Serial transvaginal sonographic measurement of cervical dimensions after 20 weeks of gestation in South Indian women

This study was conducted with objective to assess serial changes of cervical dimensions during pregnancy from mid second trimester till delivery by transvaginal sonography. It comprises 50 healthy pregnant women who underwent serial transvaginal ultrasound every four week from 20th week of gestation till delivery. Cervical length and width were measured. The gestational age at delivery was recorded. Cervical changes were analysed using student - t test with three classifying factors; gestational age (<37 & >= 37 weeks), parity (nulliparous & parous) and body mass index (<= 23 & >23). Percentile charts were established for cervical length and width from 20th week of pregnancy till delivery. The associations between cervical dimensions and gestational age, parity and body mass index were calculated by multiple linear regression analysis. Cervical length decreased gradually from 4.05 cm from 20th week to 3.25 cm at term. The equivalent values were 2.98 cm and 3.86 cm for cervical width measurement showing opposite trend. The rate of cervical length reduction was significantly higher in preterm delivery group compared to term delivery group (0.65 mm vs. 0.37 mm per week of gestation, p < 0.0001). No difference in cervical dimensions with respect to parity was observed. Mean cervical length at any given gestation was longer in patients with BMI > 23; however this was statistically significant only in the beginning (at 20th and 24th week of gestation). Cervical length decreases gradually through out the gestation where as cervical width increases and these changes are not affected by parity. The knowledge of pattern of change in cervical length may help in early detection of preterm labour.