Cervical Length and Posterior Cervical Angle measured by Transvaginal US as Alternative to Bishop Score in Prediction of Successful Labor Induction

INTRODUCTION

Softening, ripening, dilatation, and repair are the four phases of connective tissue modification in the cervix during gestation. Despite their proximity in time, each step is governed in its own way.

labor induction is a frequent and necessary part of modern obstetric treatment, with roughly 20% of pregnancies requiring it. ¹

Immediate problems such as ruptured membranes with chorioamnionitis or severe Pre-eclampsia are indications. Some of the more common reasons include membrane rupture without labor, gestational high blood pressure, non-reassuring fetal condition, post-term pregnancy, and other maternal medical illnesses such as persistent high blood pressure and diabetes. ²

Transvaginal sonographic Ultrasound of the cervix may give a more accurate predictor of effective induction than the Bishop Score, according to several recent research. Hatfield and colleagues (2007) conducted a meta-analysis of 20 studies in which transvaginal ultrasonography (TVUS) was used to

determine cervical length and predict effective induction of labor. The authors found that the subject still remained unsolved due to the diversity of research criteria.

Uterine hyper stimulation, unsuccessful induction, umbilical cord prolapses, and uterine rupture are among risks associated with induction of labor. The conventional method of establishing whether an initiated labor will result in a successful vaginal delivery is to digitally check the cervix. Bishop's scoring system, published in 1964, is the most frequently recognized and utilized. A Bishop Score of (9) indicates a high possibility of induction success. A Bishop Score of four or fewer indicates an unfavorable cervix and may signal cervical ripening. ³

However, the Bishop Score's assessment of the cervix's 'favorability' before to induction is very subjective, and multiple studies have shown that it has a poor prognosis for induction success, especially in women with a poor Bishop Score. ⁴

The supra-vaginal part of the cervix accounts for roughly half of the cervical length, and its length varies from woman to woman. It's tough to digitally assess this part of the cervix.

Cervical length and posterior cervical angle measurement through transvaginal ultrasonography, on the other hand, may be a more objective method of detecting cervical status. ⁵

The study's goal was to figure out what qualities a candidate should have in order to have a successful induction of labor.

PATIENTS AND METHODS

This was a prospective randomized study, where 100 pregnant women not in labor indicated for termination of pregnancy, The study was admitted to recruit one hundred (100) women all are primigravidas between 37:42 weeks, patients to whom induction of labour at the casualty of (El Galaa Teaching Maternity Hospital, Al Hussein University Hospital, Cairo, Egypt), between August 2020 and June, 2021.

All patients were subjected to the following:

Data recording include: Maternal age, gestational age at induction, maternal medical disorder if present, indication for induction of labor: Prolonged pregnancy, medical disorder e.g. gestational diabetes and hypertension, bishop Score before induction, cervical length(mm) and Posterior cervical angle before induction, induction delivery time, maternal and neonatal morbidity, percentage of women deliver by Prostaglandins only, percentage of women require oxytocin, mode of delivery (Vaginal or Cesarean Section) and baby weight and Apgar score at first minute after birth.

Inclusion criteria: Singleton Pregnant with cephalic presentation, primigravida, 37:42 weeks gestational age, no prior uterine surgical operations, baby weight 4 kg, and no liquor anomalies.

Exclusion criteria: Non-Vertex presentation, previous uterine surgery, multiple gestations, placenta previa, cervix dilatation higher than 3 cm, fetal or maternal complications requiring caesarean section, liquor anomalies, baby weight less than 4 kg, asthmatic individuals or women allergic to prostaglandins, as well as aberrant umbilical artery Doppler indices or non-stress tests.

Indications for labor induction were: Postdate pregnancy, pre-labor rupture of membranes and term pregnancy for mother with controlled medical disorder (PIH, controlled DM, PET, etc.)

Methods: The following procedures were performed on all of the study's participants:

Pre induction evaluation:

Verbal consent.

Full history taking: Personal background, with an emphasis on maternal age. Current History: Pay specific attention to warning signs such as headache, vision symptoms, edema of the face and fingers, severe vomiting, epigastric pain, loin pain, watery vaginal discharge, vaginal bleeding, diminished fetal movements, lower abdomen discomfort, and any drugs. Obstetric history, including any obstetric difficulties in previous pregnancies, such as ICU hospitalization or failure to induce labor. Gravity and parity are two concepts that come to mind while thinking about gravity and parity. Menstrual history: For accurate pregnancy dates, use the first day of the last menstrual cycle or an early u/s. Previous cervix surgeries (e.g. cautery, cerclage, cervical amputation or conization) or any surgical operations are examples of medical and surgical histories.

General examination: Vital signs and BMI.

Abdominal examination: Fundal level, fetal heart tones, and the existence of scars from past abdominal or pelvic procedures are also evaluated.

Vaginal examination: Cervical dilation, effacement, and regularity, cervical position, fetal station, and cervical length, condition of the membranes, pelvic adequacy, and fetal presentation are all assessed to determine the Bishop score of the cervix.

Scoring: A score of 0 to 2 or 0 to 3 is assigned to each component. The maximum score that may be achieved is 13.

Interpretation: With a score of 5 or below, labor is unlikely to begin without induction. A score of 9 or above suggests that labor will most certainly occur naturally. A low Bishop's score frequently suggests that induction will be difficult to achieve. According to some sources, only a score of 8 or above consistently predicts a successful induction.

Ultrasound assessment: Transabdominal: Complete transabdominal ultrasonographic examination in real time, involving validation of gestational age, baby number, viability, presentation, estimated fetal weight, placental position and location, quantity of liquor, and to rule out congenital defects. Transvaginal: Cervical length, funneling and posterior cervical angle.

Instrument: All patients in the research had transvaginal ultrasonography to determine the cervical length and posterior cervical angle, which was done using a Voluson P8 ultrasound equipment. Ultrasound machine Voluson P8: With a frequency of 3.5 MHz for the abdominal probe and 7.5 MHz for the vaginal probe. The posterior cervical angle was calculated as the angle between an imaginary line crossing the cervical canal and another tangential to the posterior uterine wall at its junction with the internal os in a sagittal plane at the level of the internal os, and funneling was recorded.

Non-stress test: To rule out patients who have non-reassuring non-stress tests, a 20-minute preinduction non-stress test will be performed.

Induction and monitoring of labor: The following are the conventional guidelines for induction of labor that were followed: Prostaglandin E1, (misoprostol): With a Bishop score of 7, I began looking for unfavorable cervices. Initial dose: 25 microgram vaginal tablet (ADWIA CO. S.A.E Egypt, vagiprost® 25 microgram). Oxytocin and/or Amniotomy: 5 units of oxytocin were infused into 500 mL of normal saline or "Ringer's solution" 6 hours after the last dosage of misoprostol, at a rate of 12 drops/minute.

Caesarean section was done in the following situations:- A fetal cardiac pattern that is consistently non-reassuring or aberrant. Induction of labor (induction) that failed (patient received 4 doses of misoprostol 25 microgram with 6 hours interval and no labor pains nor cervical dilatation or effacement were noted). Contractile abnormalities that persist. The age, gestational age, and initial Bishop Score of the women were also collected.

Statistical analysis: The statistical tool SPSS version 23 was used to code and input the data. For quantitative variables, mean, standard deviation, median, minimum, and maximum were used, while for categorical variables, frequencies (number of instances) and relative frequencies (percentages) were employed. The unpaired t test was utilized to compare the groups. The Chi square (x2) test was utilized to compare categorical data. When the anticipated frequency is less than 5, the exact test was utilized instead. The ideal cutoff values for detecting successful induction were discovered using a ROC curve and area under curve analysis. A P-value

RESULTS

Table 1: Indications for induction of labour:

The most common cause of induction was passed date (40 patients) 36 of them have delivered vaginally. The 2nd common cause was ROM (29 patients) 19 of them have delivered vaginally, then PIH (20 patients) 11 of them have delivered vaginally, then gestational diabetes (11 pregnant women) 4 of them delivered vaginally.

Table 2: Indications for induction of labour and mode of delivery

Fig. 1: Mode of Delivery and percentage

70 pregnant women were delivered vaginally and 30 by cesarean section. Indications of C.S. were failed induction (patient received 4 doses of misoprostol 25 microgram with 6 hours interval and no cervical dilatation & effacement were noted), failure to progress, fetal distress or abruption placentae.

Table 3: Relation between clinical data and outcome (success of induction):

Patients delivered vaginally had an average age of 26.10 ±4.08 years, whereas patients delivered via C.S. had an average age of 26.81 ±4.17 years. There was no statistically relevant link between induction of labor success and age, BMI, or infant weight. In addition, there was a statistically relevant link between gestational age and induction of labor success (P value 0.001).

Table 4: Bishop score, ultrasonographic criteria and mode of delivery

Patients delivered vaginally had a median Bishop score of 6.8 ±6.21, whereas patients delivered via C.S. had a median Bishop score of 4.57 ±.1.63.

Table 5: Funneling and mode of delivery:

We discovered a statistically substantial positive link between posterior cervical angle calculated by ultrasound funneling, Bishop Score, and induction success, as well as a statistically substantial negative association between cervical length and induction success, based on the previous data.

Table 6: Bishop Score's reliability in predicting effective induction vs. posterior cervical angle and cervical length:

Using a cut-off value Bishop Score 5.5 showed Sensitivity 73.5%, Specificity 81%, while the posterior cervical angle using a cutoff value 99.75 degree showed Sensitivity 91.8 %, Specificity 90.5 %, and cervical length using a cutoff value 34.5 mm showed Sensitivity 91.8 %, and Specificity 81 %

Fig. 2 : Bishop Score's reliability in predicting effective induction vs. posterior cervical angle and cervical lengt