This study demonstrates that pregnant supports assist immediate hemodynamic adjustments during postural changes. It is believed that the elasticity of pregnant supports offer some additional function of baroreceptors in healthy pregnancies in the standing position. As the hydrostatic pressure diminishes during the side lying position, it will lower hemodynamic adjustments with greater immediate blood perfusion With limitation during the last trimester, these compensations cannot be demonstrated in the supine position due to the risk of abdominal aorta compression [20]. Daily physical activity and routine pregnant exercises do not affect hemodynamics. From our results, pregnant supports are recommended with no limitation on lower limb hemodynamics.
The physiologic adjustments in pregnancy to meet the metabolic demands for both mother and fetus are critical, particularly during postural changes and daily physical activities. On the other hand, hemodynamic insufficiency during pregnancy leads to complications of pregnant women in North America [21]. Several cardiovascular adjustments in pregnant women necessarily compensate to lower the above risks during pregnancy [22].
The current study aimed to report anthropometric status during the last trimester and will not focus on the dynamic gestational weight gain (GWG). Previous investigations on anthropometry of pregnant women reported wide ranges of BMI from 18–20 kg/m2 in South Asia [23] and 25.3 up to 68.3 kg/m2 among the South-Asian pregnant women [24]. With report in South-East Asia, maternal BMI in this study is categorized as the borderline of pregnant obese group [25]. Total body water of 50% [26] and daily basal metabolic rate of 1300–1400 Kcal are accepted [27]. The dynamic changes in body composition from fluid shifting between mother and the growing fetus may be a major explanation on pregnant anthropometric changes [28]. Other body composition variations during gestation depends on methods being used and will not able to differentiate between mother and fetus [29]. Thus, this study will pay attention on hemodynamics changes.
To our knowledge, this is the first study on hemodynamics in pregnant women during postural changes and physical activities. For safety reasons, invasive methods have rarely been done in pregnant subjects [30], thus, most previous investigations used non-invasive methods of echocardiogram and magnetic resonance images, which are limited by the mother being set in a steady position [31, 32]. To overcome the above limitation, the present study used non-invasive method of impedance cardiographs (Physioflow®), which shows high validity and reliability and permits continuous measurement in pregnant women during postural changes [33, 34].
Pregnancy is associated with various physiologic adaptations to ensure adequate uteroplacental circulation for fetal growth and development [35]. Those hemodynamic compensations involve factors of either inside or outside the heart. Cardiac output increases throughout early pregnancy, and peaks in the last trimester, usually to 30–40% above baseline. The rise in cardiac output is mediated to estrogen-induced higher overall blood volume, which in turn increases pre-load and stroke volume [22]. A long-term study throughout the period of pregnancy by imaging found that there were fluctuations of SBP and DBP from thickening of intima-media (IM) and inter-adventitial diameter (IAD) of the common carotid artery (CCA) on the first trimester which returned to pre-pregnancy level on the last trimester [36]. The absolute outcome of vasodilation during pregnancy is known as systemic compensation, which shows the remarkable drop in systemic vascular resistance (SVR, 900 dynes.sec− 1.cm− 5) during the second trimester and the gradual increase to near pre-pregnancy levels (1200 dynes.sec− 1.cm− 5) during the last trimester [22]. Another reason for the reduction in SVR is due to smooth muscle relaxation and overall vasodilation caused by elevated progesterone and relaxin, leading to a fall in blood pressure [37]. Diastolic blood pressure consistently decreases between 12–26 weeks, and increases again to pre-pregnancy levels about 2 weeks after delivery [22]. This is due to increased vascular compliance shown during the first trimester [38]. As a result of vasodilation, the reductions of SBP, and DBP are seen in this study. In fact, these blood pressures fall since early pregnancy with the lowest at the second trimester, about 5–10 mmHg below baseline [22]. No matter which pregnant support is being used, our study shows that reductions of SBP, DBP, and HR are particularly seen in the side lying position. These occur at the 1st and sustain to the end of the 3rd minute. This adjustment is possibly via the increase in maternal sensitivity of baroreceptors [39]. Considering the cardiac contractility during physical activity, this study found no changes in SV, end diastolic volume (EDV), and EF among different supports. This is similar to evidence from previous study in that there is no change in cardiac contractility, left and right ventricular ejection fractions during pregnancy [31].
It is believed that the size of growing fetus will further put more discomfort on the mother’s pelvic organs including decreased gastrointestinal motility, prolonged transit time, and displacement of the intestines upward and outward [40]. The risks of pelvic blood vessel compression are likely aggravated by the growing fetus, which is particularly prohibited in the supine position [20]. Thus, investigation in the lateral side lying position is a standard practice for clinical maternity care provider [41]. It is speculated that exercise intolerance might possibly appear in pregnant women. However, we did not find any difficulties during exercises and daily physical activities. Possibly, the intensity of the two modes of physical stress used in this study were too low.
Questionnaires used in the present study were aimed to qualitatively estimate the feeling and perception of pregnant women while using different supports during physical activities. For ease of use, investigators simply modified a 5-point scale questionnaire [18, 19]. For safety reasons, some select exercises were chosen for pregnant women as previously prescribed [17]. This study found satisfaction index (CW) above 3.6 out of 5. PB and PP supports. Pregnant supports in this study had been partly designed based on the Three-Point Pressure Principle [42]. With a semi-rigid portion (A band, Fig. 1) where lines of force from elastic bands point directly toward the A band. This design will prevent forward displacement of abdominal contents, as well as hyperextension of the lumbar spinal column [43]. Comfort feeling during movement is also evaluated during pregnancy according to a previous study [44]. Comfortable perception in pregnant women would be helpful for the design of maternity support that required to satisfy ergonomic needs with pain-free feeling. In our study, it seems likely that PB support is the most preferential. This finding is consistent with a recent study showing that maternity support garments are regarded as a convenient and safe device to stabilize the lumbar spine so as to relieve pain [45]. In addition, Ho and co-workers reported that maternity support garments are a convenient and easily-accessible therapy to manage lower back pain during pregnancy and are frequently recommended and worn by pregnant women [46].