Magnetic resonance imaging evaluation of pelvic floor structure during pregnancy

Among the various risk factors of pelvic floor disorders, pregnancy has been reported to affect the pelvic floor structure; however, not all these effects have been understood yet. The aim of this study is to elucidate how pregnancy affects pelvic floor structure via magnetic resonance imaging (MRI).We conducted a retrospective study between January 2010 and December 2019 to extract clinical records of pregnant and non-pregnant women, who underwent MRI for obstetrical diseases and ovarian benign tumors, respectively. The data on age, body mass index (BMI), complications, gravida, parity, gestational age, and obstetrical history were collected, and pubo-coccygeal line (PCL), pubo-rectal line (PRL), and M line (ML) on their MR images were measured. Statistical analyses were performed with Wilcoxon test, chi-square test, and Kruskal-Wallis test with Steel-Dwass post hoc test as appropriate. Statistical significance was set at P 0.05.We analyzed the reports of 56 (pregnancy group) and 106 women (non-pregnancy group). There was no significant difference in age or BMI, while the obstetric history was significantly different between these groups. Median PCL, PRL, and ML in the pregnancy group were significantly longer than those in the non-pregnancy group (114.1 mm vs. 110.0 mm, P = 0.018; 48.6 mm vs. 41.6 mm, P0.0001 and 21.7 mm vs. 10.0 mm, p0.0001. respectively). The subgroup analysis of the effect of pregnancy and vaginal delivery (VD) history on changes in these lines revealed that pregnancy-induced PRL increase tended to recover to the reference level of "non-pregnant without VD," but ML increase did not fully recover.MRI revealed a strong effect of pregnancy on pelvic floor structure.