A prospective study of prediction of preterm delivery by cervical assessment by transvaginal sonography

Introduction

Approximately 15 millions babies are born premature every year i.e. more than 1 in10. Almost 1 million children die every year due to complications of preterm birth. Many survivors face lifetime disability which include learning disabilities, visual and hearing problems. Globally prematurity is leading cause of death in children under the age of 5 years. India is among the top ten countries with greatest number of preterm birth.^[1]

Preterm birth as defined by WHO, American academy of Paediatrics and American Congress of Obstetrician and Gynaecologist, is the birth of a baby before 37 weeks of gestation. Preterm labour has multifactorial etiopathogenesis. A variety of maternal and fetal factors are known to increase the risk of preterm labour. Although there are unique aspects to each cause of preterm labour these diverse processes culminate in common end point which is premature cervical dilation and effacement premature activation of uterine contractions.^[2]

The fundamental change in the strategy of the preterm birth prevention has been the understanding of a need to intervene earlier in the development of a pathophysiology leading to this undesired outcome of preterm labour. The concept of tocolysis has been shown to beneficial in other outcome in preparation for preterm birth such as gaining opportunity for steroid benefit to enhance fatal neonatal functions or to allow the transport of a patient from facility without the potential for neonatal intensive care to one with that capability.

Several methods like home uterine monitoring, cervical examination, fetal fibronectin in cervico-vaginal secretions etc. have been used for identifying women at risk of preterm delivery. But these methods have been associated with either low sensitivity or specificity or are not cost effective. Sonographic evaluation of cervix determined by trans-abdominal or trans-vaginal scanning has significant role to predict the preterm labour. Sonographic evaluation is more precise procedure as compared to digital assessment. When performed by trained operator cervical length analysis using TVS is safe, highly reproducible more predictive than TAS screening.

Aims

To find out the effectiveness of assessment of cervical length by TVS in predicting preterm delivery.

Objective

To find out the corelation of short cervix, open internal os and funnelling with preterm delivery.

Materials and Methods

Observational prospective study was done in department of obstetrics and gynaecology at GMC Gondia for 1 year from 1 Jan 2019 to 31 Dec 2019 with a sample size of 100.

100 women who underwent TVS assessment of cervix regularly followed up and delivered in one institution were distributed in two groups-

Group A- with cervical length <25mm

Group B- with cervical length >= 25mm

Results

The maximum number of patients in the study belong to the age group of 23-27 years with mean age±SD being 25.95+-3.8 years. Out of total 100 patient, 44 patients were primigravida and 56 patients were multigravida.

In similar study done by Kore SJ et al ^[3] all patient enrolled in study underwent TVS between 22-24 weeks of gestation,majority of the women were in the age group of 20-30 years, 58 were primigravidas and 57 were multigravidas. The mean cervical length in all these women was 36.43±7.98 mm. The values in primigravidas and multigravidas were almost similar.

Out of total 14 cases with open internal os 9(64.28%) delivered preterm and out of 18 cases of funneling 6 (33.33%) delivered preterm. Among those with closed internal os, only 4.41% delivered preterm. This corresponds to study conducted by Bhonsale et al. Bhosale et al.^[4] reported that of the 88 patients that had preterm delivery, in 36 patients there was presence of funneling and only 2 of these could carry their pregnancies till term and 34 of them i.e. 94.4% had preterm deliveries.

GR Shinde et al.^[5] reported mean gestational age at birth in group B (cervical length > 25 mm) was 38.94 ± 2.3 weeks and in group A (Cervical length ≤ 25 mm) 35.3 ± 3.2 weeks with 75% preterm deliveries in group A.

Among 18 preterm deliveries 15 patients (83.33%) has cervical length < 25 mm and 3 patients(16.66%) of them had cervical length >=25mm. This shows that most of the preterm deliveries short cervical length.

Statistic analysis done by chi-square test.

Applying chi – square test

The chi-square statistic is 31.4728. (Chi 2 =31.47   DF=1)

The two-tailed P value is less than 0.0001. By conventional criteria, this difference is considered to be extremely statistically significant.

Discussion

In our study mean cervical length was 30.0mm ± 6.68(SD). Among 29 patients with cervical length <25mm 51.72% delivered preterm and rest 48.27% delivered term, whereas out of 71 patients with cervical length >/= 25mm only 4.22% delivered preterm and majority of (95.77%) patients delivered at term. This is statistically significant and suggest that shorter the cervical length more is the risk of preterm delivery. This is consistent with the result of study by Mathur S et al^[6] and Tanvir et al^[7] which also shows positive correlation.

Hence, it can be concluded that nearly 1/2 to 2/3 of women with short cervical length <25mm deliver preterm unless certain precautions are taken.

Though preterm birth occurs in approximately 5-15% of all deliveries it accounts for the major bulk of perinatal and especially postnatal deaths. The risk of neonatal morbidity and mortality mainly depends on the gestational age at delivery. Survival rate increases with increasing period of gestation. In a developing country like ours, where intensive care facilities are often unavailable, mortality figures would be much higher at a lower gestation period at delivery.

The main reason for low success rate of tocolytic therapy is failure to detect patient at an early stage. Thus it becomes essential to identify women, both symptomatic and asymptomatic, who are at risk of preterm delivery early enough so that an optimum treatment in the form of tocolysis or cerclage can be given in time. Unfortunately current methods of identifying women at risk of preterm delivery like a scoring system based on demographic factors and digital examination of cervix have low sensitivity and specificity. Objective methods such as evaluation of the presence of cervico-vaginal fibronectin, direct or indirect assessment of subclinical infection including bacterial vaginosis, and assessment of cervical or amniotic cytokine concentration are accurate, but expensive and often unavailable.

Ultrasonographic assessment of the cervix has emerged as an alternative method to objectively assess cervical length and morphology for prediction of preterm labour. Acceptability and repeatability of this procedure were found to be good and cost- effective.^[8]

Conclusion

Short cervical length predispose to preterm labour. The risk of preterm delivery is inversely proportional to cervical length. Doing a TVS measurement of cervical length between 20-25 weeks of gestation can be a helpful strategy to identify pregnant women at risk of preterm delivery.

Source of Funding

None.

Conflict of Interest

The authors declare no conflict of interest.