Tightening McDonald cerclage suture under sonographic guidance

The technical factors contributing to failure of cerclage are not fully understood. The aims of this study were to assess the possibility of tightening the McDonald cerclage under ultrasound guidance and to examine the width and shape of the cervical canal before and after tightening the suture.

A prospective study was performed. The sole indication for cerclage placement was clinical history of cervical insufficiency. Cervical length and canal width were measured by transvaginal ultrasound, at 12-14 weeks' gestation, with the patient's bladder empty, after which the cerclage was performed. Tightening of the suture was performed under sonographic guidance (transabdominal or transrectal) until the cervical canal disappeared from view. After tying the suture, cervical length and the canal width were assessed sonographically.

Fifty-eight patients were enrolled in the study; 50 patients had singleton pregnancies and eight patients carried twins. The mean cervical length at the beginning of the procedure was 31 +/- 13 mm (median 30 mm, range 15-48 mm). The mean cervical canal width was 2.1 +/- 0.9 mm (median 2.0 mm, range 0.9-4.5 mm). The mean addition to the length of the cervical canal after the procedure was 11 +/- 0.8 mm (median 1.0, range 8-19 mm). No complications were noted during the procedures. An interesting sonographic finding was an hourglass shape of the cervical canal after the procedure in 16 patients. Of 58 patients, 47 delivered at term, 10 delivered preterm and one miscarried at 18 weeks. Nine of 10 patients with preterm delivery had an hourglass-shaped sonographic appearance of the cervical canal after the procedure.

McDonald cerclage can be tightened under ultrasound guidance. The sonographic appearance of an hourglass shape of the cervical canal following suture tightening may be a risk factor for preterm delivery.