Balance

Evidence from several studies revealed that pregnancy is also likely to afect balance abili-ty (Butler et al., 2006; Cakmak et al., 2014; Inanir et al., 2014; Jang et al., 2008). While changes in postural stability seem to be small and physiologically irrelevant in the EP (Butler et al., 2006; Inanir et al., 2014), substantial impairments have been detected in T2 and T3 (Inanir et al., 2014; Jang et al., 2008; Butler et al., 2006; Nagai et al., 2009;

Ribas and Guirro, 2007).

Several studies analyzed postural stability in pregnant women in static conditions as-sessing CoP movements during motionless standing on a force plate (Butler et al., 2006;

Jang et al., 2008; Nagai et al., 2009; Opala-Berdzik et al., 2014, 2015; Oliveira et al., 2009).

The fndings from these studies are inconsistent and difer greatly depending on the ana-lyzed parameters. While Nagai et al. (2009) reported a larger A-P sway path in pregnant women in the 30^th WoP compared to non-pregnant women, another research group did not establish any diferences in this sway parameter between the advanced stage of pregnancy

and PP (Opala-Berdzik et al., 2014). Butler et al. (2006) described a signifcant larger sway velocity in T2 and T3 compared to non-pregnant women. In contrast, other authors did not detect any diferences between a pregnant and non-pregnant group (Jang et al., 2008) or the same women during and after pregnancy (Opala-Berdzik et al., 2014).

Inanir et al. (2014) conducted dynamic measures in pregnant and non-pregnant women during bipedal standing using a Biodex Balance System with an inclinable platform (see chapter 4.2). The results of the overall balance ability scores demonstrated a signifcant decline in dynamic stability in T3. Another research group using the same measurement device, however, did not observe any changes in the balance scores (Cakmak et al., 2014).

The latter fndings are likely to refect observations by McCrory et al. (2010b) assessing A-P sway in response to translational perturbations during bipedal standing on a mo-vable force plate in 41 pregnant and 40 non-pregnant women. The A-P sway in pregnant women was not signifcantly diferent from the non-pregnant women. There were also no diferences between the groups for diferent perturbation amplitudes (small, medium and large) or perturbation directions (forward and backward) (McCrory et al., 2010b).

While studies consistently report balance changes for the sagittal plane (Jang et al., 2008; Nagai et al., 2009; Ribas and Guirro, 2007; Opala-Berdzik et al., 2015), the coronal plane has been described to require further research (Branco et al., 2014). Jang et al.

(2008), however, state that the coronal plane seems likely to be less afected by pregnancy as impairments can more easily be compensated by a wider stance width (Jang et al., 2008; Opala-Berdzik et al., 2015; Lymbery and Gilleard, 2005; Oliveira et al., 2009). A similar compensatory mechanism for the sagittal plane has not yet been established.

Further research on pregnant women focuses on the efect of visual input on postural stability (Oliveira et al., 2009; Nagai et al., 2009; Butler et al., 2006; Opala-Berdzik et al., 2015). In a study by Oliveira et al. (2009), 20 pregnant women were instructed to stand on a force plate as motionless as possible with their eyes opened and closed. The sway area signifcantly increased in T2 and T3 for the eyes closed condition. These fndings indicate that women in the advanced stage of pregnancy rely more heavily on visual cues for balance control (Oliveira et al., 2009). Similar results have been observed by

Opala-Berdzik et al. (2015) who also report an increase in the A-P sway path and velocity in the eyes closed condition from the EP to LP.

In contrast, Nagai et al. (2009) suggest that reliance on visual cues during pregnancy is less important than reliance on somatosensory input. The authors analyzed M-L postural sway data from pregnant and non-pregnant women. Irrespective of whether eyes were open or closed, the power spectrum of the pregnant group demonstrated reduced frequencies larger than 1 Hz. As frequencies larger than 1 Hz are generally stabilized by somatosensory input, the results indicate that for balance maintenance during pregnancy, women receive input from somatosensory sources more intensively than non-pregnant women.

It remains debatable whether postural stability remains diminished in the PP. Opala-Berdzik et al. (2015) detected a signifcant improvement in postural sway two months postpartum. In contrast, Butler et al. (2006) reported a signifcant impairment in postu-ral sway six to eight weeks postpartum (Butler et al., 2006). Jang et al. (2008) found that impairments in M-L postural sway remain even six months after childbirth.

In conclusion, there is evidence to suggest that pregnancy leads to impairments in static and dynamic postural stability in the advanced stages of pregnancy (Butler et al., 2006;

Cakmak et al., 2014; Inanir et al., 2014; Jang et al., 2008). The fndings from the studies, however, are inconsistent and difer depending on the analyzed balance parameters (Na-gai et al., 2009; Opala-Berdzik et al., 2014; Butler et al., 2006). Impairments in postural stability have been found to primarily occur in the sagittal plane (Jang et al., 2008; Nagai et al., 2009; Ribas and Guirro, 2007; Opala-Berdzik et al., 2015). The coronal plane is less likely to be afected as an increased stance width may compensate for instability in the lateral direction (Jang et al., 2008). Balance control in the advanced stages of pregnancy is associated with an increased reliance on visual cues (Oliveira et al., 2009; Nagai et al., 2009; Butler et al., 2006; Opala-Berdzik et al., 2015). However, another study found that pregnant women rely more heavily on somatosensory input in this time period (Nagai et al., 2009). There is disagreement about whether a decline in balance performance du-ring pregnancy is accompanied by long-term efects in the PP (Opala-Berdzik et al., 2015;

Butler et al., 2006; Jang et al., 2008).