Immediate effect of abdominal muscle contraction on pelvic floor morphology in postpartum women

Objective This study aimed to explore the immediate effect of abdominal muscle contraction on the pelvic floor morphology in postpartum women. Methods This observational cross-sectional repeated-measures study recruited 90 participants who visited the Fujian Maternity and Child Health Hospital from May 2024 to March 2026. All participants underwent pelvic floor assessments using four-dimensional (4D) ultrasound in seven different positions. Results The results showed a general decreasing trend in the hiatal area and retrovesical angle and an increasing trend in the urethral tilt angle during pelvic floor muscle contraction. The bladder neck position, cervical position, and rectal ampulla position descended during drawing-in ( Padj = 0.005, Padj = 0.106, and Padj = 0.018, respectively), head-lift1 ( Padj = 0.002, Padj = 0.032, and Padj 0.001, respectively), head-lift2 ( Padj 0.001, Padj 0.001, and Padj 0.001, respectively), and 90 °flexion of the hips and knees ( Padj 0.001, Padj = 0.055, and Padj = 0.495, respectively). The differences remained significant for pelvic floor muscle contractions during the drawing-in, head-lift1, head-lift2, and one-leg lift for bladder neck positions ( Padj 0.001, Padj = 0.014, Padj = 0.023, and Padj = 0.033, respectively) and head-lift2 for the rectal ampulla position ( Padj 0.001). In contrast, the cervical position were higher than rest during pelvic floor muscle contractions in drawing-in ( Padj 0.001), head-lift1 ( Padj = 0.011), one-leg lift ( Padj 0.001), and 90° flexion of the hips and knees ( Padj = 0.006). Conclusion Drawing-in, head-lift, and flexion of the hips and knees were associated with immediate pelvic organ descent and hiatal area enlargement in this study, with the head-lift2 maneuver showing a relatively higher mechanical loading degree. The simultaneous contraction of the pelvic floor muscles during these maneuvers correlated with an immediate reduction in pelvic organ descent.