Characteristics of the control of standing posture during pregnancy

During pregnancy, the physical and mental states greatly change. We investigated the influences of pregnancy and anxiety on postural control in pregnant women (P) standing upright in the late trimester. An analysis of posturograms revealed that the area of body sway and length of antero-posterior body sway were greater in P than those in non-pregnant controls (NP). No difference was found in the medio-lateral body sway between P and NP. Fast Fourier transform analysis of body sway showed that the percentile power of the 1.0-10.0Hz band in the medio-lateral axis was smaller in P than in NP irrespective of whether the eyes were open or closed. P were divided into a high (HA) and low (LA) anxiety group on the basis of state anxiety scored by Spielberger's State- and Trait-Anxiety Inventory. A positive correlation was identified between state anxiety and the area of body sway in HA standing with eyes open. This correlation was diminished when the eyes were closed. Body sway of over 1Hz is generally stabilized by somatosensory input, therefore, the results show that body sway in the medio-lateral axis is stabilized in P by increasing the sensitivity to somatosensory cues. High anxiety during pregnancy destabilizes the standing posture when the eyes are open. The correlation between anxiety and body sway revealed by our previous studies in college students was also confirmed in P, suggesting that humans with high anxiety abstract visual cues differently from those with low anxiety.