Age, parity, and prolapse: interaction and influence on levator bowl volume

The objective was to test the hypotheses that a linear relationship exists between age and levator bowl volume (LBV); and that age, parity, and prolapse are independently associated with LBV.

We conducted a secondary analysis of data from nulliparous women, parous controls, and prolapse (Pelvic Organ Prolapse Quantification (POP-Q) Ba ≥ 1 cm) cases from each of three age groups: young (≤40), mid-age (50-60), and older (≥70). LBV was measured using MRI at rest and Valsalva as the 3D space contained above the levator ani muscles and below the sacrococcygeal junction-to-inferior pubic point reference plane. Linear regression models were used to examine the effects of age, parity, prolapse, and their interactions (age*parity and age*prolapse) on LBV.

Each group consisted of 9-12 women. LBV_Rest increased with age in a nonlinear fashion. For nulliparous women, the median value increased 4.7% per decade from the young to mid-age group and 84% per decade from the mid-age to older group; for parous controls, the corresponding increases were 38% and -0.5%; and for women with prolapse, they were 46% and 11%. Age and prolapse status (both p<0.001) were found to be significant independent predictors of LBV_Rest. Interactions between age*prolapse (p=0.003) and age*parity (p=0.045) were also independently associated with LBV_Rest.

Parity and prolapse influence how age affects LBV_Rest. In nulliparous women, age had little effect on LBV_Rest until after mid-age. For women with prolapse, LBV_Rest increased at a much earlier age, with the biggest difference occurring between young and mid-age women.