During pregnancy, the increase in body weight and uterine size leads to greater abdominal pressure, overloading the structures of the pelvic floor. During vaginal delivery, the musculature of the pelvic floor must be sufficiently elastic to stretch and allow the passage of the fetus. Spontaneous laceration or episiotomy can cause injuries to the muscle fibres, resulting in tissue damage that subsequently undergoes a physiological healing process, which may compromise elasticity and functionality. The most frequent dysfunctions of the pelvic floor in the postpartum period are urinary incontinence, pelvic organ prolapse and dyspareunia. Women who had vaginal birth are more prone to developing pelvic organ prolapse and urinary and faecal incontinence compared to nulliparous women or those who underwent caesarean section.
During the second stage of labour, the inferomedial portion of the levator ani muscle, pubococcygeal muscle, undergoes significant stretching, which can potentially result in injury to the pubovisceral muscle attachment (traumatic detachment) in 10-30% of cases. Pubovisceral muscle detachment has been proposed as a linking factor between vaginal delivery and pelvic organ prolapse.
The aims of this study are: 1) to evaluate the effects of the first vaginal delivery on the pelvic floor, investigating the actual incidence of levator ani muscle injuries in the postpartum period through a clinical and ultrasound diagnostic approach; 2) to correlate urogynecological clinical signs (pelvic floor hypertonicity, use of auxiliary muscle groups, command inversion) with postpartum symptom development, 3) to investigate a possible correlation between such muscular alterations and ultrasound abnormalities in order to identify possible indirect signs of partial or total clinically detectable muscle injury, 4) to correlate levator ani muscle injuries with intrapartum perineal outcomes, 5) to verify the actual higher incidence of injuries in patients who have had spontaneous laceration or episiotomy compared to patients with intact perineum.

This is a retrospective-prospective interventional study conducted between March 2021 and May 2023. All patients underwent a clinical and ultrasound urogynecological evaluation.
The inclusion criteria were term primiparous women, vaginal delivery (spontaneous or operative), spontaneous or induced labor, perineal outcomes including intact perineum, spontaneous laceration, or episiotomy.
The exclusion criteria were: multiparity, gestational age <37 weeks, fetal macrosomia (fetal weight exceeding 4500g), known neuromuscular or connective tissue pelvic pathologies (a strong risk factor for pelvic floor disorders).
Urogynecological evaluation was performed at least six weeks postpartum, considered the optimal timeframe to identify potential muscle injuries according to current literature data. During the examination, we evaluated the presence of urinary incontinence using the stress test, urogenital prolapse, urethral hypermobility assessed with the Q-tip test, and pubococcygeal muscle functionality using the PC test.
We also administered the FSDS and ICI-Q questionnaires to the patients to assess urinary incontinence and sexual dysfunction before and after childbirth.
A pelvic floor ultrasound with a 3D transvaginal probe was performed for an objective evaluation of the urogenital hiatus area and the possible presence of partial muscle lesions or avulsions of the levator ani muscle with a 3D endovaginal probe. Measurement of the hiatus area was conducted at rest, during contraction, and during the Valsalva manoeuvre. Any levator ani muscle injury was considered any discontinuity involving the pubococcygeal musculature, which was sonographically appreciated as a hypoechoic area interrupting the hyperechoic course of muscle fibres. Levator ani muscle avulsion was considered a clear interruption of the muscle fibres at their attachment point to the ischiopubic ramus, visible as a distinct anechoic area interrupting the course of muscle fibres.
We employed a comprehensive methodological approach, encompassing both univariate and bivariate analyses to examine the collected data. Bivariate analysis (t-test) was conducted to investigate relationships between two variables, enabling a deeper assessment of associations present in our dataset. We utilized the p-value as a measure of statistical significance to evaluate the importance of identified associations, considering p values less than 0.05 as statistically significant.

A total of 207 patients were recruited. In this population, the incidence of partial levator ani muscle lesions is 45% of the total sample, while the incidence of total LAM avulsions is 2.5%.
The incidence of symptoms and urogynecological signs collected during the examination were as follows: postpartum prolapse 54%, urinary incontinence 42%, dyspareunia rates at 18% prepartum and 30% postpartum, hypertonicity 24%, command inversion 28%, tenderness 21%. 
Ultrasound revealed partial injuries in 45% of cases, asymmetries in 0.5%, ballooning in 7%, and total avulsions in 2.5%.
Statistical significance was observed between the means of scores obtained from the ICIQ and FSDS questionnaires pre and postpartum (values significantly increased with a p-value < 0.01).
We assessed the correlation between questionnaire scores and perineal outcomes and found no difference in symptoms among episiotomy, intact perineum, and spontaneous laceration. We observed a correlation between ultrasound abnormalities and the presence of significant symptoms and signs. Our analysis revealed that perineal outcomes do not influence the development of internal muscle lesions. This aligns with literature data regarding the lack of usefulness of preventive episiotomy to avoid spontaneous laceration development.
Furthermore, we observed that patients with ultrasound heterogeneity clinically exhibited command inversion, and patients with muscle asymmetries on ultrasound exhibited hypertonicity. Statistical analysis also revealed that the areas of the urogenital hiatus, both at rest and during the Valsalva manoeuvre, correlate with hypertonicity. Consequently, larger hiatus areas, contrary to expectations, are found in patients with perineal hypertonicity. As literature indicates, larger urogenital hiatus areas compared to the average strongly correlate with pelvic floor disorders, especially prolapse onset.

Compared to previous beliefs, true avulsion of the levator ani muscle is actually much less common (2% vs. the 16% average reported in the literature).
The significant difference found in the incidence of levator ani muscle avulsions between our study and previous literature studies can be partially explained by the different modes of delivery undergone by the patients: in our sample, in fact, no patient underwent assisted delivery with forceps.
Moreover, in most of the literature studies, the ultrasound evaluation was performed transperineally with a convex probe, assessing the coronal and sagittal diameters of the hiatus and then reconstructing a 3D image. In our protocol, instead, the ultrasound evaluation was performed with a rotating 3D probe that scans the hiatus 360° transvaginally, in a neutral position, avoiding any pressure on the anterior or posterior vaginal walls. Consequently, the anatomy of the puborectal muscle is not influenced by compression. Despite minimal symptoms immediately postpartum, subtle muscle injuries were detected, emphasizing the importance of early detection for preventing future pelvic floor disorders.

We can conclude that after childbirth, the urogynecological profile of patients changes, as they begin to experience symptoms they had not previously encountered. Even in patients with small laceration or even with intact perineum, we observe small partial injuries of the levator ani muscle on ultrasound, which, at a macroscopic level, translate into incorrect muscular posture, manifested as hypertonicity or command inversion. This means that in most cases, six weeks postpartum, patients do not present overt prolapse or urinary incontinence, but the sensitivity and expertise of the urogynecologist in promptly detecting muscular abnormalities (hypertonicity) even indirectly (command inversion) can help prevent conditions such as prolapse and urinary incontinence, which may manifest later in those patients who exhibit larger areas and lesions on ultrasound. These results support the correlation between improper muscle usage and pelvic floor disorders.

Continence 12S (2024) 101444
DOI: 10.1016/j.cont.2024.101444