Authors

Sample Size/ Characteristics considering only vaginal births

Method of LA assessment

Reported LA tear rate % (n)

Predictors of Any LevatorAni Muscle Tear

Maternal age

Instrumental delivery

Anal sphincter laceration

Prolonged second stage

Episiotomy

Infant Size

Infant head circumference

Kearney et al. 2006

N = 160 Case control with cases incontinent and controls continent recruited 9 - 12 months post birth between 1997 - 2001 (USA)

MRI

18.1%

(29 of 160)

p = 0.001 mean age = 32.8 vs 29.3 years for those with and without LA tear respectively

VacuumNS forceps OR = 14.7

OR = 8.1

mean = 92.5 min (no injury) mean = 170.5 min (LA injury)

(p = 0.001)

3.1 OR

NS

not reported

Dietz & Lanzarone 2005

N = 39 All comers recruited prospective to birth (Austria)

3D trans- labial ultra- sound

36%

(14 of 39)

mean age = 31.6 NS

(p = 0.10)

p = 0.07

Factors not specifically identified but reported as not significant

Valsky et al. 2009

N = 210 All comers recruited 23 - 72 hours post birth between 2006 - 2008

(Jerusalem)

3D trans- perineal ultra sound

18.6%

(39 of 210)

Mean age = 25.8 ± 4.3 NS

(p = 0.104)

VacuumNS

not reported

mean = 69.01 (no injury) mean = 87.0 min (LA injury) OR = 2.27 p = 0.027

NS

mean = 3128 gm (no injury)

mean = 3309.41 gm (LA injury)

p = 0.024

mean = 33.77 cm (no injury)

mean = 34.24 cm (LA injury) OR = 3.343 p = 0.040

Shek & Dietz 2010

N = 240 All comers recruited prospective to birth 2005-2008. Post birth dates study measures varied. (Australia)

4D trans- labial ultra- sound

13%

(32 of 240)

Mean age = 25.9 significance not reported

Forceps OR = 4.2 vacuum NS

not reported

NS

OR = 2.34

NS

NS

Cassadó Garriga et al.

2011

N = 120 Case Control with cases (n = 60) forceps delivery and controls (n = 60) vaginal birth without episiotomy or perineal tears studied 40 to 120 days post birth (Spain)

4D introital ultra- sound

61.7%

(37 of 60)

cases 13.3% (8 of 60)

controls

Mean age = 30.2 ± 3.6 vs 29.4 ± 4.1 for cases and controls respectively. significance not reported

Forceps OR 10.47 (CI 4.2 - 25.9)

not reported

not reported

not reported

NS

not reported

Chan et al.

2012

N = 263 All comers recruited prospective to birth, 2009 - 2010, studied 8 weeks postpartum

(Hong Kong)

3D trans- labial ultra- sound

71.4%

(10 of 14)- forceps 33.3%

(16 of 48)- vacuum 15.4%

(31 of 201)- spontaneous vaginal birth

mean age 30.6 ± 3.9 NS

(p = 0.82)

Forceps p < 0.001 Vacuum p < 0.001 any operative vaginal delivery Significance remained in multivariate analysis OR 3.09 (CI 1.46 - 6.52)

not reported

p = 0.05 in multivariate analysis p < 0.001 in univariate analysis.

All but 10 women in the sample had episiotomies, so lack of varianceprohibited analysis of independent contribution

NS

(p = 0.47) in multivariate analysis p = 0.04 in univariate analysis

not included in multivariate analysis, substantial amount of missing data

p = 0.01 in univariate analysis