Alterations in the anterior limit of stability during pregnancy and postpartum under visual deprivation

Introduction: Pregnancy is associated with anatomical and physiological adaptations that may affect postural control (Jang et al., 2008; McCrory et al., 2010; Nagai et al., 2009). Although balance disturbances during pregnancy have been widely investigated, evidence regarding changes in anterior limit of stability (LoS) throughout pregnancy and the postpartum period remains limited and inconsistent (Bey et al., 2018; Sancar et al., 2021; Takeda et al., 2018). Therefore, this study aimed to compare anterior LoS in healthy women at different stages of pregnancy and during the postpartum period and to determine the influence of visual deprivation on LoS performance.Methods: Thirty healthy women (mean age 28.2 ± 3.7 years) were assessed during early pregnancy (≤ 16 weeks of gestation), late pregnancy (approx. 3 weeks before the expected due date) and at two and six months postpartum. Anterior LoS was evaluated using a force plate under both eyes-open and eyes-closed conditions. One 30-s trial was recorded for each visual condition at each session and was divided into: phase 1 - quiet standing (10 s); phase 2 - a pendulum-like transition from quiet standing to maximal forward leaning (approx. 3 s); and phase 3 - maintenance of the maximal forward-leaning position (approx. 17 s). The analyzed center of pressure variables included postural adjustment (PA) and maximal forward lean (MFL) during phase 2, and stable forward lean (SFL), root mean square (RMS), mean velocity (MV), and mean frequency (MF) during phase 3. Body weight and stance width was also measured at each assessment session.Results: Repeated-measures ANOVA revealed a significant main effect of Vision on all evaluated variables, with the eyes-closed condition resulting in greater PA, RMS, MV, and MF, but lower MFL and SFL compared with the eyes-open condition. Significant main effects of Session were observed for MFL, SFL, MV, and MF. However, after adjustment for multiple comparisons, significant session-related differences were found only MFL and SFL, which increased from two to six months postpartum, and for MF, which decreased from early to late pregnancy. No significant Vision × Session interactions were observed for any of the evaluated LoS variables.Conclusions: Anterior LoS remained stable throughout pregnancy and the postpartum period. Nevertheless, LoS assessment across visual conditions revealed changes in postural control, including increased forward lean during the postpartum period and reduced sway frequency with advancing pregnancy. The increase in forward lean during the postpartum period suggests that recovery of functional stability continues beyond the first two months after childbirth, whereas the lower sway frequency in late pregnancy may reflect the adoption of a slower and more conservative postural control strategy in response to pregnancy-related biomechanical changes.Acknowledgements: We would like to acknowledge the late Prof. Andrzej Markiewicz for his contributions to the development of the project and for securing the initial funding (grant no. 2 P05D 052 27, Polish Ministry of Science and Higher Education). We also acknowledge the support of the Scientific Grant Agency of the Slovak Academy of Sciences (VEGA 2/0098/25).