Ultrasound Examination at 37 Weeks Gestation in the Prediction of Pregnancy Outcome: The Value of Cervical Assessment

INTRODUCTION: Antenatal assessment is based on the clinical examination which is carried out at 4-weekly intervals till 28 weeks, at 2 weekly intervals till 36 weeks and every week thereafter to delivery. The main objective of such care is to diagnose and manage the maternal and fetal complications appropriately and identify the major problems that may arise in labour and delivery. In the last few years, ultrasonography has become an integral part of antenatal care, playing a central role in accurately dating the pregnancy and screening for fetal abnormalities, multiple gestation etc,. Furthermore, Doppler ultrasound at mid-gestation may be useful predictor of pregnancies at high risk for pre-eclampsia and fetal growth restriction and sonographic measurement of cervical length identifies pregnancies at high- risk of spontaneous preterm delivery. In third trimester, ultrasound is selectively used to diagnose and manage the problems suspected from clinical examination, such as fetal growth restriction, macrosomia, malpresentation, antepartum haemorrhage. Recent studies have reported that sonographic measurement of cervical length is a useful predictor of the likelihood of successful induction of labour. Our aim is to determine the potential value of a routine ultrasound examination in low-risk pregnancies at 37 weeks for diagnosis of unsuspected fetal growth restriction, macrosomia, malpresentation and in the prediction of the onset and outcome of labor, including the risk of prolonged pregnancy and caesarean section for failed induction or lack of progress in labour. AIM OF THE STUDY: 1. To examine the potential value of routine measurement of cervical length in singleton low-risk pregnancies at 37 weeks of gestation in the prediction of onset and outcome of labour. MATERIALS AND METHODS: STUDY DESIGN: PROSPECTIVE OBSERVATIONAL STUDY. METHODOLOGY: The study was conducted in Govt. RSRM Lying in Hospital, Chennai during the period of September 2020 to September 2021 after getting approval from the Institutional Ethical Committee. The entire study population was recruited from antenatal clinic from Government RSRM lying in Hospital and offered the 37-week scan and followed up for the outcome of labour. At the 37-week clinic the maternal blood pressure and weight was measured, abdominal examination carried out to determine the presentation and measurement of symphysiofundal height. Trans-abdominal ultrasound was performed for the determination of fetal presentation and placental site and fetal head and abdominal circumference, femur length and amniotic fluid index and Doppler studies for measurement of pulsatality index in the umbilical artery and fetal middle cerebral artery. Trans-vaginal sonography was then performed for the measurement of cervical length. Three measurements were obtained and the shortest, technically best measurement in the absence of uterine contraction was recorded. RESULTS: 370 primigravida patients were included in the study in the age group of 18-40 years. The mean age group being 26 years. Postdatism is the only indication for induction. In a similar study by Anikwe [et al.] around 60 patients were included. For the patients in the study group cervical length was measured from 37 weeks of gestational age. They were evaluated whether the patient went into spontaneous labour or needed induction of labour and the mode of delivery at the end. Parturient with cervical length < 3 cm had a higher relative risk of short labour duration when compared to longer cervical length. This finding of was also supported by the work of Tan [et al.], which again reported that ultrasound measured cervical length prediction had superior sensitivity in the prediction of onset of labour. The patients in the study group had cervical lengths in the range of 1 to 5 cm. 48.3% patients had a cervical length 3 cm. In the study conducted by Pandis [et al.] the median TVS length was 2.5 cm. In our study 255 patients entered spontaneous labour of which 147 patients with cervical length of 2-3 cm delivered by labour natural;Of 155 patients in induction group, 44 patients with cervical length 4 to 5 cm were induced, of which 26 patients were delivered by LSCS. On analyzing mode of delivery in our study, 248 patients were delivered by labour natural, 97 patients by LSCS, 25 patients by instrumental delivery. 23 cases of LSCS were done for Failed induction and 50 cases for Failure to progress. CONCLUSION: Ultrasound examination has become an integral part of every antenatal in monitoring the fetal growth and well being. The high association between cervical length and onset of labour may provide adequate information to both the pregnant women and the attending obstetrician in planning the subsequent management of delivery.Induction of labour is one of the most common obstetric practices being carried out in the world. Compared to spontaneous onset of labour, induction of labour is complicated by a higher rate of Caesarean section. This difference is greater for nulliparous women with unfavourable cervix. As induction of labour is associated with its own risks,knowing that there is high chance of delivery in subsequent week if the cervical length is short may allow the patient and clinician to await spontaneous labour. Conversely, if the cervical length is longer, induction of labour may then be carried out. As emergency cesarean section are the worst mode of delivery in terms of maternal morbidity,c oncentrating on better antenatal advice and management would be the cornerstone to more optimal care