The impact of maternal body mass index on the rate of obstetric anal sphincter injury in nulliparous women: A Victorian retrospective cohort study

Abstract

BackgroundMaternal obesity is an important comorbidity in contemporary obstetrics practice and is associated with significantly increased perinatal complications. Obstetric anal sphincter injury (OASIS) sustained during labour can lead to faecal incontinence, chronic pain and effects on quality of life. Currently, it is unclear if maternal body mass index (BMI) influences the risk of sustaining OASIS.AimTo investigate the impact of increased BMI on the rate of OASIS among nulliparous women.Materials and MethodsA retrospective cohort study was conducted, which included nulliparous women with singleton, vaginal deliveries ≥37 weeks gestation at a Victorian regional centre between 2007 and 2017 (n = 3335). Logistic regression was performed to calculate unadjusted and adjusted odds ratios (aOR). Women were grouped by World Health Organization BMI categories, and the rates of OASIS were evaluated.ResultsWomen with a BMI ≥ 25 were significantly less likely to develop OASIS compared to women with a BMI < 25 (aOR 0.60, 95% CI 0.41–0.89). Women with a BMI ≥ 35 had significantly decreased odds of OASIS compared to normal weight women (aOR 0.27, 0.10–0.78). While not statistically significant, the odds of OASIS decreased with each increase in BMI class. Other statistically significant risk factors were maternal age, birth weight, forceps delivery, non‐smokers (aOR 4.03, 1.46–11.1) and diabetes mellitus (aOR 9.48, 2.1–41.4).ConclusionWomen with a BMI ≥ 25 were less likely to sustain OASIS compared to women with a BMI < 25. Furthermore, the odds of OASIS decreased for each increase in BMI category. These findings warrant further investigation into the mechanism of this protective effect.

Obstetric anal sphincter injuries—Maternal, fetal and sociodemographic risk factors: A retrospective register‐based study

“…Increasing BMI showed a decreased risk of OASIS in the crude analysis; however, it was only apparent in the adjusted model after adding birthweight to the analysis. A decreased risk of OASIS associated with increased BMI has been shown in several previous studies 6,16–18 . However, all previously mentioned studies either adjusted for birthweight or excluded cases with babies heavier than 4000 g at birth in order to find this positive association.…”

“…A decreased risk of OASIS associated with increased BMI has been shown in several previous studies. 6 , 16 , 17 , 18 However, all previously mentioned studies either adjusted for birthweight or excluded cases with babies heavier than 4000 g at birth in order to find this positive association. When interpreting our results, one must consider that obese women are at higher risk of giving birth to larger babies.…”

The impact of maternal body mass index on pelvic floor during labor and after childbirth, and a new anesthetic approach for repair of perineal lacerations

“…Several of the risk factors for OASI, such as primiparity, instrumental delivery, macrosomia and prolonged duration of the second stage of labor can all be affected by maternal BMI 23,64,65 . This is of interest since several reports conclude that overweight and obese women seem to have a decreased risk for OASI compared to women with normal weight 3,4,66 . High maternal age and ethnicity are also described as risk factors for OASIs 67 .…”

Maternal overweight and obesity : impact on obstetric outcomes in adolescents and oxytocin in labor

“…49,50 By contrast, the risk for obstetric anal sphincter injury (OASI) seems to be decreased in overweight and obese women. [55][56][57] The reasons for this are speculative, but increased perineal thickness, more stretchable tissue due to adiposity or sub diagnostics caused by more difficult examination of the obese women have been suggested. [55][56][57][58] Regarding neonatal outcomes, overweight and obesity have been associated with increased risks for large for gestational age (LGA) and macrosomia.…”