Third-trimester exercise may influence labor timing

Third-trimester exercise may influence labor timing | Image Credit: © Alik Mulikov - © Alik Mulikov - stock.adobe.com.

There is a link between physical activity in the third trimester and the time of labor onset, according to a recent study published in Revista da Associacao Medica Brasileira.¹

Health benefits and complexity of labor timing

Physical activity during pregnancy has been linked to multiple health benefits, including reduced risks of excessive weight gain, gestational diabetes and hypertension, and cesarean section. However, the timing of labor is influenced by multiple complex interactions between the fetus, mother, and placenta.²

“There are limited reports investigating the association between physical activity and the time of labor onset in term pregnancies,” wrote investigators. “Conflicting results have been reported in these studies.”¹

Pregnant women often perform less leisure-time physical activity during pregnancy. Therefore, investigators conducted a cross-sectional study to evaluate the link between physical activity during pregnancy and the time of labor onset.

Assessing physical activity in pregnancy

Participants included women with low-risk pregnancies delivering at 37-weeks’ gestation or later completing the Pregnancy Physical Activity Questionnaire (PPAQ). High-risk pregnancies were excluded from the analysis, alongside those with delivery before 37-weeks’ gestation or to women who did not volunteer or speak Turkish.

Medical records were assessed for demographic and clinical characteristics, while the PPAQ was used to obtain self-reported type, duration, and frequency of physical activities. The last menstrual period and ultrasonography findings were also reported to determine women’s gestational age.

The PPAQ used metabolic equivalent of task (MET) values, with a MET value under 1.5 indicating sedentary activity, 1.5 to 3 light-intensity activity, 3 to 6 moderate-intensity activity, and vigorous activity over 6. The time spent on an activity was multiplied by its intensity to determine the energy expenditure (MET-h.wk-1).

Participant grouping and analysis

Cases included women delivering at 41-weeks’ gestation, while those delivering from 37- to 40-weeks’ gestation were labelled controls. Comparisons between groups included physical activity levels and average MET-h.wk-1 expended.

There were 260 women included in the final analysis, 94 of whom delivered at 41-weeks’ gestation or later and 166 delivered between 37- and 40-weeks’ gestation. A similar median age and body mass index were reported between groups, while nulliparity rates were 54.3% and 21.7%, respectively, and median gestational weight gain 10.50 and 10, respectively.

Cases also had a higher cesarean delivery rate than controls, at 27.7% and 6.6%, respectively. Additionally, these patients had a higher median sedentary activity level and a lower median moderate-intensity activity level and median household activity level.

Optimal cutoffs for delayed labor

Investigators identified 35.70 MET-h.wk-1 as the optimal sedentary activity cutoff level to predict birth at 41 weeks’ gestation or later, with an area under the curve (AUC) of 0.712. This value had a sensitivity of 67.1% and a specificity of 60.1%

For predicting birth under 41 weeks, the cutoff for moderate-intensity activity was 64.02 MET-h.wk-1, with an AUC of 0.584. This value had a sensitivity of 60.4% and a specificity of 57.8%.

Associations with delivery route and implications

A link was also reported between the level of physical activity in the third trimester and delivery route, with a higher level of median occupational activity in women delivering vaginally vs through cesarean section. In a multiple logistic regression analysis, an odds ratio of 1.03 was reported from sedentary activity for birth at 41 weeks’ gestation or later.

These results indicated a link between physical activity level in the third trimester and gestational age at birth. The data highlighted a delayed onset of labor from increased moderate-intensity and household activities alongside reduced sedentary activities.

“The physical activity level in the third trimester was also associated with the delivery route,” wrote investigators. “Women who gave birth vaginally had lower levels of sedentary activity and higher levels of occupational activity than women who underwent a cesarean section.”

1. Kinay T, Mert SA, Karadeniz RS, Ustun YE. Association between the physical activity level in the third trimester of pregnancy and the gestational age at birth. Rev Assoc Med Bras (1992). 2025;71(3):e20241509. doi:10.1590/1806-9282.20241509
2. Casey ML, MacDonald PC. Biomolecular processes in the initiation of parturition: decidual activation. Clin Obstet Gynecol. 1988;31(3):533-52. doi:10.1097/00003081-198809000-00005