Objective: To compare the effects of cerclage performed with a modified Shirodkar procedure or with McDonald's technique using transvaginal ultrasound measurement of the distance between the external os and the suture.
Materials and methods: We performed a retrospective study of all patients who underwent a prophylactic cerclage with either the modified Shirodkar procedure or the McDonald's technique over a 3-year period. Physicians chose the cerclage technique according to their own preferences. Transvaginal ultrasound examination of the cervix was performed 2 weeks after the cerclage to measure its functional length and the distance between the external os and the cerclage.
Results: During the study period, 14 patients had a cerclage with the modified Shirodkar procedure and 19 patients with the McDonald's technique. Twelve of these 33 patients (36.4%) delivered before 37 weeks. The obstetric characteristics of the patients in both groups were similar. There were no significant differences between the Shirodkar and McDonald groups as to the functional cervical length before (31.3 +/- 8.7 vs. 35.6 +/- 9.7 mm, respectively) or after (37.0 +/- 7.3 vs. 36.1 +/- 7.9 mm) cerclage, the distance between the external os and cerclage (16.7 +/- 3.8 vs. 14.0 +/- 5.2 mm), or the number of deliveries before 32 (0 vs. 2) and 34 (1 vs. 3) weeks.
Conclusion: The anterior colpotomy of the Shirodkar procedure increased the distance between the external os and the cerclage by a mean of 2.7 mm. This slight gain does not justify exposing the patient to the risks related to this procedure. When cerclage is necessary, McDonald's technique seems preferable.