Elsevier

Gait & Posture

Volume 66, October 2018, Pages 7-12
Gait & Posture

Full length article
Upright balance control strategies during pregnancy

https://doi.org/10.1016/j.gaitpost.2018.08.004Get rights and content

Highlights

  • Study focused on investigating how pregnancy affects postural control.

  • The first trimester of pregnancy showed significantly larger body sway.

  • At third trimester the center of pressure migrated posteriorly.

Abstract

Background

Morphological and physiological changes during pregnancy are considered to interfere with the mechanisms of postural control and potentially increase the risk of falling. A clear understanding of these mechanisms is important to improve pre-natal care and reduce the fall risk in this population.

Objectives

This study focused on investigating how pregnancy affects postural control in each trimester of pregnancy by analyzing pelvic inclination and body sway behavior. Our main hypothesis was that balance control and posture would change during pregnancy. More specifically, pregnancy would increase sway amplitude, anterior pelvic tilt, and body sway regularity in time.

Study design

Forty women formed four groups: non-pregnant women (NP) and women at their first, second, and third trimester of pregnancy (P1, P2, and P3, respectively). All participants performed (1) postural evaluation of the pelvic inclination using a digital system of postural analysis and (2) instrumented posturography using a force platform to collect the coordinates of the body’s center of pressure (COP) during quiet bipedal stance for 120 s. Kruskal-Wallis H test and post-hoc Mann-Whitney U tests were used to investigate the effects of pregnancy (NP, P1, P2, and P3) on pelvic inclination angle and postural indices computed from the COP signals.

Results

Results revealed significant 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 the first trimester of pregnancy. The averaged COP migrated posteriorly at third trimester of pregnancy and the anterior pelvic tilt increased at second and third trimesters.

Conclusions

Our results indicate the existence of changes in posture and balance metrics even at early stages of pregnancy. We suggest the use of posturography as one of screening tools for postural instability and fall risk 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:

  • -

    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.

  • -

    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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