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ORIGINAL RESEARCH
Association Between Second-Trimester
Cervical Length and Cesarean Delivery
in Multiparas
Emily S. Miller, MD, MPH, Brett Einerson, MD, MPH, Sadia Sahabi, BA, William A. Grobman, MD, MBA
Objectives—The purpose of this study was to determine whether there is an association
between second-trimester cervical length and cesarean delivery in women with a prior
vaginal delivery.
Methods—We conducted a retrospective cohort study of multiparous women with singleton gestations who underwent routine cervical length screening between 18 and 24
weeks’ gestation and labored after 34 weeks. Cervical lengths were divided into quartiles,
and the frequency of cesarean delivery was compared across the groups. Indications for
cesarean delivery were also compared. A multivariable logistic regression was performed
with cervical length as a categorical and a continuous variable to adjust for potential
confounders.
Results—Of the 2260 multiparas who met inclusion criteria, 63 (2.8%) underwent a
cesarean delivery. We observed no association between the second-trimester cervical
length quartile and the frequency of cesarean delivery (2.1%, 3.5%, 2.3%, and 3.1%,
respectively; P = .434). Further analysis using cervical length as a continuous variable
and controlling for potential confounding variables did not change this result (adjusted
odds ratio, 1.08; 95% confidence interval, 0.80–1.46).
Conclusions—The second-trimester cervical length quartile in multiparas is not associated with an increased frequency of cesarean delivery. This finding differs from studies
of nulliparas.
Key Words—cervical length; cesarean delivery; obstetrics; obstetric ultrasound; transvaginal sonograph
Received December 6, 2013, from Northwestern
University, Feinberg School of Medicine, Chicago,
Illinois USA. Revision requested January 20,
2014. Revised manuscript accepted for publication
January 31, 2014.
Address correspondence to Emily S. Miller,
MD, MPH, Northwestern University, Feinberg
School of Medicine, 250 E Superior St, Suite 052185, Chicago, IL 60611 USA.
E-mail: [email protected].
edu
Abbreviations
BMI, body mass index; CI, confidence interval; OR, odds ratio
doi:10.7863/ultra.33.10.1733
T
he cervix plays a pivotal role in regulating the timing and
successful completion of labor. Histologically, remodeling
and conditioning of the cervix begin long before the initiation of labor.1 Correspondingly, the cervix begins a process of progressive shortening, which is demonstrable by sonography in the
second trimester.2 The consequences of a short cervical length are
clear: women with a short cervix in the second trimester have an
increased risk of preterm delivery.3–7
Since a short cervical length is associated with early labor, the
converse might be true that a long cervical length is associated with
ineffective preparation for labor. Indeed, a long cervical length near
the end of pregnancy is associated with a higher likelihood of induction and cesarean delivery.8 Women with longer cervical lengths in
the second trimester also may be at risk for cesarean delivery due to
an increased chance of arrest disorders. One study of nulliparous
women in the United Kingdom showed an association between a
©2014 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2014; 33:1733–1736 | 0278-4297 | www.aium.org
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Miller et al—Second-Trimester Cervical Length and Cesarean Delivery in Multiparas
longer cervical length in the second trimester and subsequent cesarean delivery.9 A subsequent investigation in
the United States confirmed this relationship and found the
increase in risk to be predominantly related to the increased
risk of arrest of dilatation.10
However, multiparas are considerably less likely than
nulliparas to require a cesarean delivery or to have an arrest
disorder. Whether an association between second-trimester
cervical changes and cesarean delivery also is present in
multiparas is unknown. We hypothesized that, as in nulliparous women, multiparous women with a longer cervical
length would have an increased frequency of cesarean
delivery for labor arrest. Our objective, therefore, was to
study, among women with a prior vaginal delivery and no
prior cesarean delivery, whether cervical length measured
during routine second-trimester screening is associated
with the risk of cesarean delivery specifically in multiparas.
Materials and Methods
We conducted a cohort study of women who received routine cervical length screening between December 2010
and January 2012. The Institutional Review Board of
Northwestern University approved this study. Women
were included in this analysis if they were older than 18
years, had a singleton gestation, attempted a vaginal delivery, and delivered at or after 34 weeks’ gestation. Women
who underwent a termination of pregnancy or had a fetal
demise were excluded.
During the study period at the institution where the
study occurred, transvaginal cervical length assessment
between 18 and 24 weeks’ gestation was considered a
routine part of the anatomic survey. Cervical length was
measured transvaginally by staff sonographers and verified
by a sonologist, all of whom were previously trained according to the method of Iams et al.4 Records of all women who
had a second-trimester cervical length measurement were
identified by a query of the clinical sonographic reports.
If multiple measurements were taken, the measurement
taken closest to 20 weeks’ gestation was used.
Once women with second-trimester transvaginal cervical length measurements were identified, their medical
charts were reviewed to identify whether they met inclusion
criteria. The charts of those eligible were then abstracted for
demographic and obstetric characteristics, including
maternal age, race/ethnicity, tobacco use, body mass index
(BMI) at delivery, prior cervical excision procedures (eg,
cold knife cone and loop electrosurgical excision procedures), method of conception, and pregnancy complications (eg, hypertensive disorders, diabetes or gestational
1734
diabetes, and oligohydramnios). The gestational age at
delivery, type of labor (ie, induced or spontaneous), and
birth weight in the index pregnancy also were abstracted.
Cervical length was divided into quartiles to facilitate
analysis. Baseline patient and obstetric characteristics of
the study population were compared according to these
quartiles. Comparisons were performed by the KruskalWallis test or χ2 analysis for continuous and categorical
variables, respectively, and the nonparametric test for trend
was used to assess trends of categorical variables. The primary outcome was cesarean delivery, which was compared
according to the cervical length quartile. In addition, the
indication for cesarean delivery, dichotomized as either an
arrest disorder or “other” indication, was compared by
cervical length quartile.
Multivariable logistic regression was performed to
determine whether cervical length (both as a categorical
and a continuous variable) was independently associated
with cesarean delivery. Variables were entered into a multivariable model if they showed an association with the cervical length quartile at a P < .1 level in the bivariable analysis.
Odds ratios (ORs) and 95% confidence intervals (CIs)
were estimated. All tests were 2 tailed, and P < .05 was used
to define statistical significance. Analyses were performed
with Stata version 11.1 software (StataCorp, College
Station, TX).
Results
During the study period, 2260 multiparas met inclusion
criteria. Of these, 63 (2.8%) underwent a cesarean delivery.
The indications for cesarean delivery were a nonreassuring
fetal status in 23 women (36.5%) and an arrest disorder in
40 (63.5%).
Baseline demographic and clinical characteristics of
the study population, stratified by cervical length quartile,
are shown in Table 1. Compared to those in the lowest
quartile, women with longer cervical lengths were more
likely to be Hispanic and have a larger BMI. Women in the
higher quartiles also were less likely to have undergone a
prior cervical excision procedure. Finally, women with
longer cervical lengths were more likely to deliver later and
have higher neonatal birth weights.
There was no significant relationship between cesarean
delivery and the cervical length quartile (Table 2). When
separated by indications for cesarean delivery, cervical
length was not associated with the risk of cesarean delivery,
even among the subset with cesarean delivery for arrest disorders. Results were similar when the nonparametric test
for trend was used. Adjusting for potential confounders in
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Miller et al—Second-Trimester Cervical Length and Cesarean Delivery in Multiparas
a multivariable logistic regression did not change this conclusion (Table 3). Similarly, when cervical length was
entered into the regression as a continuous variable, there
was no identified association between cervical length and
the odds of cesarean delivery (adjusted OR, 1.08; 95% confidence interval, 0.80–1.46).
To the best of our knowledge, this study is the first to
investigate the relationship between cervical length and
cesarean delivery in multiparous patients. The results are in
contrast to previous studies of nulliparous patients. Smith
et al9 first reported an association between the secondtrimester cervical length quartile and frequency of cesarean
delivery in a large population of nulliparous women in the
United Kingdom.9 A study from the United States confirmed these findings in a general population of nulliparous
women undergoing routine cervical length screening.10
In both of these studies, the authors found a trend between
an increasing second-trimester cervical length quartile and
cesarean delivery. Both studies also found increased ORs
for cesarean delivery among women in the fourth quartile
Discussion
In this study of multiparas with a prior vaginal delivery, we
observed no association between second-trimester cervical
length and cesarean delivery. The absence of an association existed for cesarean delivery in general as well as for
cesarean delivery due to an arrest disorder.
Table 1. Patient Characteristics Stratified by Cervical Length Quartile
Characteristic
1st Quartile
(n = 561)
Cervical length, cm
3.6 (3.3–3.8)
Gestational age at cervical length, wk 20.3 (19.9–20.7)
Maternal age, y
33 (30–35)
Race
White
291 (58.1)
Black
68 (13.6)
Hispanic
112 (22.4)
Other
30 (6.0)
Smoked during pregnancy
13 (2.4)
BMI at delivery
28.4 (25.9–32.3)
Prior cervical excision procedure
63 (11.2)
Method of conception
In vitro fertilization
9 (1.8)
Any ART
10 (1.9)
Pregnancy complications
Hypertensive disorder
28 (5.0)
GDM or DM
35 (6.2)
Oligohydramnios
12 (2.1)
Gestational age at delivery, wk
39.1 (38.4–39.7)
≥39
357 (63.6)
≥41
16 (2.9)
Induction of labor
228 (40.6)
Birth weight, g
3380 (3075–3650)
2nd Quartile
(n = 598)
3rd Quartile
(n = 560)
4th Quartile
(n = 540)
4.3 (4.1–4.4)
20.3 (19.9–20.7)
33 (29–36)
4.8 (4.7–4.9)
20.3 (19.9–20.7)
33 (29–36)
5.6 (5.3–6.1)
20.1 (19.9–20.7)
33 (29–36)
309 (56.6)
53 (9.7)
150 (27.5)
34 (6.2)
5 (0.9)
28.8 (26.1–32.4)
37 (6.1)
306 (59.0)
52 (10.0)
145 (27.9)
16 (3.1)
7 (1.3)
29.5 (26.6–33.0)
41 (7.3)
250 (51.1)
46 (9.4)
165 (33.7)
28 (5.7)
6 (1.2)
29.5 (26.9–33.7)
19 (3.5)
.159
<.001
<.001
11 (2.0)
12 (2.2)
14 (2.7)
18 (3.5)
15 (3.0)
17 (3.4)
.488
.272
25 (4.2)
39 (6.5)
18 (3.0)
39.3 (38.7–39.9)
411 (68.7)
31 (5.2)
238 (39.8)
3425 (3130–3715)
31 (5.5)
38 (6.8)
11 (2.0)
39.3 (38.9–40.0)
409 (73.0)
28 (5.0)
225 (40.2)
3450 (3175–3760)
18 (3.3)
36 (6.7)
7 (1.3)
39.3 (38.6–40.0)
371 (68.7)
31 (5.7)
188 (34.8)
3465 (3158–3775)
.314
.985
.250
<.001
.009
.111
.165
.002
P
<.001
.095
.764
.002
Data are presented as mean (range) and number (percent). ART indicates assisted reproductive technology; DM, diabetes mellitus; and GDM,
gestational diabetes mellitus.
Table 2. Frequency of and Indications for Cesarean Delivery Stratified by Cervical Length Quartile
Parameter
Cesarean delivery
Indication
Arrest disorder
Other
1st Quartile
2nd Quartile
3rd Quartile
4th Quartile
P
12 (2.1)
21 (3.5)
13 (2.3)
17 (3.1)
.434
7 (1.2)
5 (0.9)
12 (2.0)
9 (1.5)
8 (1.4)
5 (0.9)
13 (2.4)
4 (0.7)
.439
.573
Data are presented as number (percent).
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Miller et al—Second-Trimester Cervical Length and Cesarean Delivery in Multiparas
compared to women in the first quartile, adjusted for
possible confounding factors (adjusted ORs, 1.68 and 1.77,
respectively). The same trend was not identified in this
population of multiparas.
As anticipated, the rate of cesarean delivery in this
group of multiparous women was low; more than 97% of
all women in this study achieved a vaginal delivery. Thus,
it is possible that the absence of an association between
second-trimester cervical length and cesarean delivery was
the consequence of inadequate statistical power. Despite a
large sample of multiparas, the total number of cesarean
deliveries was only 63 (2.8% of all deliveries). However,
with our sample size and the baseline cesarean rate in this
study population, we were powered to detect a 2.5-fold
increase in the cesarean frequency between the highest and
lowest quartiles. Also, there was no evidence of a trend by
quartile in this study. If a true association between cervical
length and cesarean delivery existed in multiparas, we
would expect to see a “dose-response” trend, even if pairwise comparisons were not statistically significant.
This study offers further insight into the importance
of second-trimester cervical length in predicting the risk of
parturition abnormalities. Mounting evidence suggests
that a longer cervical length in nulliparas is predictive of
labor arrest and cesarean delivery.9,10 Changes in the cervix
well before the onset of labor, it seems, must play an
important role in preparation for successful parturition.
This study suggests that the same association between cervical length and cesarean delivery does not exist in multiparas, implying perhaps that cervical changes required for
successful labor occur at a different time, or in a different
unmeasured manner, in the pregnancies of multiparas.
References
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Table 3. Multivariable Analyses of Factors Associated With Cesarean
Delivery
Parameter
Cervical length quartile
1st (referent)
2nd
3rd
4th
Race
White (referent)
Black
Hispanic
Other
Prior cervical excision procedure
BMI
Gestational age at delivery
1736
Adjusted OR
95% CI
1.00
1.48
0.98
1.32
0.69–3.17
0.42–2.25
0.60–2.90
1.00
1.62
1.52
1.70
0.57
1.02
1.20
0.69–3.80
0.82–2.85
0.58–5.01
0.14–2.40
0.97–1.07
0.95–1.52
J Ultrasound Med 2014; 33:1733–1736