Cervical Length Measurement at Term Pregnancy as a Predictor of Time of Onset of Labour and Mode of Delivery: A Longitudinal Study

Introduction: Cervical assessment has moved from digital examination to sonographic evaluation in recent years. Predicting the time of onset of labour and mode of delivery at term is a great concern for both the pregnant woman and her relatives.

Aim: To predict the time of onset of labour and mode of delivery by Transvaginal sonographic measurement of cervical length at term.

Materials and Methods: This longitudinal study was conducted in the Department of Obstetrics and Gynaecology, SRM Medical College Hospital and Research Centre, Kattankalathur, Tamil Nadu, India, from March 2021 to August 2021. All low-risk singleton pregnancies between 38-40 weeks of gestation were included. Cervical length (in mm) was measured transvaginally by the principal investigator between 38 and 40 weeks. When the labour sets in the duration between cervical length measurement and the onset of labour, duration of labour and mode of delivery were noted. Pearson correlation coefficient was used to quantify the association between cervical length and time of onset of labour and duration of labour.

Results: In the study, 164 low-risk patients (143 Primigravida patients+21 Multigravida patients) between 38-40 weeks were included. In patients with spontaneous onset of labour, 45 (70.3%) had labour onset within 120 hours (5 days) when cervical length was ≤30 mm, when compared with 7 (22.58%) when cervical length was >30 mm (p=0.001). In patients with cervical length ≤30 mm, vaginal delivery occurred in 47 (73.43%) (p=0.019). In women with induced labour with cervical length ≤30 mm, 13 (61.9%) had labour onset within 120 hours when compared to 15 (30.6%) in women with cervical length >30 mm (p=0.02). Vaginal delivery occurred in 5 (29.41%) of women when cervical length was ≤30 mm compared to 32 (65.30) in women when cervical length >30 mm which may be attributed to other causes. There was a significant positive correlation between cervical length and time of onset of labour (Correlation coefficient=0.221, p-value=0.004). There was a negative correlation between cervical length and duration of labour which was not statistically significant (Correlation coefficient=-0.108, p=0.25). There was no significant difference in mean cervical length measurement between vaginal delivery and caesarean section.

Conclusion: Transvaginal cervical length measurement at term positively correlates with time of onset of labour but not with duration of labour and mode of delivery.