Objective: Preterm birth (birth before 37 weeks of completed gestation) is the leading cause of neonatal death, and has an incidence of 5-13% which is believed to be on the rise. The objective of this study was to determine the rate of spontaneous preterm birth and investigate the relationship between preterm birth and cervical length in a pregnant Asian population.
Materials and methods: A prospective observational study between September 2010 and November 2013 was performed at KK Women's and Children's Hospital, Singapore. 1013 women with single viable pregnancies were recruited at less than 14 weeks of gestation between September 2010 and November 2013, excluding those with multiple gestation, pre-existing autoimmune or renal disease or those with current pregnancies complicated by aneuploidy or fetal anomalies. Participant characteristics were obtained from an interviewer-administered questionnaire at the first recruitment visit. Cervical length was measured using ultrasound at each of the 4 antenatal visits (Visit 1: < 14 weeks, Visit 2: 18-22 weeks, Visit 3: 28-32 weeks and Visit 4: > 34 weeks) using the Fetal Medicine Foundation protocol. Data on pregnancy outcomes were obtained from obstetric case notes and records. The main outcome measure examined in this study was that of spontaneous preterm birth and its relationship to cervical length.
Results: There was a significantly shorter cervical length both in the 2nd trimester (18 to 22 weeks) and the 3rd trimester (28 to 32 weeks) in the preterm birth group compared to the term birth group (p = 0.028 and p < 0.001 respectively). In the first trimester (11 to 14 weeks), there was no statistically significant difference in cervical length between the two groups (p = 0.425). ROC curve analysis for cervical length in the preterm birth group for 18 to 22 weeks and 28 to 32 weeks showed an AUC of 0.605 and 0.725 respectively. At 28 to 32 weeks of gestation, a cut-off level at 2.49 cm has a sensitivity of 54.8%, specificity of 82.5%, negative predictive value of 97.9% and positive predictive value of 11.1%.
Conclusion: There is a significantly shorter cervical length in the 2nd and 3rd trimester in the preterm birth group. Cervical length is a moderate predictor of preterm birth with good negative predictive value and a relatively good specificity. Ultrasound cervical length screening for pregnant Asian women between 18 and 22 weeks of gestation with a cutoff of ≥ 2.48cm can help to identify a group of women who are at risk for preterm birth.