Maternal body mass index and risk of obstetric anal sphincter injury.
OBJECTIVE
To estimate the association between maternal obesity and risk of three different degrees of severity of obstetric anal sphincter injury.


METHODS
The study population consisted of 436,482 primiparous women with singleton term vaginal cephalic births between 1998 and 2011 identified in the Swedish Medical Birth Registry. Women were grouped into six categories of BMI. BMI 18.5-24.9 was set as reference. Primary outcome was third-degree perineal laceration, partial or total, and fourth-degree perineal laceration. Adjustments were made for year of delivery, maternal age, fetal head position at delivery, infant birth weight and instrumental delivery.


RESULTS
The overall prevalence of third- or four-degree anal sphincter injury was 6.6% (partial anal sphincter injury 4.6%, total anal sphincter injury 1.2%, unclassified as either partial and total 0.2%, or fourth degree lacerations 0.6%). The risk for a partial, total, or a fourth-degree anal sphincter injury decreased with increasing maternal BMI most pronounced for total anal sphincter injury where the risk among morbidly obese women was half that of normal weight women, OR 0.47 95% CI 0.28-0.78.


CONCLUSIONS
Obese women had a favourable outcome compared to normal weight women concerning serious pelvic floor damages at birth.
Department of Obstetrics and Gynaecology and Department of Clinical and Experimental Medicine, Linköping University, 581 85 Linköping, Sweden.
Marie
0000-0003-4679-550X
M
Blomberg
D001003:Anal Canal / Q000293:injuries*; D015992:Body Mass Index; D036861:Delivery, Obstetric / Q000009:adverse effects*; D005260:Female; D006801:Humans; D022125:Lacerations / Q000453:epidemiology* / Q000209:etiology; D009767:Obesity, Morbid / Q000453:epidemiology*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*