Posture Changes During Pregnancy: Influence of Footwear on the Risk of Falling of Pregnant Women

During pregnancy, the female body undergoes tremendous physical, physiological, and hormonal changes. The average woman gains between 25 and 35 pounds throughout pregnancy. 1 This sudden and localized increase in weight shifts her center of mass forward, changing her posture and decreases her postural stability. Because the risk of falling increases during pregnancy and although non-strenuous activity favors positive pregnancy outcomes 3 , pregnant women are often instructed to avoid physical activities. Because there is no strategy to mitigate this increase in the risk of falling, 27 percent of women fell at least once during pregnancy and these falls account for 17 to 39 percent of all traumatic injuries to pregnant women. 2 These falls also lead to a large financial burden on the health care system and take an emotional toll on society. 4 This study aims at measuring the influence of footwear on the risk of falling of women throughout a simulated pregnancy. Starting from anthropomorphic data, we developed a model of the female body during pregnancy, correlating changes in weight and volume. The model is validated on independent measurements on pregnant women. 5 The Body Mass Index (BMI) of a woman increases in average by 5.3 during pregnancy. 1 For a subject with known initial BMI, the model predicts the value and location of the weight gain. Hence, the model is a subject-specific predictor of weight changes per body segment during pregnancy. We quantified the risk of falling while standing and during gait. We recruited 16 healthy females (18-30 years old, BMI < 26, 10 subjects for standing and 6 subjects for gait) to participate in our study approved by the IRB at OSU. Each subject participated in 4 different testing sessions (not pregnant and beginnings of the 1 st , 2 nd , and 3 rd trimesters). The pregnancy was simulated by adding specific weights to their upper and lower trunk, bottom, thighs, and lower legs, according to the model prediction, using an empathy belly and strap on weights. During each session, the subjects stood or walked on a pressure mat during 5 minutes for each of the following footwear conditions: barefoot, flats, sport shoes, heels, sport shoes with ankle braces, and heels with ankle braces. For each condition, we measured the pressure under the feet. From the recorded data, we determined the position and velocity of the Center of Pressure (CoP) through time, the base of support (area encompassing both feet), the sway, and the average step width and length. Results for the standing study show that the average distance to boundary of the CoP decreases in the mediolateral direction and stays constant or increases in the anteroposterior direction. This indicates the postural stability remains constant in the anteroposterior direction but decreases in the mediolateral direction during pregnancy. Flats and barefoot conditions tend to lower the risk of falling, while heels and heels with brace tend to increase the risk of falling. Preliminary results for the gait study show that the sway varies with the footwear condition. The sway seems to increase with heels with braces, while it either decreases or stays constant with flats and sports with braces. The average step width increases for all footwear conditions during pregnancy, while the averaged step length seems to vary with footwear conditions.