The Effect of Physical Activity During Pregnancy on Uterine and Fetal Parameters

Urbanization, rising living standards, and the comfort afforded by technological advances, characteristic of our age, are leading to the prevalence of physical inactivity. The potential effects of this on maternal and fetal health, especially during a sensitive period like pregnancy, pose a critical need for scientific research. The third trimester of pregnancy is a critical period during which fetal growth and development occur rapidly, and investigating the effects of physical inactivity on the fetus is of great importance.

In this study, physical activity levels during pregnancy will be determined using the Pregnancy Physical Activity Questionnaire (PPAQ) and daily step count. Fetal health parameters will include uterine blood flow markers (Resistance Index (RI), Systolic/Diastolic (S/D) ratio), fetal heart rate, and fetal birth weight. This study aims to make significant contributions to the literature by revealing the impact of physical activity levels on fetal health parameters in third-trimester pregnancies. Research Hypothesis:

This study will examine the effects of physical activity levels on fetal health parameters within the framework of the following hypotheses:

H1 (Research Hypothesis 1): It is hypothesized that fetal health parameters will be negatively affected in pregnant women who are physically inactive during pregnancy (e.g., impaired values, low birth weight).

H0 (Null Hypothesis 1): There is no statistically significant difference in fetal health parameters between pregnant women who are physically inactive during pregnancy and those who are active.

H2 (Research Hypothesis 2): It is hypothesized that fetal health parameters may also be negatively affected in pregnant women who are excessively physically active during pregnancy (e.g., impaired values, low birth weight), and that there is an optimal physical activity level for pregnancy.

H0 (Null Hypothesis 2): There is no linear relationship between physical activity levels during pregnancy and fetal heart rate and fetal health parameters, and excessive physical activity does not have a negative effect on these parameters. No specific studies have been found examining the relationship between physical activity level measured with the PPAQ and phone step count in the last trimester of pregnancy and uterine artery blood flow, fetal heart rate, and fetal birth weight. However, there are related research themes:

A study by Nguyen et al. found that moderate-intensity recreational physical activity was associated with a higher uterine artery pulsatility index and an increased risk of uterine artery notching. Conversely, moderate-intensity work activity was associated with a lower uterine artery pulsatility index and a reduced risk of uterine artery notching. No association was found with umbilical circulation (1). A study measured uterine artery blood flow in pregnant women and investigated its relationship with the mother's physical fitness level. This study showed that moderate, regular physical activity or inactivity in mothers during pregnancy did not affect resting uterine artery blood flow. In other words, no direct link has been found between the mother's physical fitness level and uterine blood flow. A randomized controlled trial on pregnancy activity examined the longitudinal effects of a supervised, moderate-intensity exercise program on uterine-placental and fetal blood flow parameters. The study observed no deterioration in fetal or maternal Doppler parameters in the exercise group. This suggests that the baby's health is not adversely affected by exercise.

A review on this topic has indicated that exercise during pregnancy can cause a temporary and harmless increase in fetal heart rate, which quickly returns to normal. It has also been revealed that uterine blood flow may decrease partially during exercise, but this is compensated for by physiological adaptations in the mother and quickly returns to normal, with little or no effect on fetal blood flow. The effects on birth weight vary across studies: some studies suggest that exercise may lead to lower birth weight, while others suggest no difference or that moderate-intensity exercise may have positive effects. This review emphasizes that strenuous exercise may increase the risk of low birth weight.

Furthermore, according to this review, if there are no obstetric or medical risks associated with exercise, pregnant women should be encouraged to engage in regular, moderate-intensity exercise programs. Beneficial exercises during pregnancy include walking, running/treadmill exercises, aerobics, swimming, and yoga. Extremely challenging sports and rapid immersion in water are not recommended during pregnancy. Pregnancy is not a prison, and healthy pregnant women should be encouraged to participate in and maintain physical activity.

This study will make a significant and original contribution to the literature because it is one of the first to assess the overall physical activity level of pregnant women, rather than the immediate effects of physical activity, and to measure fetal health parameters such as uterine artery blood flow, fetal heart rate, and fetal birth weight. While most existing research generally focuses on the short-term or acute effects of physical activity, this study aims to provide a more long-term and comprehensive analysis. In this context, physical activity level will be determined by Metabolic Equivalent of Task (MET) obtained through the Pregnancy Physical Activity Questionnaire (PPAQ). MET is a standard unit of measurement that indicates how much energy an activity expends compared to rest. Additionally, average step count data obtained from smartphones and watches will be used to assess overall physical activity levels.

Objective measurements of uterine artery blood flow will be made in the study. These measurements include parameters such as RI, which reflects blood flow resistance in the vessels. RI is the difference between systolic and diastolic velocity divided by systolic velocity. The S/D ratio will also be examined. Combining all these Doppler measurements with objective measurements such as fetal heart rate and birth weight will significantly increase the scientific value of the study.

The primary objective of this study is to determine the potential effects of a sedentary lifestyle on fetal health during the third trimester of pregnancy. This will contribute to the development of more informed recommendations for activity during pregnancy and the protection of maternal and fetal health. The data obtained will provide a scientific basis for healthcare professionals to better guide their clients.

Inclusion criteria

• Singleton pregnancy
• ≥28 gestational weeks (confirmed by ultrasound)
• Willing and able to participate; provides written informed consent
• Owns a mobile phone capable of step-count data collection

Exclusion criteria

• Multiple pregnancy
• History of miscarriage in previous pregnancies
• Chronic systemic disease (e.g., diabetes, hypertension, thyroid disease)
• Detection of fetal anomalies
• Drug or substance abuse
• Current cigarette smoking
• Serious psychiatric illness