Cervical length measurement during mid-pregnancy as a predictor for preterm delivery

INTRODUCTION

During the transition between the prenatal and intrapartum periods, the uterine cervix undergoes significant physiological, biochemical, and morphological changes.

Preterm birth is defined by the World Health Organization as a baby born alive before the 37 weeks ¹.

Preterm birth continues to be a serious public health issue across the world. To reduce prematurity and alleviate its effects on preterm newborns, evidence-based strategies are required, particularly in low-resource settings.

Preterm birth data in most countries is of poor quality, making exact evaluation impossible at the global, regional, and national levels; nevertheless,

standardisation of definitions, measurement, and reporting would allow global comparisons of current data ².

Preterm birth and low birth weight are linked to a higher risk of illness and death, putting a strain on health, education, and social services, as well as on families. Preterm delivery and low birth weight may result in considerable health-care costs once the child is discharged from the hospital for the first time. It can also impose a strain on special education and social services, as well as newborns' families and caregivers, as well as society as a whole. In addition to the expenses indicated in the research, preterm delivery and low birth weight might have significant long-term repercussions that must be examined from an economic approach ³.

All these considerations had led various authors to search for a method that can reliably predict the occurrence of preterm birth. Various methods have been investigated: oncofetal fibronectin in vaginal and cervical secretions, screening for abnormal genital tract colonization, the use of biochemical markers (serum collagenase, CRH, relaxin, AFP, IL-6, IL-8, phosphorylated IGFP-1, lactoferrin). Different cervical scores have been devised. Finally, the use of ultrasound has been suggested and studied extensively for this purpose.

In 1969, Anderson and Turnbull reported that, in primi-parous women, cervical dilatation and effacement were related to the time in gestation at which labour started. However, they also pointed out that dilatation of the internal os after the 28^th week of gestation did not invariably predict either preterm birth or neonatal risk ⁴.

Techniques for measuring cervical length have been compared in non-pregnant women undergoing hysterectomy ⁽⁵⁾. Unfortunately, Digital cervix examination is subjective and involves a lot of interobserver variability. In addition, just the part of the cervix below the front vaginal wall is examined. The length was frequently underestimated by more than 13 mm when measured digitally. Ultrasonographic measures, on the other hand, were well associated with those obtained using a ruler on the postoperative material ⁶.

Varma et al. (1986)⁷, The average cervical length was determined to be between 35 and 40 mm in 30 low-risk pregnancies examined serially using transabdominal ultrasonography. Internal dilatation of up to 6 mm was considered typical.

Brown et al. (1986) ⁸ were the first to propose that transvaginal scanning was more likely to yield sufficient cervical pictures ⁹.

Murakawa et al. (1993) ¹⁰ the cervical length of 32 women who were at risk of preterm labour was investigated. None of the women who had a cervical length more than 30 mm gave birth prematurely. When the cervix was smaller than 30 mm, 65 percent of the babies were born prematurely. All women with a cervical length of less than 20 mm gave birth prematurely ¹¹.

Three large studies by Zorzoli (1994) ¹², Heath (1998)¹³, and Taipale (1998)¹⁴, studies use of transvaginal ultrasonography to evaluate cervical length to predict premature birth was investigated.

This study aims to determine the correlation between cervical length in mid-pregnancy and its use as a predictor for preterm delivery and the possible cutoff values.

PATIENTS AND METHODS

Type of Study:

This study is a prospective case controlled study.

This study was conducted at Sheikh Zayed Specialized hospital, Obstetrics and Gynaecology department. This was in the period from April 2019 till October 2020.

The study was conducted on an outpatient basis. It enrolled 200 women which were divided into two groups, as follows:

Group A (The study group):

Was involving 150 patients at midpregnancy (22 – 24 weeks). They fulfilled the following inclusion criteria:

Age: 20 – 35 years.

Parity: para 1 up to para 4.

22 – 24 weeks gestational age. Accurate dating was mandatory as confirmed by sure date of Last Menstrual Period (LMP).

History of previous preterm delivery or repeated abortions.

No medical disorders.

Singleton pregnancy.

Exclusion criteria were:

Smokers.

Congenital anomalies of uterus and cervix (Ultrasonography).

Multiple pregnancy.

Placental abnormalities.

Past history of cervical operations or cerclage.

Presence of cervical abnormalities.

Group B (The control group):

Included 50 women considered as low-risk for preterm delivery. These women fulfilled the above inclusion criteria for the study group, but they had NO history of preterm delivery or repeated abortions. One abortion was not an exclusion criterion. Primigravidae were excluded.

Methodology:

Every woman in both groups was subjected to:

Thorough history taking: stressing on the following points:

Personal data including name, age, occupation, address, phone numbers, length of marriage, and husband name and occupation.

Obstetric history: obstetric code, information about prior pregnancies (date, outcome, mode of delivery, gestational age at delivery, and any associated complications).

History of past medical or surgical disorders.

Full analysis of the current pregnancy ensuring the accuracy of LMP and the presence of symptoms suggestive of any complication.

Physical examination:

Pulse, Blood pressure, lower limb edema, other salient features of medical disorders.

Obstetric examination (fundal level, fundal grip, umbilical grip, pelvic grips, fetal heart sound auscultation).

Basic laboratory investigations:

Blood group and RH.

Complete blood picture.

Urine analysis.

Fasting blood sugar and 2hours post prandial blood sugar.

Hepatitis B and C.

Ultrasound examination, both transabdominal and transvaginal with measurement of the cervical length:

Fetal biometry (BPD, FL, AC), estimated gestational age, placenta (site and maturity), liquor (amount and turbidity).

Cervical length by transabdominal ultrasound.

Cervical length by transvaginal ultrasound.

Follow-up till delivery: patients were followed up till delivery and the gestational age at which labour occurred was recorded. Spontaneous preterm birth was defined as the onset of labour before 37 completed weeks.

Fig. 1: Transvaginal ultrasound scan showing landmarks found for cervical length measurement with an optimized plane for scanning.

Fig. 2: Transvaginal ultrasound scan showing a short cervix measuring 28.1mm in length. This case delivered preterm.

Fig. 3: Transvaginal ultrasound scan showing a relatively long cervix measuring 44.4mm in length. This case delivered at term.

Fig. 4: Transvaginal ultrasound scan showing a markedly shortened cervix with funneling.

Statistical analysis

The statistical programme for social sciences, version 20.0, was used to analyse the data (SPSS Inc., Chicago, Illinois, USA). The mean and standard deviation were used to convey quantitative data (SD). Frequency and percentage were used to convey qualitative data. As a result, the following p-value was declared significant: P-values of less than 0.05 were deemed significant, P-values of less than 0.001 were regarded very significant, and P-values of more than 0.05 were considered inconsequential.

RESULTS

Fig. 5: Flow chart

t-Independent Sample t-test; z-Mann-Whitney test; x2: Chi-square test

p-value>0.05 NS; *p-value

Table 1: Comparison between study group and control group according to baseline characteristics (n=188).

This table shows no statistically significant difference between groups according to baseline characteristics. No woman received prophylactic tocolysis in this study, before the time of ultrasound examination. The mean gestational age for preterm delivery was 37.60±2.56, in both the study and control groups.

t-Independent Sample t-test; **p-value

Table 2: Comparison between study group and control group according to transvaginal cervical length (n=188).

This table shows that a highly significant decrease mean in study group compared to control group according to transvaginal cervical length, with p-value

t-Independent Sample t-test; **p-value

Table 3: Comparison between study group and control group according to transabdominal cervical length (n=188).

This table shows that a highly significant decrease mean in study group compared to control group according to transabdominal cervical length, with p-value

x2: Chi-square test; *p-value

Table 4: Comparison between study group and control group according to outcome preterm delivery and term delivery (n=188).

This table shows the observed frequencies of the different outcomes (preterm vs. term delivery) in both study and control groups. Out of the 141 study women 48 delivered preterm (34%). Out of the 47 control women 6 delivered preterm (12.8%). This difference was stastically significant.

t-Independent Sample t-test; **p-value

Table 5: Comparison between preterm and term according to cervical length measured transvaginally in the study group (n=141).

In the study group, cervical length assessed transvaginally was considerably smaller in women who delivered preterm compared to those who delivered at term, as seen in this table.

t-Independent Sample t-test; *p-value

Table 6: Comparison between preterm and term according to cervical length measured transvaginally in the control group (n=47).

The cervical length assessed transvaginally in the control group was considerably smaller in women who delivered preterm compared to those who delivered at term, as seen in this table.

t-Independent Sample t-test; **p-value

Table 7: Comparison between preterm and term according to cervical length measured transvaginally in the all patients (n=188).

The cervical length measured transvaginally was substantially smaller in women who delivered preterm compared to those who delivered at term, as seen in this table.

t-Independent Sample t-test; **p-value

Table 8: Comparison between preterm and term according to cervical length measured transabdominally in the study group (n=141).

The cervical length assessed transabdominally in the study group was substantially smaller in women who delivered preterm than in women who delivered at term, as seen in this table.

t-Independent Sample t-test; **p-value

Table 9: Comparison between preterm and term according to cervical length measured transabdominally in the all women (n=188).

The cervical length measured transabdominally in women who delivered preterm was much smaller than in those who delivered at term, as seen in this table.

x2: Chi-square test; **p-value

Table 10: Comparison between preterm and term according to cervical length measured transvaginally in the study group (n=141).

The table describes the different outcomes in study cases with different cervical lengths measured transvaginally. This shows that with less than 40mm, 3 woman only delivered preterm and 68 women delivered at term.

x2: Chi-square test; *p-value

Table 11: Comparison between preterm and term according to cervical length measured transvaginally in the control group (n=47).

The table describes the different outcomes in control cases with different cervical lengths measured transvaginally. This shows no woman had cervical length less than 40mm, 2 woman only delivered preterm and 37 women delivered at term.

x2: Chi-square test; *p-value

Table 12: Comparison between preterm and term according to cervical length measured transvaginally in the all women (n=188).

The table describes the different outcomes in all cases with different cervical lengths measured transvaginally. This shows that with less than 40mm, 5 women only delivered preterm and 105 women delivered at term.

Table 13: Sensitivity, specificity, (+)ve predictive value and (-)ve predictive value of measuring cervical length transvaginally in study group.

This table shows the testing of 3 cut-off values for the cervical length measured transvaginally in the study group, as regarding their ability to predict preterm labour. The highest sensitivity (100%) was seen at 25mm. While 40mm showed the highest specificity it showed a marked reduction in sensitivity. The highest positive predictive value was seen at 40mm and the highest negative predictive value was seen at 30mm. The cut-off value of 30mm showed intermediate values for all criteria.

Table 14: Sensitivity, specificity, (+)ve predictive value and (-)ve predictive value of measuring cervical length transvaginally in control group.

This table shows the testing of 3 cut-off values for the cervical length measured transvaginally in the control group, as regarding their ability to predict preterm labour. The 25mm and 30mm values could not be assessed as no patients had values less than these figures.

Table 15: Sensitivity, specificity, (+)ve predictive value and (-)ve predictive value of measuring cervical length transvaginally in all cases.

This table shows the testing of 3 cut-off values for the cervical length measured transvaginally in both groups, as regarding their ability to predict preterm labour. The highest sensitivity (100%) was seen at 25mm. While 40mm showed the highest specificity it showed a marked reduction in sensitivity. The highest positive predictive value was seen at 40mm and the highest negative predictive value was seen at 25mm. The cut-off value of 25mm showed intermediate values for all criteria