Baylor University Medical Center Proceedings April 2017 - 152

Table 1. Noncategorical characteristics of the 127 primigravid
study participants
Characteristic

Table 2. Categorical characteristics of the 127 primigravid study
participants

Mean (SD)

Range

Characteristic

Perineal body measurement (cm)

3.7 (0.5)

2.3-5.0

Race

Age (years)

23.7 (4.7)

15-38

Gestational age (weeks)

39.6 (1.1)

37.1-41.3

Body mass index (kg/m2)*

31.2 (5.9)

20.8-50.3

Baby weight (g)

3367 (403) 2156-4460

White
African American
Hispanic
Asian
Native American
Other

83 (65%)
19 (15%)
19 (15%)
3 (2%)
1 (1%)
2 (1%)

Presentations

Occiput anterior
Left occiput anterior
Right occiput anterior
Occiput transverse

97 (76%)
17 (13%)
11 (8%)
2 (1%)

Lacerations

None
First degree
Second degree
Third degree
Fourth degree

38 (29%)
17 (13%)
67 (52%)
3 (2%)
2 (1%)

Episiotomy

None
Midline

125 (98%)
2 (2%)

Delivery type

Spontaneous vaginal
Vacuum assisted
Forceps

107 (84%)
10 (8%)
10 (8%)

Oxytocin used

Yes
No
Missing data

106 (83%)
20 (16%)
1 (1%)

Length of second stage (min)

58 (44)

5-232

*Data were missing for three patients.

Cases were partitioned into two categories of lacerations-1)
none to second degree and 2) third or fourth degree-with variables presented as means with standard deviations or percentages. The data were analyzed using univariate analyses (Student's
t test or chi-square test) for differences. Receiver-operator curve
analyses were performed on parametric variables to identify
thresholds and statistical differences associated with third- and
fourth-degree lacerations. Variables with trends (P < 0.1) were
formatted as logistical for evaluation using a multiple logistic
regression model to identify those with significant associations
with increased severity of vaginal lacerations. The final model
included variables with P < 0.05.
RESULTS
Data were collected on 127 women from December 2011
through March 2013. Eighty-nine percent of the measurements
were obtained by two physicians. Tables 1 and 2 list the parametric and nonparametric variables. The mean perineal body
length among these primigravid women averaged 3.7 cm, with
a range of 2.3 to 5.0. Among this group of women, the rate of
third- and fourth-degree lacerations was 3.9% (5/127).
The relation of patient characteristics to the two subgroups
of lacerations is shown in Table 3 with results of univariate analyses. A tendency was seen with patient age and perineal body
length (P ≤ 0.1) being related to variation in laceration degree.
The duration of second stage of labor and operative vaginal
delivery were significant in relation to variation in laceration
degree (P ≤ 0.05). Receiver-operator curve analysis was used
to set thresholds for age, perineal body length, and duration
of second stage of labor, and a logistic regression model was
used to identify independent associations from among these
four variables, using the threshold values (Table 4). Both the
duration of second stage of labor and perineal body length were
found to have significant (P < 0.04) independent associations
with third- and fourth-degree lacerations. The odds ratio for
the duration of second stage >99 minutes was 32 (1.3 to 807,
95% CI). The odds ratio for perineal body length ≤3.5 cm was
24 (1.3 to 456).
DISCUSSION
This is the first prospective trial to address the association
of perineal body length with the risk of third- and fourth152

Categories

n (%)

 

degree lacerations in primigravid women in an institution
with a low episiotomy rate. Our finding in univariate analysis
that the length of the second stage of labor and having had an
operative delivery were risk factors for third- or fourth-degree
laceration corroborated many prior studies. However, using
logistic regression analysis, we found that a perineal body
length of ≤3.5 cm and a second stage of labor >99 minutes
were the most predictive for risk of third- and fourth-degree
lacerations.
Several studies have addressed perineal body length as a
possible risk factor for severe perineal body lacerations during vaginal delivery (10-14). These studies differ from ours.
They all had episiotomy rates much greater than our rate of
<2%. The study by Deering, which more closely matched
our patient population, was retrospective in nature and included both multiparous and primiparous patients. In another
American study, most patients were of Asian descent (14).
However, our average perineal body length of 3.7 cm was
consistent with the average perineal body reported in other
Western studies (12-15). A recent study by Tsai et al failed to
show a relationship between perineal body length and severe
lacerations; however, this study had a larger operative vaginal
delivery rate, a higher episiotomy rate, and a higher number
of occiput posterior deliveries, which may have made reasons
for severe lacerations less clear (14).

Baylor University Medical Center Proceedings

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