Int Urogynecol J (2015) 26:1525–1532 DOI 10.1007/s00192-015-2717-6
ORIGINAL ARTICLE
Kielland’s forceps: does it increase the risk of anal sphincter injuries? An observational study Nivedita Gauthaman 1 & Denise Henry 1 & Irina Chis Ster 2 & Azar Khunda 3 & Stergios K. Doumouchtsis 1
Received: 18 September 2014 / Accepted: 15 April 2015 / Published online: 20 May 2015 # The International Urogynecological Association 2015
Abstract Introduction and hypothesis Rotational instrumental deliveries are thought to carry additional risks compared with nonrotational 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). Methods 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. Results 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). Conclusions The incidence of third- and fourth-degree tears following rotational Kielland’s forceps delivery and other non-rotational forceps deliveries is comparable.
* Nivedita Gauthaman [email protected]
Abbreviations OASIS Obstetric anal sphincter injuries RR Relative risk
Keywords Kielland’s forceps . Rotational forceps delivery . Third-degree tears
1
Department of Obstetrics and Gynaecology, St George’s University Hospitals NHS Foundation Trust, London, UK
2
Biostatistics, Department of Clinical Sciences, St George’s University of London, London, UK
Introduction
3
Department of Obstetrics and Gynaecology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK
There is no consensus about the place of Kielland’s forceps in modern obstetrics. Kielland’s forceps are used to achieve
1526
rotation of the fetal head from the occipito-transverse or occipito-posterior position at the mid-cavity level of the pelvis. Ventouse can be used in these situations as well; however, there is a risk of failure and subsequent use of sequential instruments [1, 2] with added maternal and neonatal morbidity. Over the past 20 years the rising trend in the usage of vacuum extractor and more liberal use of caesarean sections have resulted in the steady decline of forceps deliveries [3–5]. There are also other factors such as fear of complications and subsequent litigation [6, 7], lack of experience with modern obstetric training and increasing obstetrician’s preference to resort to caesarean sections in the second stage [8–11], which has led to the decline in the use of Kielland’s forceps. Concerns related to the use of Kielland’s forceps are historically attributed to observational studies reporting adverse outcomes to the mother and fetus [12, 13]. However, there is no definitive evidence that the use of Kielland’s forceps adversely affects the baby’s long-term development [14]. With appropriate use of Kielland’s forceps by skilled obstetricians there was no evidence to show any detrimental fetal effects [14]. The increase in maternal morbidity due to forceps delivery, not specifically Kielland’s, can be attributed to vaginal lacerations, injury to the external anal sphincter or rectal mucosa [15] and vulvovaginal haematomas. We hypothesised that Kielland’s rotational forceps delivery does not increase the severity of maternal perineal trauma. The rotation of the fetal head occurs at the mid-cavity level and therefore should not increase the risk of perineal trauma significantly over other types of forceps deliveries. The objective of this study was to investigate whether there is an association between maternal perineal trauma and the type of forceps delivery, and in particular to investigate whether Kielland’s rotational forceps delivery increases the risk of OASIS. Although not the primary aim of the study, we also looked at the trends in the OASIS related to factors such as age, BMI, smoking status, parity and gestational age.
Materials and methods This observational study was conducted at St George’s Hospital, London as a part of hospital service evaluation. Our consultant-led maternity unit has an average of 5,000 deliveries per year. The annual percentage of operative vaginal deliveries during the period of the study was 15 %, which is in line with the UK national rate [15, 16]. The types of instruments used were Kielland’s forceps for rotational instrumental deliveries and direct traction forceps (Anderson’s, Wrigley’s forceps). This was a retrospective observational study using data retrieved from the hospital’s electronic management system. The data were entered by midwives who cared for these women at the time of delivery and retrieved electronically by our
Int Urogynecol J (2015) 26:1525–1532
audit manager. The administrators regularly verified the correctness of data entry by cross checking with the patient’s delivery notes whenever a third-degree tear was recorded in the maternity database. We did not procure the maternity records for this study as all the required fields were completed, with only 1.5 % missing data. One thousand five hundred and fifteen consecutive women with singleton pregnancies who were delivered by forceps in the maternity unit of St Georges Hospital between March 2007 and October 2012 were obtained from the hospital’s electronic maternity reporting system. We chose the 5-year period up to the point when we had complete and cross-checked data. Our inclusion criteria were all forceps deliveries within the time period with singleton live pregnancies and cephalic presentation of more than 36 weeks’ gestation. As the primary focus of this study was to investigate the severity of perineal trauma in relation to forceps deliveries we excluded successful ventouse deliveries (9.8 % of all deliveries in the study period) in this cohort. As most of the studies comparing Kielland’s with other types of forceps have extensively evaluated fetal outcome we did not feel it was necessary to include it in our study. We wanted to specifically evaluate a possible difference in the perineal trauma in relation to the rotational vs non-rotational forceps and therefore focussed on this aspect alone. Kielland’s forceps deliveries constituted 0.4 %, failed ventouse leading to forceps deliveries 1.7 % and other forceps deliveries 4 % of all deliveries during the time period of the study. Demographic data such as age, parity, ethnicity, smoking at booking, booking BMI, labour analgesia, type of forceps delivery, gestational age, birth weight at delivery and operator experience were obtained from the database (Table 1). We classified the degrees of perineal trauma severity into three categories (Table 2). Category 1 consisted of first- and second-degree perineal tears and episiotomies, which is the baseline level of perineal trauma usually expected with any type of instrumental delivery. Category 2 consisted of vaginal lacerations, extended episiotomies, cervical and labial tears that occurred in addition to the episiotomies. Category 3 consisted of third- and fourth-degree perineal tears, which can be associated with long-term implications such as faecal and flatal incontinence, and sexual and pelvic floor dysfunction. Demographic and obstetric variables were analysed and summarised according to their nature (continuous or nominal) and appropriate means/standard deviations/proportions were calculated. Multinomial logistic regression models were fitted to the data to estimate the crude and the adjusted relative risks (RR) of sustaining category 2 or 3 perineal trauma vs category 1. Univariate analyses explored these 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. Potential interactions between the
Int Urogynecol J (2015) 26:1525–1532 Table 1
1527
Patient demographics
Demographics
Kielland’s forceps delivery (n=108)
Failed ventouse (FV) leading to forceps delivery (n=494)
Direct traction forceps (n=890) Wrigley’s (W) (n=90)
Anderson’s (A) (n=800)
Age (mean/SD)
31.11/5.309
31.17/5.085
31.15/5.596
30.94/ 5.032
BMI (mean/SD) Smoking status
25.13/4.287 1 (1 %)
23.88/3.808 10 (2 %)
24.58/5.072 2 (2 %)
24.33/4.221 32 (4 %)
18 (17 %)
79 (16 %)
18 (20 %)
152 (19 %)
89 (82 %)
405 (82 %)
70 (78 %)
616 (77 %)
71 (66 %)
310 (63 %)
67 (74 %)
524 (65 %)
25 (23 %)
106 (21 %)
11 (12 %)
156 (20 %)
3 (3 %) 9 (8 %)
25 (5 %) 53 (11 %)
6 (7 %) 6 (7 %)
42 (5 %) 78 (10 %)
97 (90 %) 11 (10 %)
451 (91 %) 43 (9 %)
80 (89 %) 10 (11 %)
724 (91 %) 76 (9 %)
3,461/426.83
3,508/466.27
3,480/436.31
3,443/ 498.24
40.1/1.45
40.2/1.46
40.02/1.67
40.05/1.61
Regional Non-regional Consultant Senior registrar (SR)
95 (89 %) 13 (11 %) 50 (47 %) 22 (20 %)
397 (80 %) 97 (20 %) 48 (10 %) 170 (34 %)
76 (84 14 (16 13 (14 34 (38
%) %) %) %)
681 (85 %) 119 (15 %) 87 (10 %) 268 (34 %)
Junior registrar (JR)
36 (33 %)
276 (56 %)
43 (48 %)
445 (56 %)
Ethnicity
Parity Birth weight, mean (g)/SD Gestational age, mean/SD Analgesia Grade of operator
Smoking Stopped at booking Non-smoker White British /European Asian/Asian British(Indian, Sri Lankan, Pakistani, Chinese origins) Black/Black British Others (other ethnicities, mixed race) Primi Multi
covariates have also been examined. Episiotomy is often considered a significant risk factor for OASIS. However, episiotomy is performed electively in the vast majority of forceps deliveries. Indeed, in our series episiotomy was performed in 82 % of rotational and 84 % of non-rotational forceps deliveries (p=0.66). For this reason we did not include episiotomy as a covariate in our multivariate analysis. Parameter estimates with p values less than 0.05 were considered as having a statistically significant effect and the RR estimates and the corresponding 95 % confidence intervals (CI) were calculated. All statistical analyses were performed using STATA (Stata Statistical Software: Release 13; Statacorp, College Station, TX, USA). The primary outcome measure was to investigate the various degrees of perineal trauma, especially OASIS in relation to the different types of forceps delivery. We also investigated the extent to which this association is affected by various factors such as age, BMI, ethnicity and birth weight, which are deemed to be potential confounders likely to influence the risk of OASIS in our study cohort. Ethnicity was categorised
as White, Asian/Asian British, Black/Black British and other. These are the four main categories used in the 2011 census, and these ethnicities are commonly considered in other studies and allow for easy comparison. The study was registered with the St Georges NHS Trust Audit Department. Formal ethical approval was not sought as the study was classified as service evaluation under current UK regulations.
Results The original cohort consisted of 1,525 women. We excluded 10 (0.06 %) women who had no clinically relevant perineal trauma. The remaining cohort of 1,515 women were evaluated with regards to the category of perineal trauma in relation to the mode of delivery and all other potential confounders. 98.5 % of women (1,492) had all data variables complete and the analysis is based on these data. A sensitivity analysis was carried out on all data, assuming that missing variables are missing completely at random (MAR) did not change the estimates
1528 Table 2
Int Urogynecol J (2015) 26:1525–1532 Types of perineal trauma
Perineal trauma
Kielland’s forceps delivery (n=108)
Failed ventouse leading to forceps delivery (n=494)
Direct traction forceps delivery (n=890) Wrigley’s Anderson’s (n=90) (n=800)
Category 1(first-/second-degree tears, episiotomies)
87 (80 %)
Category 2 (cervical, vaginal lacerations and labial tears, and 3 (3 %) episiotomy extensions) Category 3 (third- and fourth-degree perineal tears) 18 (17 %)
(results not shown). One hundred and eight women (7 %) had Kielland’s rotational forceps delivery, 890 women (60 %) had non-rotational direct traction forceps delivery, among which 800 women (54 %) had Anderson’s forceps delivery and 90 women (6 %) had Wrigley’s forceps delivery. Four hundred and ninety-four women (33 %) had failed ventouse delivery (Kiwi Omnicup) leading to the use of direct forceps to complete the delivery. Figure 1 shows the flowchart for the type of forceps deliveries in our cohort. Figures 2, 3 and 4 illustrate the distribution of age, BMI, and birth weight in our study population. Of the 1,492 women included in the study, 1,150 women (77 %) had sustained category 1 tears, 63 women (4 %) had sustained category 2 tears and 279 women (19 %) had sustained third-degree tears. The adjusted effect of each covariate on the relative risk (RR) ratio is interpreted given that the other variables in the model were held constant. The relative risk of third-/fourthdegree tears vs category 1 injury decreased by a factor of 0.96 (0.93–0.98) for every 1 year increase in the age, which was statistically significant (p=0.002). For every 5 - year increase in the women’s age, the RR of third-/fourth-degree tear vs category 1 injury decreased by a factor of 0.80 (0.70, 0.92), which was statistically significant (p=0.002). The relative risk ratio for third/fourth degree tears vs category 1 damage increased by a factor of 1.31 (1.14–1.52) with every 500-g increase in birth weight, which was statistically significant (p
ORIGINAL ARTICLE
Kielland’s forceps: does it increase the risk of anal sphincter injuries? An observational study Nivedita Gauthaman 1 & Denise Henry 1 & Irina Chis Ster 2 & Azar Khunda 3 & Stergios K. Doumouchtsis 1
Received: 18 September 2014 / Accepted: 15 April 2015 / Published online: 20 May 2015 # The International Urogynecological Association 2015
Abstract Introduction and hypothesis Rotational instrumental deliveries are thought to carry additional risks compared with nonrotational 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). Methods 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. Results 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). Conclusions The incidence of third- and fourth-degree tears following rotational Kielland’s forceps delivery and other non-rotational forceps deliveries is comparable.
* Nivedita Gauthaman [email protected]
Abbreviations OASIS Obstetric anal sphincter injuries RR Relative risk
Keywords Kielland’s forceps . Rotational forceps delivery . Third-degree tears
1
Department of Obstetrics and Gynaecology, St George’s University Hospitals NHS Foundation Trust, London, UK
2
Biostatistics, Department of Clinical Sciences, St George’s University of London, London, UK
Introduction
3
Department of Obstetrics and Gynaecology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK
There is no consensus about the place of Kielland’s forceps in modern obstetrics. Kielland’s forceps are used to achieve
1526
rotation of the fetal head from the occipito-transverse or occipito-posterior position at the mid-cavity level of the pelvis. Ventouse can be used in these situations as well; however, there is a risk of failure and subsequent use of sequential instruments [1, 2] with added maternal and neonatal morbidity. Over the past 20 years the rising trend in the usage of vacuum extractor and more liberal use of caesarean sections have resulted in the steady decline of forceps deliveries [3–5]. There are also other factors such as fear of complications and subsequent litigation [6, 7], lack of experience with modern obstetric training and increasing obstetrician’s preference to resort to caesarean sections in the second stage [8–11], which has led to the decline in the use of Kielland’s forceps. Concerns related to the use of Kielland’s forceps are historically attributed to observational studies reporting adverse outcomes to the mother and fetus [12, 13]. However, there is no definitive evidence that the use of Kielland’s forceps adversely affects the baby’s long-term development [14]. With appropriate use of Kielland’s forceps by skilled obstetricians there was no evidence to show any detrimental fetal effects [14]. The increase in maternal morbidity due to forceps delivery, not specifically Kielland’s, can be attributed to vaginal lacerations, injury to the external anal sphincter or rectal mucosa [15] and vulvovaginal haematomas. We hypothesised that Kielland’s rotational forceps delivery does not increase the severity of maternal perineal trauma. The rotation of the fetal head occurs at the mid-cavity level and therefore should not increase the risk of perineal trauma significantly over other types of forceps deliveries. The objective of this study was to investigate whether there is an association between maternal perineal trauma and the type of forceps delivery, and in particular to investigate whether Kielland’s rotational forceps delivery increases the risk of OASIS. Although not the primary aim of the study, we also looked at the trends in the OASIS related to factors such as age, BMI, smoking status, parity and gestational age.
Materials and methods This observational study was conducted at St George’s Hospital, London as a part of hospital service evaluation. Our consultant-led maternity unit has an average of 5,000 deliveries per year. The annual percentage of operative vaginal deliveries during the period of the study was 15 %, which is in line with the UK national rate [15, 16]. The types of instruments used were Kielland’s forceps for rotational instrumental deliveries and direct traction forceps (Anderson’s, Wrigley’s forceps). This was a retrospective observational study using data retrieved from the hospital’s electronic management system. The data were entered by midwives who cared for these women at the time of delivery and retrieved electronically by our
Int Urogynecol J (2015) 26:1525–1532
audit manager. The administrators regularly verified the correctness of data entry by cross checking with the patient’s delivery notes whenever a third-degree tear was recorded in the maternity database. We did not procure the maternity records for this study as all the required fields were completed, with only 1.5 % missing data. One thousand five hundred and fifteen consecutive women with singleton pregnancies who were delivered by forceps in the maternity unit of St Georges Hospital between March 2007 and October 2012 were obtained from the hospital’s electronic maternity reporting system. We chose the 5-year period up to the point when we had complete and cross-checked data. Our inclusion criteria were all forceps deliveries within the time period with singleton live pregnancies and cephalic presentation of more than 36 weeks’ gestation. As the primary focus of this study was to investigate the severity of perineal trauma in relation to forceps deliveries we excluded successful ventouse deliveries (9.8 % of all deliveries in the study period) in this cohort. As most of the studies comparing Kielland’s with other types of forceps have extensively evaluated fetal outcome we did not feel it was necessary to include it in our study. We wanted to specifically evaluate a possible difference in the perineal trauma in relation to the rotational vs non-rotational forceps and therefore focussed on this aspect alone. Kielland’s forceps deliveries constituted 0.4 %, failed ventouse leading to forceps deliveries 1.7 % and other forceps deliveries 4 % of all deliveries during the time period of the study. Demographic data such as age, parity, ethnicity, smoking at booking, booking BMI, labour analgesia, type of forceps delivery, gestational age, birth weight at delivery and operator experience were obtained from the database (Table 1). We classified the degrees of perineal trauma severity into three categories (Table 2). Category 1 consisted of first- and second-degree perineal tears and episiotomies, which is the baseline level of perineal trauma usually expected with any type of instrumental delivery. Category 2 consisted of vaginal lacerations, extended episiotomies, cervical and labial tears that occurred in addition to the episiotomies. Category 3 consisted of third- and fourth-degree perineal tears, which can be associated with long-term implications such as faecal and flatal incontinence, and sexual and pelvic floor dysfunction. Demographic and obstetric variables were analysed and summarised according to their nature (continuous or nominal) and appropriate means/standard deviations/proportions were calculated. Multinomial logistic regression models were fitted to the data to estimate the crude and the adjusted relative risks (RR) of sustaining category 2 or 3 perineal trauma vs category 1. Univariate analyses explored these 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. Potential interactions between the
Int Urogynecol J (2015) 26:1525–1532 Table 1
1527
Patient demographics
Demographics
Kielland’s forceps delivery (n=108)
Failed ventouse (FV) leading to forceps delivery (n=494)
Direct traction forceps (n=890) Wrigley’s (W) (n=90)
Anderson’s (A) (n=800)
Age (mean/SD)
31.11/5.309
31.17/5.085
31.15/5.596
30.94/ 5.032
BMI (mean/SD) Smoking status
25.13/4.287 1 (1 %)
23.88/3.808 10 (2 %)
24.58/5.072 2 (2 %)
24.33/4.221 32 (4 %)
18 (17 %)
79 (16 %)
18 (20 %)
152 (19 %)
89 (82 %)
405 (82 %)
70 (78 %)
616 (77 %)
71 (66 %)
310 (63 %)
67 (74 %)
524 (65 %)
25 (23 %)
106 (21 %)
11 (12 %)
156 (20 %)
3 (3 %) 9 (8 %)
25 (5 %) 53 (11 %)
6 (7 %) 6 (7 %)
42 (5 %) 78 (10 %)
97 (90 %) 11 (10 %)
451 (91 %) 43 (9 %)
80 (89 %) 10 (11 %)
724 (91 %) 76 (9 %)
3,461/426.83
3,508/466.27
3,480/436.31
3,443/ 498.24
40.1/1.45
40.2/1.46
40.02/1.67
40.05/1.61
Regional Non-regional Consultant Senior registrar (SR)
95 (89 %) 13 (11 %) 50 (47 %) 22 (20 %)
397 (80 %) 97 (20 %) 48 (10 %) 170 (34 %)
76 (84 14 (16 13 (14 34 (38
%) %) %) %)
681 (85 %) 119 (15 %) 87 (10 %) 268 (34 %)
Junior registrar (JR)
36 (33 %)
276 (56 %)
43 (48 %)
445 (56 %)
Ethnicity
Parity Birth weight, mean (g)/SD Gestational age, mean/SD Analgesia Grade of operator
Smoking Stopped at booking Non-smoker White British /European Asian/Asian British(Indian, Sri Lankan, Pakistani, Chinese origins) Black/Black British Others (other ethnicities, mixed race) Primi Multi
covariates have also been examined. Episiotomy is often considered a significant risk factor for OASIS. However, episiotomy is performed electively in the vast majority of forceps deliveries. Indeed, in our series episiotomy was performed in 82 % of rotational and 84 % of non-rotational forceps deliveries (p=0.66). For this reason we did not include episiotomy as a covariate in our multivariate analysis. Parameter estimates with p values less than 0.05 were considered as having a statistically significant effect and the RR estimates and the corresponding 95 % confidence intervals (CI) were calculated. All statistical analyses were performed using STATA (Stata Statistical Software: Release 13; Statacorp, College Station, TX, USA). The primary outcome measure was to investigate the various degrees of perineal trauma, especially OASIS in relation to the different types of forceps delivery. We also investigated the extent to which this association is affected by various factors such as age, BMI, ethnicity and birth weight, which are deemed to be potential confounders likely to influence the risk of OASIS in our study cohort. Ethnicity was categorised
as White, Asian/Asian British, Black/Black British and other. These are the four main categories used in the 2011 census, and these ethnicities are commonly considered in other studies and allow for easy comparison. The study was registered with the St Georges NHS Trust Audit Department. Formal ethical approval was not sought as the study was classified as service evaluation under current UK regulations.
Results The original cohort consisted of 1,525 women. We excluded 10 (0.06 %) women who had no clinically relevant perineal trauma. The remaining cohort of 1,515 women were evaluated with regards to the category of perineal trauma in relation to the mode of delivery and all other potential confounders. 98.5 % of women (1,492) had all data variables complete and the analysis is based on these data. A sensitivity analysis was carried out on all data, assuming that missing variables are missing completely at random (MAR) did not change the estimates
1528 Table 2
Int Urogynecol J (2015) 26:1525–1532 Types of perineal trauma
Perineal trauma
Kielland’s forceps delivery (n=108)
Failed ventouse leading to forceps delivery (n=494)
Direct traction forceps delivery (n=890) Wrigley’s Anderson’s (n=90) (n=800)
Category 1(first-/second-degree tears, episiotomies)
87 (80 %)
Category 2 (cervical, vaginal lacerations and labial tears, and 3 (3 %) episiotomy extensions) Category 3 (third- and fourth-degree perineal tears) 18 (17 %)
(results not shown). One hundred and eight women (7 %) had Kielland’s rotational forceps delivery, 890 women (60 %) had non-rotational direct traction forceps delivery, among which 800 women (54 %) had Anderson’s forceps delivery and 90 women (6 %) had Wrigley’s forceps delivery. Four hundred and ninety-four women (33 %) had failed ventouse delivery (Kiwi Omnicup) leading to the use of direct forceps to complete the delivery. Figure 1 shows the flowchart for the type of forceps deliveries in our cohort. Figures 2, 3 and 4 illustrate the distribution of age, BMI, and birth weight in our study population. Of the 1,492 women included in the study, 1,150 women (77 %) had sustained category 1 tears, 63 women (4 %) had sustained category 2 tears and 279 women (19 %) had sustained third-degree tears. The adjusted effect of each covariate on the relative risk (RR) ratio is interpreted given that the other variables in the model were held constant. The relative risk of third-/fourthdegree tears vs category 1 injury decreased by a factor of 0.96 (0.93–0.98) for every 1 year increase in the age, which was statistically significant (p=0.002). For every 5 - year increase in the women’s age, the RR of third-/fourth-degree tear vs category 1 injury decreased by a factor of 0.80 (0.70, 0.92), which was statistically significant (p=0.002). The relative risk ratio for third/fourth degree tears vs category 1 damage increased by a factor of 1.31 (1.14–1.52) with every 500-g increase in birth weight, which was statistically significant (p
