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BMJ Open. 2014 Jul 24;4(7):e004592. doi: 10.1136/bmjopen-2013-004592.

Assessing the association of oxytocin augmentation with obstetric anal sphincter injury in nulliparous women: a population-based, case-control study.

Author information

1
Department of Obstetrics and Gynecology, Stavanger University Hospital, Stavanger, Norway Department of Clinical Medicine I, University of Bergen, Bergen, Norway.
2
Women's Health and Perinatology Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway.
3
Department of Clinical Medicine I, University of Bergen, Bergen, Norway Department of GI Surgery, Stavanger University Hospital, Stavanger, Norway.
4
Department of Obstetrics and Gynecology, Stavanger University Hospital, Stavanger, Norway National Center for Fetal Medicine, Trondheim University Hospital (St Olavs Hospital), Trondheim, Norway.

Abstract

OBJECTIVE:

To assess the association of oxytocin augmentation with obstetric anal sphincter injury among nulliparous women.

DESIGN:

Population-based, case-control study.

SETTING:

Primary and secondary teaching hospital serving a Norwegian region.

POPULATION:

15 476 nulliparous women with spontaneous start of labour, single cephalic presentation and gestation ≥37 weeks delivering vaginally between 1999 and 2012.

METHODS:

Based on the presence or absence of oxytocin augmentation, episiotomy, operative vaginal delivery and birth weight (<4000 vs ≥4000 g), we modelled in logistic regression the best fit for prediction of anal sphincter injury. Within the modified model of main exposures, we tested for possible confounding, and interactions between maternal age, ethnicity, occiput posterior position and epidural analgaesia.

MAIN OUTCOME MEASURE:

Obstetric anal sphincter injury.

RESULTS:

Oxytocin augmentation was associated with a higher OR of obstetric anal sphincter injuries in women giving spontaneous birth to infants weighing <4000 g (OR 1.8; 95% CI 1.5 to 2.2). Episiotomy was not associated with sphincter injuries in spontaneous births, but with a lower OR in operative vaginal deliveries. Spontaneous delivery of infants weighing ≥4000 g was associated with a threefold higher OR, and epidural analgaesia was associated with a 30% lower OR in comparison to no epidural analgaesia.

CONCLUSIONS:

Oxytocin augmentation was associated with a higher OR of obstetric anal sphincter injuries during spontaneous deliveries of normal-size infants. We observed a considerable effect modification between the most important factors predicting anal sphincter injuries in the active second stage of labour.

KEYWORDS:

Epidemiology

PMID:
25059967
PMCID:
PMC4120359
DOI:
10.1136/bmjopen-2013-004592
[Indexed for MEDLINE]
Free PMC Article

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