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INTRODUCTION
A Cesarean section is an operation to open the abdominal wall and uterus to remove the fetus that is an important operation in the field of obstetrics. It plays an important role in solving dystocia and severe pregnancy complications; and reduces the morbidity and mortality of mothers and infants 1. At present, as the indications for cesarean 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 warning line. Although cesarean section can significantly reduce the incidence of dystocia and postnatal adverse reactions, it can significantly increase the number of pregnant women with scar uterus after cesarean section, increase the risk of patients with scar pregnancy, placental implantation, placenta previa, and other events, which pose a certain threat to the health of mothers and infants 2-3. In recent years, with the full popularization 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 women 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 references mainly discuss the factors related to the success of vaginal delivery in scar uterus repregnancy. There are fewer factors related to the complications of vaginal delivery in scar uterus re-pregnancy, this study aims to analyze 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 department 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 position was normal and without absolute pelvic 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 history 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) pregnant women with uterine tumor disease; 5) those who occur new cesarean section indications 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 greater 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 underwent detailed obstetric examinations and fetal ultrasound examinations to evaluate comprehensively their physical and pregnancy 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 progress of the labor process closely. After the successful trial, it was checked whether the uterus was complete and whether the uterine 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 cesarean section should be given immediately.
Data collection
The general information on prenatal, perinatal, and postpartum for all pregnant women was collected, including age, education, pregnancy, parity, previous cesarean sections interval, vaginal birth history, prenatal BMI, use of uterine contractions, gestational 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 expressed 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 significant. 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.
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 cervix, cervical Bishop score, the height of the fetal head, the thickness of the lower uterus, and whether the membranes were prematurely ruptured (P <0.05). See Table 2.
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).
Influencing factors and assignments
The high-risk factors and assignments of failed vaginal trial delivery in scar uterine pregnancy, are expressed in Table 3.
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.
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 logistic 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, admission 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).
Table 4 Logistic regression analysis of high-risk factors for failed vaginal delivery of scar uterine pregnancy.
| Influencing factors | β | SE | 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 |
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 cesarean section rate, the scarred uterus appears in large numbers. There are two methods of deliveries for scarred uterus in subsequent pregnancies, 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 surgical injuries in patients. The guided delivery in a subsequent pregnancy for scarred uterus is more economical than a second cesarean delivery, 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 pregnancy for scarred uterus after the cesarean section 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 rejection 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 pregnant women who have failed delivery were analyzed 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 pregnancy. Some scholars have found that pregnant women with high prenatal BMI values have a relatively slow expansion of the cervix 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 dystocia 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 complications 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, admission 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 aspects of inspection, and choose the application strictly according to the indication.
