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Rotational instrumental deliveries are thought to carry additional risks compared with non-rotational instrumental deliveries, including trauma to maternal tissues, and require specific expertise and training. We conducted a retrospective study to investigate the association between the type of forceps delivery and maternal perineal trauma, and in particular to investigate if Kielland’s rotational forceps delivery increases obstetric anal sphincter injuries (OASIS).

This is a retrospective observational study of 1,515 women who attended a tertiary maternity unit over a period of 5 years and had operative vaginal deliveries primarily or completed by forceps. Data were obtained through the hospital’s maternity reporting system. The severity of maternal perineal trauma, particularly third and fourth-degree tears in relation to the type of forceps delivery was explored. Multinomial logistic regression models were used to estimate the crude and the adjusted relative risks (RR) of sustaining third-degree tears compared with other types of vaginal tears. Univariate analyses explored the crude associations between relative risks and age, ethnicity, birth weight, type of instrumental delivery and operator’s experience. A multivariate multinomial logistic regression model estimated the adjusted relative risks and included all the previous variables as independent covariates.

Of the 1,492 women included in the study, 150 women (77 %) had sustained category 1 tears, 63 women (4 %) had sustained category 2 tears and 279 women (19 %) had sustained third-degree tears. There was no statistically significant association between the severity of maternal perineal trauma and the type of forceps delivery (failed ventouse vs Kielland’s forceps RR 1.52, p = 0.159 CI 0.84-2.72, Wrigleys vs Kielland’s RR 0.59, p = 0.249, CI 0.24-1.43; Andersons vs Kielland’s RR 1.16, p = 0.603, CI 0.65-2.05) after adjusting for age, birth weight, BMI, ethnicity and operator experience (full list of covariates not included).

The incidence of third- and fourth-degree tears following rotational Kielland’s forceps delivery and other non-rotational forceps deliveries is comparable.