Cervical length and funneling at 23 weeks of gestation in the prediction of spontaneous early preterm delivery

Objectives To establish the relationship of cervical length at 23 weeks of gestation to the risk of spontaneous delivery before 33 weeks and to determ ine the possible additional risk if funneling is present. Methods During a 36-month period, 6819 women with singleton pregnancies und erwent transvaginal sonographic cervical assessment at 22-24 weeks as a scr eening test for preterm delivery. The distribution of cervical length and t he prevalence of funneling, defined as dilatation of the internal os of ! S mm in width, were established. Women who underwent cervical cerclage, iatr ogenic preterm delivery or were lost to follow-up were excluded from furthe r analysis. In the remaining 6334 pregnancies, logistic regression was used to examine the contribution of cervical length and funneling to the risk o f spontaneous preterm delivery before 33 weeks. Results The median cervical length was 36 mm and in 1.6% of cases the lengt h was: IS mm. There was a significant inverse association between cervical length and percentage rate of spontaneous delivery before 33 weeks. Funneli ng of the internal os was present in about 4% of pregnancies and the preval ence decreased with increasing cervical length from 98% when the length was : IS mm to about 2S% for lengths of 16-30 mm and less than 1% at lengths of > 30 mm. The rate of preterm delivery was 6.9% in those with funneling com pared to 0.7% in those without funneling (chi (2) = 86.7, P < 0.0001). Howe ver, logistic regression analysis demonstrated that funneling did not provi de a significant additional contribution to cervical length in the predicti on of spontaneous delivery before 33 weeks (odds ratio for short cervix 24. 9, Z 4.43, P < 0.0001; odds ratio for funneling 1.8, Z = 0.84, P = 0.40). Conclusion In the prediction of preterm delivery, funneling does not provid e any significant contribution in addition to cervical length.