A dynamic prediction score for obstetric anal sphincter injury among nulliparous women delivering vaginally

In vivo measurement of the elastic properties of pelvic floor muscles in pregnancy using shear wave elastography

OBJECTIVE

We aimed to investigate changes in the elastic properties of levator ani muscle (LAM) and external anal sphincter (EAS) during pregnancy using shear wave elastography (SWE). Our secondary objective was to examine the association between the elastic properties of pelvic floor muscles (PFM) and perineal tears at childbirth.

METHODS

This was a prospective monocentric study, including nulliparous women. Three visits were planned (14-18, 24-28, and 34-38 weeks) with a SWE assessment of the LAM and EAS at rest and during Valsalva maneuver. Then, we collected data about the delivery's characteristics. Assessments were performed using an Aixplorer V12® device (SL 18-5 linear probe) using a transperineal approach, reporting the shear modulus in kPa. We looked for changes in PFM's elastic properties during pregnancy using one-way ANOVA for repeated measures. We compared the mean shear modulus in late pregnancy for each muscle and condition between women with an intact perineum at delivery and those with a perineal tear using Student's t test.

RESULTS

Forty-seven women were considered. Forty-five women had vaginal delivery of which 38 (84.4%) had perineal tears. We did not report any significant changes in the elastic properties of PFM during pregnancy. Women with an intact perineum at delivery had a stiffer EAS at Valsalva maneuver in late pregnancy (27.0 kPa vs. 18.2 kPa; p < 0.005).

CONCLUSIONS

There were no significant changes in the elastic properties of the PFM in pregnancy. Stiffer EAS in late pregnancy appears to be associated with a lower incidence of perineal tears.

Neonatal head circumference as a risk factor for obstetric anal sphincter injuries: a systematic review and meta-analysis

OBJECTIVE

Between 53% and 79% of women will sustain some degree of perineal laceration during vaginal delivery. Third- and fourth-degree perineal lacerations are known as obstetric anal sphincter injuries. Timely diagnosis and prompt treatment of obstetric anal sphincter injuries can help to prevent the development of severe consequences like fecal incontinence, urinary incontinence, and rectovaginal fistula. Neonatal head circumference is routinely measured postpartum but is often not mentioned as a risk factor for obstetric anal sphincter injuries in clinical guidelines. Thus far, no review article on the risk factors for obstetric anal sphincter injuries has discussed the role of neonatal head circumference. This study aimed to review and analyze the relationship between head circumference and the occurrence of obstetric anal sphincter injuries among previous studies to conclude whether head circumference should be recognized as an important risk factor.

DATA SOURCES

Through study screening on Google Scholar, PubMed, Scopus, and Science Direct for articles published between 2013 to 2023, followed by assessment of eligibility, this study ended up reviewing 25 studies, 17 of which were included in the meta-analysis.

STUDY ELIGIBILITY CRITERIA

Only studies that reported both the neonatal head circumference and the occurrence of obstetric anal sphincter injuries were included in this review.

METHODS

The included studies were appraised using the Dartmouth Library risk of bias assessment checklist. Qualitative synthesis was based on the study population, findings, adjusted confounding factors, and suggested causative links in each study. Quantitative synthesis was conducted using calculation and pooling of odds ratios and inverse variance using Review Manager 5.4.1.

RESULTS

A statistically significant association between head circumference and obstetric anal sphincter injuries was reported in 21 of 25 studies; 4 studies reported that head circumference was a true independent risk factor. A meta-analysis of the studies that reported neonatal head circumference as a dichotomous categorical variable with a cutoff point of 35±1 cm yielded statistically significant pooled results (odds ratio, 1.92; 95% confidence interval, 1.80-2.04).

CONCLUSION

The risk for obstetric anal sphincter injuries increased as the neonatal head circumference increased-this should be considered in decision-making during labor and postpartum management to attain the best outcome.

Risk factors for obstetric anal sphincter injury among nulliparous of advanced maternal age

OBJECTIVE

Data regarding the risk factors for obstetrical anal sphincter injury (OASI) among nulliparous advanced maternal age (AMA) women are scarce. We aimed to evaluate the risk factors and the rate of OASI in this population.

METHODS

A retrospective case-control study of nulliparous women aged ≥35 who delivered vaginally between March 2011 and August 2021. The study cohort included nulliparous AMA women, aged 35 years or older, delivering vaginally a singleton, vertex neonate. We excluded cases with missing data. Maternal and intrapartum characteristics were compared between OASI and no-OASI groups. We matched groups to the earliest gestational age in which OASI has occurred.

RESULTS

A total of 3,635 women met inclusion criteria. Mean age of the participants was 38 years (range 35-56, interquartile range 36-39). The oldest age in which an OASI was diagnosed was 45. A total of 55 (1.5%) cases of OASI were diagnosed. Gestational age at delivery was higher in the OASI group compared to the no-OASI group (mean 39^6/7±1^2/7 vs. 39^1/7±2^3/7 weeks respectively, p=.039). The rate of induction of labor, oxytocin and epidural analgesia, prolonged second stage, mode of delivery, and rate of blood transfusion did not vary between groups. Estimated fetal weight was higher in the OASI group (3,324 ± 308 vs. 3,114 ± 566 g, p<.001). Sonographic abdominal circumference was higher in the OASI group (338 ± 13 vs. 328 ± 28 mm, p<.001). Mean birthweight was higher in the OASI group (3,286 ± 400 vs. 3,059 ± 541 g, p=.002) and the birthweight centile was higher as well (60 ± 26 vs. 52 ± 25, p=.024).In a multivariable regression analysis including birthweight, gestational age, operative vaginal delivery, epidural anesthesia, and hypertensive disorders-birthweight and hypertensive disorder were positively associated with an OASI odds ratio [OR 95% CI 1.6 (1.1-2.32) for every 500 g increase; 2.42 (1.006-5.82), respectively]. Epidural anesthesia was negatively associated with OASI [OR 95% CI 0.49) 0.27-0.87)].

CONCLUSIONS

Epidural anesthesia is the only modifiable risk factor and is protective against OASI among nulliparous AMA women. Birthweight and hypertensive disorders are also independent predictors of OASI in this population.