A 27% fall rate is estimated in pregnant women (Dunning.,2010) which accounts for more than 50% of the reported injuries in this population (Dunning et al.,2003). Serious maternal comorbidities include contusions, fractures, sprains, placental abruption, preterm labor, and miscarriages, and fetal comorbidities include fetal distress, fetal hypoxia, and fetal death (Mirza et al.,2010).

Pregnant women may fall due to physical, physiological, and biomechanical changes that occur during pregnancy, which reduces postural balance with the advance of gestation (Opala-Berdzik et al.,2014). These changes include an increase in maternal weight, alterations in the center of gravity with varying skeletal alignment, and increased joint and ligament laxity (Cakmak et al., 2014, Ramachandra et al., 2015) which may affect the ankle proprioception among pregnant women leading to imbalance (Ramachandra et al.,2015; Ramachandra et al.,2011). With the advancement of pregnancy, a greater rate of change in weight is reported in the lower trunk compared to other body segments. Increased size of the uterus with fetal weight gain accounts for the 30% increase in abdominal mass from the second trimester of pregnancy (Jensen et al.,1996). This increased abdominal morphology has been linked to reduced static stability and compensatory spinal alignment to ensure postural balance in pregnant women (Opala-Berdzik et al.,2015).

Computerized static posturography is a quantitative method for assessing upright balance function under a variety of tasks that effectively simulate conditions encountered in daily life (Roceanu et al.,2014). In quiet standing, the Center of Pressure (CoP) is considered to reflect in part the motor mechanisms that ensure balance, precisely the maintenance of the projection of the Center of Mass (CoM) inside the base of support (Hof et al.,2005). The sway velocity measures provide a thorough assessment of postural control, particularly in terms of biomechanical and physiological characteristics, and the output of the posturographic measures can be readily interpreted (Błaszczyk et al.,2016). It is directly related to postural stability control and balance and has been used extensively in studies related to postural behavior in pregnant women (Roceanu at al.,2014; Błaszczyk et al., 2016, Jang et al., 2008). Postural control depends on the fine adjustments made in the body segments and its integration of neurophysiological processes occurring in multiple areas of the central nervous system (Oliveira et al.,2009).

Previous longitudinal studies which have compared postural sway between non-pregnant women and pregnant women across various trimesters have reported an increase in average radial displacement and larger anteroposterior displacement in pregnant women with no significant difference in mediolateral displacement between the groups. However, the sensory conditions tested only compromised visual input (Opala-Berdzik et al., 2015, Butler et al., 2006, Nagai et al., 2009). Other studies that investigated postural sway have tested in conditions where vision and base of support were compromised (Oliveira et al.,2009) or when visual and proprioceptive input was compromised (Souza et al.,2016). Existing studies that have compared the postural sway between pregnant and non-pregnant women have shown contradictory results and none of the studies have compared postural sway in sensory conditions such as uneven surfaces with narrow base conditions.

The foremost reported causes of falls at work for pregnant women include slippery floors, moving at a fast pace, and carrying an object or a child which occludes the vision (Roceanu et al.,2014). This indicates that pregnant women may lose their balance when the sensory input (vision, proprioception) (Roceanu et al., 2014, Ramachandra et al., 2015) or base of support is compromised. Therefore, the present study aimed to compare the postural sway characteristics between pregnant women in their third trimester and age-matched and body mass index-matched non-pregnant women under multiple sensory conditions where vision, proprioception, and base of support were compromised.