Asymmetry in Paraspinal Muscles as a Predictor of the Development of Pregnancy-Related Low Back and Pelvic Pain: A Prospective Study.

Abstract Background: The etiology of pregnancy-associated lumbopelvic pain (LPP) is not clear at present. This condition is highly heterogeneous with different development and subtypes, including low back pain (LBP) and pelvic girdle pain (PGP). Paraspinal muscles are of importance to maintain the spine's functional stability, and their weakness participates in the occurrence of LPP. Therefore, this study aims to determine the asymmetry in the paraspinal muscle before pregnancy and evaluating its association with pregnancy-associated LPP.Methods: This was a prospective case-control study conducted from January 2017 and December 2018. 171 subjects (mean age ± SD, 27.4±5.8 years) were finally divided into the LBP group, PGP group, and no LPP group. The mean value of F-CSA's ratio to T-CSA (F/T CSA) was used to determine whether the bilateral paraspinal muscle was asymmetrical. Total muscle CSA (T-CSA), functional CSA (F-CSA), and F/T CSA were measured unilaterally and compared between groups. Logistic regression was performed to determine the risk factors for pregnancy-associated LPP. The Pearson correlation coefficient was performed to test the relationship between asymmetry in F/T-CSA and pain rating.Results: 124 subjects (72.5%) (28.5±5.2 years) had the LPP during the pregnancy. 48 (38.7%) individuals had LBP, and 76 (61.3%) had PGP. A total of 39 (31.5%) women unrecovered from LPP. F/T-CSA was significantly decreased in LBP than those in the PGP group and control group (0.03±0.02 vs. 0.05±0.03 vs. 0.12±0.05, P <0.001). Meanwhile, significant differences were detected in any two groups (all P <0.001). Asymmetry in the paraspinal muscle (adjusted OR=1.5), LBP (adjusted OR=1.6), LPP in a previous pregnancy (adjusted OR=1.4), sick leave≥90 days (adjusted OR=1.2), and heavy labor (adjusted OR=1.2) were risk factors for the unrecovered LPP during pregnancy.Conclusions: Asymmetrical muscular compositions could lead to abnormal biomechanics for the segmental motions. One-lateral-directed physical training and stretching may help decrease the occurrence and severity of this condition.