The increase in body mass and in the relaxin hormone level promotes adaptations of the musculoskeletal system in pregnant. These adaptations lead to biomechanical changes, in the lumbar spine and the lower limbs, and be responsible for low back pain during pregnancy. The purpose of this study was to investigate the prevalence of low back pain and if there is an association between biomechanical and postural factors and the occurrence of low back pain in pregnant. A repeated cross-sectional study was performed at the 25th, 30th and 35th pregnancy weeks. Biomechanical and postural factors were evaluated using computerized baropodometry and photogrammetry, a standardized questionnaire was used to assess socio-demographic and clinical variables. Initially, each independent variable, including potential confounders, was analyzed by univariate logistic regression. Subsequently, we employed a multiple logistic regression model. Variables with p â‰¤ 0.25 in the univariate analysis were entered in this model with low back pain as response variable. Altogether, 111 pregnant women were classified in two groups, with and without low back pain. Prevalence of low back pain was 60.36% (CI95% 51.05-69.14). Low back pain in previous pregnancies (OR = 6.14; CI95% 1.58-23.84); horizontal angle of the pelvis (OR = 1.3; CI95% 1.03-1.64) center of gravity asymmetry (OR = 1.08; CI95% 1.00-1.16); and parity (OR = 2.23; CI95% 1.03-4.82) were associated with low back pain in pregnants. According to our results low back pain is highly prevalent during pregnancy and it is associated with postural factors, low back pain in previous pregnancy and parity.