=88) were required to power the study at β=0.90. Approval for this study was granted by the Washington University Institutional Review Board (IRB ID: 201405134).
Students T-Tests were used to compare continuous data between the two independent groups and chi-square tests were used to compare categorical data after testing for normality using Kolmogorov-Smirnov tests. Parity was used as a covariate (nulliparous versus multiparous) in analyzing total time in labor and time in stage 2 of labor as parity has a significant effect on these variables in previous studies21, as well as in our dataset (nulliparous women spent significantly more time in stage 2 than multiparous women regardless of physical activity levels, p<0.001). We also stratified our groups by parity in order to better understand the impact of physical activity on time in labor in exclusively nulliparous versus multiparous obese women. Type of labor (spontaneous, induced, or augmented) was also used as a covariate for analyzing total time in labor for inactive versus active groups as well as groups further stratified by parity. Relationships between amount of exercise (minutes per week) and obstetric outcomes were analyzed using Pearson Product Moment Correlation Coefficients for normally-distributed data and Spearman Rank Correlation Coefficients for non-normally-distributed data. All data analyses were performed with SPSS version 22, Armonk, NY. Statistical significance was defined as a p-value <0.05. Study data were collected and managed using REDCap electronic data capture tools22.
A total of 3120 pregnancies were screened for eligibility. For the obese active group, 98 pregnancies were identified as eligible, and 48 were reached via telephone and able to confirm physical activity throughout their entire pregnancy. For the obese inactive group, 48 pregnancies were identified. Demographic characteristics of the active versus inactive groups are reported in Table 1.
Demographic characteristics were similar between the groups. Reported modes of physical activity are reported in Table 2. Structured walking (83%) was the most commonly reported mode of physical activity.
When adjusted for parity and type of labor (spontaneous, augmented, induced), total time in labor was shorter in the active obese women when compared to the inactive obese women (p=0.048). When stratified by parity, there were no differences in total time in labor between active and inactive nulliparous pregnant obese women with type of labor (spontaneous, induced, augmented) used as a covariate (p=0.49). However, physically active multiparous women spent less total time in labor compared to inactive multiparous women (6.2± 3.8 hours in the active multiparous women versus 16.7 ±16.8 hours in the inactive multiparous women, p=0.018). Figure 1 shows time in labor stratified by parity. Amount of physical activity and parity were significantly associated (r=0.51, p=0.01).
Contrary to our hypothesis, rates of cesarean deliveries were similar between the two groups (25% in the active group versus 31% in the inactive group, p=0.49). Active women were less likely to request epidural anesthesia administration compared to the inactive group (92% vs. 100%, p=0.04). Active women were also less likely to require a cesarean delivery during stage two of labor (5% vs. 18%); however, the difference between groups did not achieve statistical significance (p=0.08). Labor and delivery outcomes are reported in Table 3. Table 4 shows indicators for the cesarean deliveries for both groups.
There were no statistically significant differences in pregnancy complications between groups. However, there were trends for active women to have lower rates of gestational hypertension or preeclampsia, polydraminos, fetal pylectasis, and meconium-strained amniotic fluid. Data on pregnancy complications are reported in Table 5.
Several trends in gestational weight gain between groups were noted. More active women met the Institute of Medicine (IOM) guidelines for gestational weight gain for obese women (11–20 pounds) when compared to inactive women (31% vs. 18%, p=0.09). Similarly, 62% of inactive women exceeded IOM guidelines for gestational weight gain compared to 48% in the active group (p=0.09).
There were no differences noted in neonatal Apgar scores, birth weight, birthweight percentiles for gestation age, birth length, head circumference, cord blood gases, or nursery disposition. Neonatal outcomes are shown in Table 6. Of note, amount of physical activity (minutes per week) and neonatal birthweight were significantly associated (r=0.48, p=0.02).
The main findings of our study were that active pregnant obese women spent less total time in labor and were less likely to request an epidural than inactive pregnant obese women. However, they were not less likely to undergo a cesarean delivery than inactive obese women. To our knowledge, this is the first study to demonstrate the positive benefits of maternal physical activity during pregnancy specifically on obstetric outcomes in obese women. In addition, several trends of importance were noted; active pregnant obese women were less likely to exceed IOM gestational weight gain guidelines and less likely to require a cesarean delivery during the stage two of labor (pushing); however, these results did not achieve statistical significance.
Obese women who were active during pregnancy spent significantly less total time in labor than women in the inactive group when adjusting for parity and whether labor was induced, spontaneous, or augmented. When stratifying groups further by parity, active multiparous women spent significantly less total time in labor compared to inactive multiparous women, suggesting that the influence of physical activity on time in labor is more pronounced after a woman’s first delivery. The mechanism for the beneficial impact of physical activity on time in labor in multiparous women and not nulliparous women in unclear and requires further study.
Based on the findings from this study, women who exercised at least 150min/week during their pregnancy spent less total time in labor compared to those who were inactive. However, no correlations between amount of physical activity (minutes per week) and obstetric outcomes were found. Taken together, these data suggest that 150 minutes of moderate physical activity may be a clinically significant threshold for reducing time in labor in obese pregnant women (as it is in non-pregnant populations for substantial health benefits18,19), and that there may not necessarily be a dose-response relationship between physical activity and time spent in labor in obese women as total time in labor and total minutes of physical activity per week were not significantly correlated.
Our primary finding is consistent with previous literature in normal-weight pregnant women that found physical activity during pregnancy to be associated with shorter active labors and shorter first stages of labor14,16,17. Prolonged time in labor contributes to compromised maternal and neonatal health and well-being (8–10). Prolonged labor increases the risk for operative delivery, cesarean delivery, and admission to the special care nursery; thus threatening survival and long-term neonatal health10. Prolonged labor may also increase the incidence of subsequent labor abnormalities, depressed Apgar scores, chorioamnionitis, need for newborn resuscitation, and postpartum pyrexia and sepsis8,9,23.
Aside from medical issues, prolonged labor may also lead to a negative birth experience24,25. The labor process can be physically and emotionally exhausting for the delivering woman, her support system, and the team managing her care26. Patients described long labor experiences as “severe pain that seemed to go on forever” and “suddenly failing or finding myself in a life-threatening condition”25. Therefore, prolonged labor may play a role in the decision to postpone future pregnancies due to fear or anxiety about going through labor delivery again24,25; Therefore, physical activity interventions that can reduce total time in labor should be considered; particularly in pregnant obese women who are already at increased risk for prolonged labor.
Although total time in labor was shorter in active obese women, we found no significant differences in stage two of labor between active and inactive groups. Therefore, the significantly reduced total time in labor in active obese women was the result of less time spent in stage one of labor. Thus, our study proposes that the previously reported impact of physical activity on time spent in stage one of labor in normal-weight women27 may translate to pregnant obese women, which is clinically important as length of labor appears to be longer in obese women3,6,7.
Contrary to our hypothesis, rates of cesarean deliveries were not different between active and inactive obese women. Our findings are consistent with a recent randomized clinical trial in obese pregnant women by Vinter et al. who found no differences in incidence of cesarean delivery between active and non-active women28. Interestingly, our study found a tendency for more inactive women to require their cesarean delivery during the process of pushing. We perceive the increased risk for a cesarean delivery during pushing in pregnant obese women as clinically meaningful as many women and physicians would agree that completing the first stage of labor, pushing for over an hour, and still requiring a cesarean delivery is an undesirable birthing process.
Epidural administration was significantly lower among pregnant women who were physically activity versus those who were not. Endurance activity in non-gravid runners has been linked to increased pain thresholds, coping strategies, and self-efficacy29, and physical activity during pregnancy in obese women has been associated with improved psychological well-being30. We suspect that physical activity during pregnancy may aid in pain tolerance, coping strategies, and in self-efficacy as it does in non-gravid individuals29, thus, providing a plausible connection between physically active obese women and lack-of requests for an epidural.
Overall, neonatal outcomes were not different between active and inactive obese pregnant women. However, a positive association between total physical activity and neonatal birthweight was found. This finding is consistent with Hatch et al. who found a positive association between exercise and birthweight in a group of 800 pregnant women. However, previous studies have also reported a negative association or no association between exercise and fetal growth31–34 (studies were not in exclusively obese women). Pivarnik suggests moderate physical activity may enhance birthweight, while more intense regimens may contribute in lighter offspring35. Our findings in obese women are consistent with this interpretation as women included in the present study were not part of an intensive exercise program, and all reported walking as their primary mode of exercise, which would be considered a moderate intensity activity.
A tertiary finding in the current study is that inactive obese women were more likely to exceed gestational weight gain guidelines for obese women as proposed by the IOM (48% in active group compared to 62% in the inactive group)36. These data are consistent with previous findings in non-obese women; active women gain less weight compared to inactive women37. Similarly, the incidence of gestational hypertension was not statistically significant between groups; however, the trend of lower rates of hypertension and/or preeclampsia in obese active women is consistent with findings in normal weight pregnant women17, and suggests activity may improve blood pressure during pregnancy in obese women.
The current study has several limitations. First, the study sample size was powered on our primary outcome which was rates of cesarean deliveries. Therefore, we may not have been adequately powered to detect statistical differences in secondary outcomes. Another limitation is that the primary independent variable- assignment to the active or inactive group- was based on self-report and not objective measurements. Therefore, study results should be carefully interpreted. Also, data regarding intensity of exercise sessions was not obtained; however, mode of exercise was established, and all reported modes of activity have generic metabolic equivalent levels that meet or exceed thresholds to be considered moderate intensity20. Next, our results may or may not be generalizable to a low-income population as all women included in this study were considered moderate-to-high income. Finally, labor initiation time for spontaneous labors was based on self-report (e.g. patients reported to the nurses what time they started experiencing labor-related contractions upon arrival to labor and delivery).
Active pregnant obese women spent less total time in labor than inactive obese women, and this difference was even more pronounced among multiparous obese women. Active obese women were less likely to request an epidural compared to inactive pregnant obese women. Collectively, our study suggests that physical activity can improve obstetric outcomes in pregnant obese women, and that 150min/week of physical activity may be a clinically relevant threshold for improving outcomes in obese pregnant women.
Funding: This publication was supported by the Washington University Institute of Clinical and Translational Sciences grants UL1 TR000448 and TL1 TR000449 from the National Center for Advancing Translational Sciences. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Conflicts of Interest: The authors have no conflicts of interest to disclose.