Pessary treatment is a popular option for women with pelvic organ prolapse; however, success rates are limited, mostly due to dislodgement of the pessary. In literature, several support mechanisms are proposed such as support by the levator ani muscle and the uterus which acts as a lever to keep the pessary in place. To improve success rates of pessary therapy, the support mechanism should be further investigated.

The aim of this study is to identify ring-shaped pessary support mechanisms by comparing upright magnetic resonance imaging data of successful and unsuccessful pessary users.

Upright magnetic resonance scans were performed after obtaining informed consent in patients with and without pessary in 30 successful and 29 unsuccessful cases. The study was approved by the medical ethics committee. We analyzed the position of the pessary with respect to the levator ani muscle, the pubic symphysis, and the uterus. For comparison of the levator ani muscle position with respect to the pessary, principal component analysis was used. Statistical analyses were performed using SPSS version 29.0.1.0 (SPSS, Chicago, IL). Differences between the groups were analyzed using a 2-sided t -test or Mann-Whitney U test where appropriate for the continuous data. For the categorical data, a chi-square test was performed.

The pessary is significantly lower in the pelvis in the unsuccessful group (median 1.9 cm below the Pelvic Inclination Correction System (PICS) line [range, −0.9; 4.0]) than in the successful group (median 0.6 cm below the PICS line [range, −1.8; 2.6]). The angles of the pessary with respect to the PICS line, and the distances of bladder and uterus to the PICS line, showed no significant difference between groups.

The first principal component of the levator ani muscle shows a significantly lower position of the pessary in the levator ani muscle for the unsuccessful group ( P < .001) and accounted for 64.8% of shape variation.

With regards to the uterus position, in the successful group, the cervix is in the center of the pessary, with the proximal edge of the pessary positioned in the posterior fornix. While in the unsuccessful group, the cervix is located near the proximal edge of the pessary. Additionally, the unsuccessful group had 7 women with a hysterectomy, compared to none in the successful group, although this was not part of the inclusion/exclusion criteria.

These findings support the hypothesis that the pessary is kept in place by the levator ani muscle and the uterus lever mechanism. Knowledge on these support mechanisms can guide development of new pessary shapes or even personalized pessaries for unsuccessful users.