Full length articleUpright balance control strategies during pregnancy
Introduction
Pregnancy is recognized as a period of inherent morphological and physiological changes resulting in modifications of the inertial properties of the body segments and increasing postural instability [1]. Weight gain, abdominal growth, increased circulating relaxin, stretched abdominal muscles, and increased amount of interstitial fluid in the extremities affecting sensory input are some of the numerous contributing factors to this process [2,3]. One in four pregnant women experience a fall event and more than 50% of these falls will result in injuries [4]. This falling rate is alarming when linked to approximately 6.3 million pregnancies per year in the US [5]. Despite these large numbers, relatively little effort has been directed to the study of mechanisms leading to increased fall risk during pregnancy. It is important to investigate pregnancy-related changes in postural control to better develop efficient programs for fall prevention and balance training programs in order to reduce fall risk in this population.
Since modifications in the pregnant body emerge in a relative short period of time (40 weeks) and affect body segments differently; they are likely to induce the Central Nervous System to adjust its motor outputs in order to achieve optimal joint control during upright balance [9]. Currently, it is not clear whether CNS adaptations occur during pregnancy or how they are implemented. However, it is expected that the absence of optimal postural control will likely increase the risk of falling during pregnancy as well as its inherent comorbidities (e.g. fractures, fetus trauma, placenta abruption) and rates of maternal and fetal mortality [6].
The common paradigm used to investigate postural behavior of pregnant women is the analysis of body sway characteristics (e.g. amplitude, variability, and signal structure) extracted from recordings of the body’s center of pressure (COP) during the execution of upright stance [[7], [8], [9]]. This paradigm is constructed upon the rationale that posture control is a multi-faceted process that is largely dependent on the recognition of the state and mechanical features of body segments and the consequent harmonic integration of neurophysiological processes occurring in multiple areas of the Central Nervous System [10]. Therefore, even subtle changes in these processes will likely result in modifications of postural behavior that can be recognized for clinical purposes [11,12]. Studies regarding postural behavior of pregnant women have rendered important but contradictory results. For example, Nagai et al. [7] reported significant changes in body sway indices in late stages of pregnancy (30th week) including larger magnitude of sway and structural changes in the power density function of recordings of the COP coordinates in medial-lateral direction. Oliveira et al. [8] reported earlier changes in the power density function and in both anterior-posterior and medial-lateral directions of postural sway and suggest their dependency on several other factors including the availability of visual input and size of the base of support. Despite these studies suggesting the occurrence of postural sway behavior changes during pregnancy, a recent report by Opala-Berdzik et al. [9] have contradicted these findings by showing no changes in postural behavior characteristics during pregnancy.
It is likely that discrepancies found in previous studies may be partly related to the methodology employed and postural indices used to measure body sway. Gao et al. [13] have shown that trial duration has a significant impact to the analysis of postural behavior in bipedal stance and longer recording times are needed to allow the development of certain postural behaviors. In addition, recent reports suggest the inclusion of multiple indices of postural sway to facilitate the establishment of clearer patterns of postural behavior exhibited in a cohort of participants [11,12,14].
In this study, we aimed to bridge some of the gaps mentioned by focusing on the analysis of multiple metrics associated with body sway characteristics in women representing the three trimesters of pregnancy and non-pregnant controls. Here, we apply contemporary procedures of recording and analytical methods to increase our ability to detect changes in postural behavior. In particular, we utilize measures of sample entropy to study the structure of the COP signals and potential modification in mechanisms of postural control. Our hypothesis is centered on the prediction that body oscillation patterns will in fact be modified during pregnancy. We hypothesized that with increase of time post-conception there will be significant increase in the amplitude of body sway, regularity of body sway in time, and anterior pelvic tilt through the three trimesters of pregnancy. We expect the results from this study will aid further development of a comprehensive panel of metrics to be used clinically in screening pregnant patients under higher risks of falling and elaborating efficient balance training for this population.
Section snippets
Participants
Forty volunteer women participated in this study and formed four groups:
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Non-pregnant group (NP). Control group formed by ten non-pregnant women with no previous history of pregnancy. Other inclusion criteria were: absence of systemic, vestibular, neurological, or musculoskeletal disorder; no history of fractures or surgery of the lower extremities or spine, degenerative joint disease, or amputations.
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Pregnancy groups (P1, P2, and P3). Three groups of ten pregnant women each representing the
Effect of pregnancy on anthropometric characteristics and pelvic inclination
Table 1 shows age and anthropometric characteristics recorded across participants for each group studied. As expected, Kruskal-Wallis statistical results showed an effect of pregnancy on body weight and body mass index. Mann-Whitney U post-hoc tests revealed significant changes in body weight for P2 and P3 when compared to NP (p=0.034 and p=0.020, respectively) while BMI was found to be significantly larger for P1, P2, and P3 also when compared to NP (p = 0.017, p = 0.001, and p = 0.001;
Discussion
The current study was designed to investigate how pregnancy affects postural control in each trimester of pregnancy by analyzing pelvic inclination and body sway behavior using posturography. In general, pregnant women seem to present a larger body sway accompanied by a more regular medial-lateral pattern of oscillation and a more synchronized anterior-posterior and medial-lateral sway already at their first trimester. We observed a significant increase in anterior pelvic tilt starting on the
Disclosure statement
The authors report no conflict of interest and up to this date this research has not been presented in any format.
Financial support for research
None.
Acknowledgement
The authors would like to thank all participants.
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Comparison of static postural sway characteristics between pregnant and non-pregnant women
2023, Journal of BiomechanicsCenter of pressure characteristics differ during single leg stance throughout pregnancy and compared to nulligravida individuals
2022, Gait and PostureCitation Excerpt :Pregnant participants presented with smaller sway and mean velocity during the second and third trimesters, greater median frequency during the third trimester and post-partum, smaller SampEn AP during the second and third trimesters, and smaller SampEn ML during the second trimester. The results of the current study are contrary to the greater sway and greater sway velocity observed during double limb stance previously [6,10,11], but are consistent with the smaller sway observed previously in pregnant females during perturbations and particularly in pregnant females who experienced a fall during pregnancy [12–14]. Often lower numbers for sway and sway velocity are thought to reflect greater stability (less amplitude and rapid change in the center of pressure position)[6].
Motor control of the spine in pregnancy-related lumbopelvic pain: A systematic review
2022, Clinical BiomechanicsCitation Excerpt :One reason explaining these large discrepancies could be the gestational age at the time of the experiment that was different between studies. Physiological (Mens et al., 2009), hormonal (Mantle et al., 2019), anatomical (Mantle et al., 2019), postural (Danna-Dos-Santos et al., 2018) and biomechanical (Conder et al., 2019) changes progress during pregnancy and may have influenced motor control adaptation to pain during gait. Also, the large number of variables studied in these studies that may have increased type I errors.
Changes in static balance during pregnancy and postpartum: A systematic review
2022, Gait and PostureCitation Excerpt :Seven studies (54%) used a sampling frequency of 100 Hz [23,25,36–40], while only one (8%) used a cut-off frequency of 10 Hz [23]. Five studies (38%) recorded COP during at least three trials [22,25,36,37,40], and one study (8%) used a sampling duration of at least 90 s [23]. About half of the studies (54%) reported the instructions, i.e. “to stand quietly or motionless”, or “to maintain a stationary standing position” [24,36,38–42].
Assessment of postural sway with a pendant-mounted wearable sensor
2022, Gait and PostureInfluence of type 1 diabetes on the postural control of women in the third gestational trimester
2020, Clinical BiomechanicsCitation Excerpt :There is an accentuation of lumbar lordosis with anterior rotation of the pelvis to stay in the upright position, with the center of pressure positioned on the support base (Elsayed et al., 2017; Schröder et al., 2016). A study (Danna-Dos-Santos et al., 2018) showed a significant increase in anterior pelvic tilt from the second trimester and was even higher in the third trimester. The developing fetal load increases the demand of the lumbar spine, inducing increased lumbar lordosis and anterior pelvic tilt (Robinson et al., 2010).