Invest Clin 63(3): 235 - 242, 2022 https://doi.org/10.54817/IC.v63n3a03

Corresponding author: Jie Li. Department of Obstetrics and Gynecology, Ningbo Women & Children’s Hospital,

Ningbo, China. E-mail: taomu36311039913@163.com

Analysis of high risk factors for

complications in the trial of vaginal delivery

due to uterine scarring in a subsequent

pregnancy to a cesarean section.

Ren Ye1, Weixia Wang2 and Jie Li1*

1Department of Obstetrics and Gynecology, Ningbo Women & Children’s Hospital,

Ningbo, China.

2Department of Obstetrics and Gynecology, Leling People’s Hospital, Dezhou, China.

Key words: scarred uterus; pregnancy; vaginal trial delivery; complications; high-risk

factors.

Abstract. The purpose of this work was to analyze the high-risk factors of com-

plications in the trial of vaginal delivery of a subsequent pregnancy for scar uterus

after a previous cesarean. 136 pregnant women with scar uterus with a history of

cesarean who were admitted to our obstetrics department from February 2016 to

March 2019 were selected and were divided into a successful group and a failed

group according to the results of pregnancy and trial of labor vaginal delivery. Gen-

eral data of before, during, and after delivery were collected and the high-risk fac-

tors for failed vaginal delivery of scar uterine were analyzed by the logistic regression

analysis. Among the 136 patients, 108 cases (79.41%) of vaginal trials were success-

ful, and 28 cases (20.59%) of vaginal trials faired. The univariate analysis showed

that the differences in gravidity, parity and the previous cesarean interval, vaginal

birth history, prenatal BMI, uterine contraction, gestational age, infant weight, dila-

tation of the cervix, cervical Bishop score, the height of the fetal head, the thickness

of the lower uterus, and whether the membranes were prematurely ruptured were

statistically significant (P<0.05). Logistic regression analysis showed vaginal birth

history, prenatal BMI ≥ 30 kg/m2, parity ≥ 2 times, cesarean interval <2 times,

dilatation of cervix ≥ 1 cm, the height of the fetal head ≥ -3, premature rupture

of the membrane and the thickness of the lower uterus of 3.0 to 3.9 cm were the

high-risk factors of complications in the vaginal trial delivery of pregnancy again for

scar uterus (P<0.05). It is feasible for pregnant women with scar uterus to undergo

vaginal delivery, but many related factors can affect the failure of trial of labor. It is

necessary to pay attention to all aspects of clinical examination and choose applica-

tions strictly according to the indications.

236 Ye et al.

Investigación Clínica 63(3): 2022

Análisis de factores de alto riesgo para complicaciones

en el trabajo de parto vaginal debidas a cicatrización uterina

en un embarazo posterior a una operación cesárea.

Invest Clin 2022; 63 (3): 235 – 242

Palabras clave: cicatriz uterina; embarazo; prueba de parto vaginal; complicaciones;

factores de alto riesgo.

Resumen. El propósito del presente trabajo fue analizar los factores de

alto riesgo de complicaciones por cicatriz uterina en la prueba de parto vagi-

nal del siguiente embarazo después de una cesárea previa. 136 gestantes con

cicatriz uterina fueron seleccionadas con antecedente de cesárea anterior que

ingresaron a nuestro servicio de obstetricia de febrero 2016 a marzo 2019, y

se dividieron en un grupo exitoso y un grupo fallido según los resultados de las

pruebas de embarazo y parto vaginal. Los datos generales anteriores fueron

recolectados, durante y después del parto y se analizaron los factores de alto

riesgo para el parto vaginal fallido de la cicatriz uterina mediante el análisis de

regresión logística. Entre las 136 pacientes, 108 casos (79,41%) de las pruebas

vaginales fueron exitosas y 28 casos (20,59%) de las pruebas vaginales fracasa-

ron. El análisis univariado mostró que las diferencias en la gravidez, la paridad

y el intervalo de cesárea previa, la historia de parto vaginal, el IMC prenatal,

la contracción uterina, la edad gestacional, el peso del lactante, la dilatación

del cuello uterino, la puntuación cervical de Bishop, la altura de la cabeza fe-

tal, el grosor del segmento uterino inferior, y si las membranas se habían roto

prematuramente fueron estadísticamente significativas (P<0,05). El análisis

de regresión logística mostró antecedente del parto vaginal, el IMC prenatal ≥

30 kg/m2, la paridad ≥ 2 veces, el intervalo entre cesáreas < 2 veces, la dila-

tación del cuello uterino ≥ 1 cm, la altura de la cabeza fetal ≥ -3, la ruptura

prematura de la membrana y el grosor del segmento uterino inferior de 3,0 a

3,9 cm fueron los factores de alto riesgo de complicaciones por cicatriz uterina

en la prueba de parto vaginal de un siguiente embarazo (P<0,05). Sería posi-

ble que las gestantes con cicatriz uterina vuelvan a someterse a parto vaginal,

pero existen muchos factores relacionados que inciden en el fracaso del trabajo

de parto. Es necesario prestar atención a todos los aspectos de la exploración

física y elegir las aplicaciones estrictamente de acuerdo con las indicaciones.

Received: 15-05-2022 Accepted: 16-07-2022

INTRODUCTION

A Cesarean section is an operation to

open the abdominal wall and uterus to re-

move the fetus that is an important opera-

tion in the field of obstetrics. It plays an im-

portant role in solving dystocia and severe

pregnancy complications; and reduces the

morbidity and mortality of mothers and in-

fants 1. At present, as the indications for ce-

sarean section surgery and the technology

of cesarean section become more and more

sophisticated, China’s cesarean section rate

has been above the global cesarean section

Complications in vaginal delivery due to uterine scarring after previous cesarean 237

Vol. 63(3): 235 - 242, 2022

warning line. Although cesarean section can

significantly reduce the incidence of dysto-

cia and postnatal adverse reactions, it can

significantly increase the number of preg-

nant women with scar uterus after cesarean

section, increase the risk of patients with

scar pregnancy, placental implantation, pla-

centa previa, and other events, which pose a

certain threat to the health of mothers and

infants 2-3. In recent years, with the full pop-

ularization of the national “second child”

policy, the number of women who have had

a vaginal delivery again after the cesarean

section has significantly increased. Related

data shows that 4, the risk of uterine rupture

during the vaginal delivery of pregnant wom-

en with scar uterus is obviously increased,

which easily leads to maternal and perinatal

death. Reviewing relevant research findings

at home and abroad 5, most of the referenc-

es mainly discuss the factors related to the

success of vaginal delivery in scar uterus re-

pregnancy. There are fewer factors related to

the complications of vaginal delivery in scar

uterus re-pregnancy, this study aims to ana-

lyze risk factors of complications in vaginal

trial delivery of a subsequent pregnancy for

scar uterus after cesarean section.

MATERIAL AND METHODS

Research subjects

136 pregnant women with scarred

uteri with a history of cesarean section

who were admitted to the obstetrics de-

partment of our hospital from February

2016 to March 2019 were selected as the

research subjects. This study was approved

by the ethics committee of our hospital.

Inclusion criteria: 1) those aged 22 to 40

years with 37 to 41 weeks gestation; 2) the

time between the last cesarean operation

and this pregnancy of all pregnant women

was more than 2 years; 3)the uterine scar

of the pregnant woman was located at the

lower section of the uterus; 4) the fetal po-

sition was normal and without absolute pel-

vic pelvis; 5) the pelvic bones of pregnant

women were normal; 6) the indication for

the last cesarean section operation did not

exist; 7) The patient and family members

were informed and signed a consent form.

Exclusion criteria: 1) those who had a his-

tory of two or more cesarean sections; 2)

patients with intrauterine multiple births

and non-term pregnancies; 3) patients with

previous history of uterine rupture; 4) preg-

nant women with uterine tumor disease; 5)

those who occur new cesarean section indi-

cations in this pregnancy; 6) those that had

placenta attachment or poor continuity of

muscle layer in the scar of the lower uterus.

7) products with estimated weights great-

er than 4000 grams were not considered.

136 pregnant women aged 22 to 40 years

old, with an average age of (27.82 ± 3.84)

years, 37 to 41 weeks of gestational age, an

average of (39.15 ± 1.07) weeks, with two

to five pregnancies, an average of (2.10 ±

1.03) times, and one to four times of parity,

with an average of (1.18 ± 0.47) times, and

the interval between cesarean sections was

24-168 months, with an average of (62.38

± 25.47) months. According to the results

of vaginal trial delivery, they were divided

into the successful group and failed groups.

Delivery methods

After admission, pregnant women un-

derwent detailed obstetric examinations

and fetal ultrasound examinations to evalu-

ate comprehensively their physical and preg-

nancy status. Pregnant women and their

families chose the delivery method based on

the actual situation. Continuous electronic

ECG monitoring was given, and the midwife

accompany the trial of pregnant women by

the way of one-on-one monitoring the prog-

ress of the labor process closely. After the

successful trial, it was checked whether the

uterus was complete and whether the uter-

ine scar had cracked. If the pregnant woman

does not give birth within 12 hours after

contraction, or if there are suspicious signs

of uterine rupture and fetal distress, a cesar-

ean section should be given immediately.

238 Ye et al.

Investigación Clínica 63(3): 2022

Data collection

The general information on prenatal,

perinatal, and postpartum for all pregnant

women was collected, including age, educa-

tion, pregnancy, parity, previous cesarean

sections interval, vaginal birth history, pre-

natal BMI, use of uterine contractions, gesta-

tional age, infant weight, admission uterine

dilation of the cervix, cervical Bishop score,

the height of the fetal head, lower uterine

segment thickness, premature rupture of

membranes, regular birth checkup, etc., and

the record content was checked.

Statistical methods

All the count data in this study are ex-

pressed in [n (%)]. The comparison between

the two groups was performed using the χ²

test. Logistic regression analysis was used

to analyze the high-risk factors for failed

vaginal delivery of scar uterine pregnancy.

P<0.05 was considered statistically signifi-

cant. The research data were analyzed using

the SPSS21.0 software package.

RESULTS

Analysis of maternal delivery results

Among the 136 patients, 108 cases

(79.41%) of successful vaginal trials were in

the successful group, 28 cases (20.59%) of

failed vaginal trials were in the failed group,

and the reasons for 28 cases of pregnant

women who failed vaginal trials and were

changed to cesarean section, are shown in

Table 1.

Table 1

Reasons for pregnant women who have failed

vaginal trials were changed to cesarean section.

Reasons Cases

Fetal distress 12 (42.86)

Secondary tocolytic weakness 1 (3.57)

Abnormal labor 7 (25.00)

Intrauterine infection 1 (3.57)

Other factors 7 (25.00)

Univariate analysis of factors related to

failed vaginal trial delivery of scar uterine

pregnancy

The univariate analysis showed that

there were statistically significant differences

in gravidity, parity, previous cesarean sections

interval, vaginal birth history, prenatal BMI,

use of uterine contraction, gestational age,

infant weight, admission dilation of the cer-

vix, cervical Bishop score, the height of the

fetal head, the thickness of the lower uterus,

and whether the membranes were premature-

ly ruptured (P <0.05). See Table 2.

Influencing factors and assignments

The high-risk factors and assignments

of failed vaginal trial delivery in scar uterine

pregnancy, are expressed in Table 3.

Logistic regression analysis of high-risk

factors for failed vaginal trial delivery

in scar uterus pregnancy

Taking the failed vaginal trial delivery

as the dependent variable, the statistically

significant indicators in Table 2 were used

as the dependent variables for evaluation

(see Table 3) and were included in the lo-

gistic regression analysis model. The results

showed that there was no history of vaginal

delivery, BMI ≥ 30 kg/m2, parity ≥ 2 times,

cesarean section interval < 2 times, admis-

sion dilation of cervix ≥ 1 cm, the height

of fetal head ≥ -3, premature rupture of

membranes, and 3.0-3.9cm of the thickness

of the lower uterus are high-risk factors for

complications in vaginal trial delivery in scar

uterus pregnancy (P <0.05) (see Table 4).

DISCUSSION

With the continuous increase in cesarean

section rate in the world and the widespread

application of laparoscopic myomectomy in

women of childbearing age, the problem of

subsequent pregnancies for scarred uterus is

inevitable 6. With the gradual increase in cesar-

ean section rate, the scarred uterus appears in

large numbers. There are two methods of deliv-

Complications in vaginal delivery due to uterine scarring after previous cesarean 239

Vol. 63(3): 235 - 242, 2022

Table 2

Univariate analysis of factors related to failed vaginal delivery of scar uterine pregnancy.

Relative factors Successful group

(n=108) (%)*

Failed group

(n=28) (%)* F p-value**

Age <35 years 99(91.67) 27(96.43) 0.740 0.390

≥35 years 9(8.33) 1(3.57)

Education Under the high school 85(78.70) 21(75.00) 0.177 0.674

High school or above 23(21.30) 7(25.00)

Gravidity <3 times 33(30.56) 12(42.56) 1.520 0.218

≥3 times 75(69.44) 16(57.14)

Parity <2 times 83(76.85) 27(96.43) 5.511 0.019

≥2 times 25(23.15) 1(3.57)

Previous cesarean

sections interval

24~36 months 55(50.93) 21(75.00) 5.227 0.022

>36 months 53(49.07) 7(25.00)

Vaginal birth history Yes 67(62.04) 3(10.71) 11.825 0.001

No 41(37.96) 25(89.29)

Prenatal BMI <30 kg/m2 78(72.22) 14(50.00) 5.017 0.025

≥30 kg/m2 30(27.78) 14(50.00)

Use of uterine contraction Yes 55(50.93) 8(28.57) 7.281 0.007

No 53(49.07) 20(71.43)

Gestational age <40 weeks 82(75.93) 16(57.14) 3.896 0.048

≥40 weeks 26(24.07) 12(42.56)

Infant weight <3.5kg 72(66.67) 12(42.56) 5.338 0.021

≥3.5kg 36(33.33) 16(57.14)

Dilation of cervix <1cm 44(40.74) 22(78.57) 12.740 <0.001

≥1cm 64(59.26) 6(21.43)

Cervical Bishop score <3 scores 4(3.70) 4(14.29) 4.497 0.034

≥3 scores 104(96.30) 24(85.71)

Height of the fetal head <-3 4(3.70) 4(14.29) 4.497 0.034

≥-3 104(96.30) 24(85.71)

The thickness of the lower

uterus

3.0~3.9cm 32(29.63) 16(57.14) 7.370 0.007

≥4.0cm 76(70.37) 12(42.56)

Whether the membranes

were prematurely ruptured

Yes 16(14.81) 10(35.71) 6.281 0.012

No 92(85.19) 18(64.29)

Regular birth checkup Yes 75(69.44) 16(57.14) 1.520 0.218

No 33(30.56) 12(42.86)

* n= number, % (percent).

**P-value based on univariate analysis (linear regression).

240 Ye et al.

Investigación Clínica 63(3): 2022

Table 3

High-risk factors and assignments of failed vaginal trial delivery in scar uterine pregnancy.

Code Variate Assignments

X1 Gender 1=male, 2=female

X2 Education 1= under the high school, 2= high school or above

X3 Gravidity 1=<3 times, 2=≥3 times

X4 Parity 1=<2 times, 2=≥2 times

X5 Previous cesarean sections interval 1=24~36 months, 2>36 months

X6 Vaginal birth history 1=yes, 2=no

X7 Prenatal BMI 1=<30 kg/m2, 2=≥30 kg/m2

X8* Use of uterine contraction 1=yes, 2=no

X9 Gestational age 1=<40 weeks, 2=≥40 weeks

X10** Infant weight 1=<3.5kg, 2=≥3.5kg

X11 Dilation of cervix 1=<1cm, 2=≥1cm

X12 Cervical Bishop score 1=<3 scores, 2=≥3 scores

X13 Height of the fetal head 1=<-3, 2=≥-3

X14 The thickness of the lower uterus 1=3.0~3.9cm, 2=≥4.0cm

X15 Whether the membranes were

prematurely ruptured

1=yes, 2=no

X16 Regular birth checkup 1=yes, 2=no

Y Vaginal trial delivery results 1=successful, 2=failed

* Oxytocic medications were used.

** The cut-off point of 3500 grams was taken intentionally.

Table 4

Logistic regression analysis of high-risk factors for failed vaginal delivery of scar uterine pregnancy.

Influencing factors βSE Wald p OR 95%CI

No history of vaginal delivery 0.839 0.175 20.135 0.001 2.319 1.614~3.253

Prenatal BMI≥30 kg/m2 0.078 0.021 19.561 0.001 1.120 1.041~1.132

Parity≥2 times 0.737 0.245 8.426 0.002 2.142 1.031~4.173

Cesarean section interval

<2 times

0.086

0.021

4.167

0.012

1.169

1.022~2.637

dilation of cervix≥1cm 0.026 0.017 4.865 0.014 1.038 1.004~1.071

height of fetal head≥-3 0.802 0.232 11.028 0.001 2.146 1.210~4.281

premature rupture

of membranes

0.364

0.175

4.010

0.039

1.337

1.002~2.112

3.0-3.9cm of the thickness

of the lower uterus

0.428

0.125

5.814

0.014

1.546

1.027~2.587

Complications in vaginal delivery due to uterine scarring after previous cesarean 241

Vol. 63(3): 235 - 242, 2022

eries for scarred uterus in subsequent pregnan-

cies, including cesarean section and vaginal

delivery. A second cesarean section can reduce

certain maternal and infant complications and

newborn death rates, but it can increase the

incidence of pain, pelvic adhesions, and surgi-

cal injuries in patients. The guided delivery in

a subsequent pregnancy for scarred uterus is

more economical than a second cesarean deliv-

ery, with less postpartum pain, and can reduce

placental implantation and risk of placenta

placement 7-8. In recent years, the concept of

vaginal trial delivery of a subsequent pregnan-

cy for scarred uterus after the cesarean sec-

tion has been accepted by obstetricians. Some

scholars have found that the success rate of

vaginal delivery after scar uterus for a previous

cesarean section can reach 82.61%. However,

there is currently no clear assessment of risk

factors for vaginal trials in China, and most

pregnant women have a certain degree of re-

jection of vaginal trials 9-10. The results of this

study showed that in 136 patients, 108 cases

of vaginal trials were successful (79.41%), and

28 cases of vaginal trials failed (20.59%), which

suggested that the scarred uterus has certain

feasibility. The associated risk factors for preg-

nant women who have failed delivery were ana-

lyzed in this study.

Logistic regression analysis showed no

history of vaginal birth, prenatal BMI ≥ 30

kg/m2, parity ≥ 2 times, cesarean delivery

interval <2 times, admission dilation of

cervix≥ 1 cm, the height of fetal head ≥-

3, premature rupture of membranes and a

thickness of 3.0 - 3.9cm at the lower uterus

are the high-risk factors for complications in

the vaginal trial of scar uterine pregnancy (P

<0.05). Increased prenatal BMI can increase

the risk of adverse pregnancy outcomes such

as hypertension and diabetes during preg-

nancy. Some scholars have found that preg-

nant women with high prenatal BMI values

have a relatively slow expansion of the cer-

vix during vaginal delivery, increasing the

risk of vaginal trial failure 11. Relevant data

show that the shorter the interval from the

last cesarean section, the higher the risk of

uterine rupture in pregnant women 12. First

fetal head exposure refers to the part of the

fetus that first enters the pelvic entrance.

Pregnant women with high first fetal head

exposure have a higher incidence of dysto-

cia 13. Premature rupture of membranes is

a common perinatal complication, which

refers to the natural rupture of membranes

before labor, which can lead to an increase

in perinatal mortality. Relevant data 14 show

that the incidence of neonatal asphyxia after

cesarean delivery in pregnant women with

fetal head height and premature rupture of

membranes has significantly increased. The

thickness of the lower part of the uterus is

a predictive indicator of uterine threatened

rupture. When the thickness of the lower

part of the uterus is low, it can increase the

scar tension during labor and prone to com-

plications such as uterine rupture 15.

In summary, no history of vaginal birth,

prenatal BMI ≥ 30 kg/m2, parity ≥ 2 times,

cesarean section interval <2 times, admis-

sion dilation of cervix≥ 1 cm, the height

of fetal head ≥- 3, premature rupture of

membranes and a thickness of 3.0 - 3.9 cm

at the lower uterus are the high-risk factors

for complications in the vaginal trial of scar

uterine pregnancy. Therefore, a vaginal trial

for pregnant women with a scarred uterus

is feasible. However, there are many relevant

factors affecting the failure of trial of labor,

and more attention should be paid to all as-

pects of inspection, and choose the applica-

tion strictly according to the indication.

Authors’ Contribution

• Ren Ye and Weixia Wang collected the

samples.

• Ren Ye and Weixia Wang analyzed the

data.

• Ren Ye and Jie Li conducted the ex-

periments and analyzed the results.

All authors discussed the results and

wrote the manuscript.

242 Ye et al.

Investigación Clínica 63(3): 2022

Funding

The research was supported by: Ning-

bo key discipline women’s health care (No.

2022-f27).

Conflict of interests

The authors declare no conflict of in-

terests.

Author’s ORCID numbers

• Ren Ye: 0000-0002-8366-8596

• Weixia Wang: 0000-0002-5658-8961

• Jie Li: 0000-0001-6629-7319

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