Large loop excision of transformation zone and cervical length in the prediction of spontaneous preterm delivery

Objectives To investigate the association between previous large loop excision of transformation zone (LLETZ) and risk for subsequent spontaneous preterm delivery (sPD) and whether this effect is reflected in the measurement of cervical length at midgestation. Design and setting A secondary analysis of data from women recruited for clinical trials of interventions to prevent preterm labour. Population A total of 26 867 women with singleton pregnancies attending for routine antenatal care. Methods Transvaginal sonographic measurement of cervical length was carried out at 20 + 0 to 24 + 6 weeks. Logistic regression analysis was used to determine the significant predictors of sPD among maternal characteristics, obstetric history, previous history of LLETZ and cervical length. Main outcome measures Spontaneous preterm delivery. Results In the 473 women who had undergone LLETZ, compared with the 25 772 without a history of LLETZ, the rate of sPD before 34 weeks of gestation was higher (3.4 versus 1.3%, P = 0.0002) and the median cervical length was shorter (32 mm versus 34 mm, P < 0.0001). Regression analysis demonstrated that in the prediction of sPD there were significant contributions from racial origin, cigarette smoking, previous preterm delivery and LLETZ and the detection rate of sPD was 29.8%, at a falsepositive rate of 10%. However, after addition of cervical length, LLETZ did not remain a significant predictor in the model, which detected 52.6% of sPD, at a false-positive rate of 10%. Conclusions LLETZ increases the risk of sPD, even after adjustment for maternal risk factors. The effect of a previous LLETZ on sPD in a subsequent pregnancy is reflected in the measurement of cervical length at mid-gestation.