Research Letter

Levator ani defect severity and its association with enlarged hiatus size, levator bowl depth, and prolapse size

Pelvic floor disorders after childbirth have distressing lifelong consequences for women, requiring more than 300,000 women to have surgery annually. This represents approximately 10% of the 3 million women who give birth vaginally each year. Vaginal birth is the largest modifiable risk factor for prolapse, the pelvic floor disorder most strongly associated with birth, and is an important contributor to stress incontinence. These disorders require 10 times as many operations as anal sphincter injuries. Imaging shows that injuries of the levator ani muscle, perineal body, and membrane occur in up to 19% of primiparous women. During birth, the levator muscle and birth canal tissues must stretch to more than 3 times their original length; it is this overstretching that is responsible for the muscle tear visible on imaging rather than compression or neuropathy. The injury is present in 55% of women with prolapse later in life, with an odds ratio of 7.3, compared with women with normal support. In addition, levator damage can affect other aspects of hiatal closure, such as the perineal body and membrane. These injuries are associated with an enlarged urogenital hiatus, now known as antedate prolapse, and with prolapse surgery failure. Risk factors for levator injury are multifactorial and include forceps delivery, occiput posterior birth, older maternal age, long second stage of labor, and birthweight of >4000 g. Delivery with a vacuum device is associated with reduced levator damage. Other steps that might logically reduce injuries include manual rotation from occiput posterior to occiput anterior, slow gradual delivery, perineal massage or compresses, and early induction of labor, but these require study to document protection. In addition, teaching women to avoid pushing against a contracted levator muscle would likely decrease injury risk by decreasing tension on the vulnerable muscle origin. Providing care for women who have experienced difficult deliveries can be enhanced with early recognition, physical therapy, and attention to recovery. It is only right that women be made aware of these risks during pregnancy. Educating women on the long-term pelvic floor sequelae of childbirth should be performed antenatally so that they can be empowered to make informed decisions about management decisions during labor.

This study investigated the predicting value of the ratio of levator hiatus diameter (LHS) to fetal head circumference (HC) in pregnant women at 37 weeks of gestation in the progression of the second stage of labor and levator ani injury 6 weeks postpartum.

A total of 120 first-time women who gave vaginal delivery at 37 weeks of pregnancy were selected as the subjects in our hospital during March 2021 to March 2022. The subjects were divided into the second stage of labor > 1 h group and the second stage of labor ≤ 1 h group, according to the delivery time of the second stage of labor. According to the 6-week postpartum follow-up ultrasound examination with or without levator ani injury, they were divided into levator ani injury group and no injury group. All primipara women underwent three-dimensional ultrasonography at 37 weeks of gestation, and the resting LHS, Valsalva LHS, fetal HC and the ratio of resting LHS and fetal HC were compared. The correlation between these factors and the length of the second labor stage was analyzed using Pearson correlation analysis. The value of these factors in predicting labor progression and postpartum levator ani injury was assessed by receiver operating characteristic (ROC) curves.

The resting LHS, Valsalva LHS and the ratio of resting LHS and fetal HC in the levator ani injury group were lower than these in the no injury group, while fetal HC in the levator ani injury group was higher than that in the no injury group (P < 0.05). The resting LHS, Valsalva LHS and the ratio of resting LHS and fetal HC in the second stage of labor > 1 h group were lower than these in the second stage of labor ≤ 1 h group, while fetal HC in the second stage of labor > 1 h group was higher than that in the second stage of labor ≤ 1 h group (P < 0.05). A significant negative correlation was observed between resting LHS/HC and total labor process (=-0.333, P < 0.01). ROC curve analysis showed that the AUCs of resting LHS, Valsalva LHS, HC, and resting LHS/HC ratio in predicting prolongation of the second stage of labor were 0.741, 0.740, 0.702, and 0.843 respectively. Besides, the AUCs of resting LHS, Valsalva LHS, HC, and resting LHS/HC ratio in predicting the total labor process were 0.657, 0.684, 0.768, and 0.836 respectively. The AUCs of resting LHS, Valsalva LHS, HC, and resting LHS/HC ratio in predicting postpartum levator ani muscle injury were 0.769, 0.773, 0.747, and 0.885 respectively.These results suggested that the ratio of resting LHS and fetal HC may have certain clinical value in predicting levator ani injury in pregnant women.

LHS, fetal HC and the ratio of resting LHS and fetal HC are significantly correlated with labor progression and postpartum levator ani injury, which have certain value in predicting labor progress and postpartum levator ani injury. Therein, the ratio of resting LHS and fetal HC has the highest predictive value, and early detection of the ratio of resting LHS and fetal HC is helpful to guide the selection of appropriate delivery mode.