Does cerclage location influence perinatal outcome?

Objective The study was undetaken to measure cerclage location within the cervix and to determine whether placement closer to the internal os is related to perinatal outcome. Study design We analyzed data collected during a randomized trial of cervical cerclage versus no cerclage that was conducted at Lehigh Valley Hospital between May 1998 and June 2001 in women with ultrasound findings of short cervix less than 25 mm or funneling between 16 and 24 weeksʹ gestation. Women who were randomly assigned to the cerclage arm had cervical measurements performed before cerclage, including dilation of the internal os, depth of membrane prolapse into the endocervical canal, cervical length below any funnel (distal length), and total cervical length (including any funnel). Measurements obtained after cerclage placement included the distance from external os to cerclage (A), and a repeat of the same four measurements. The distance from the external os to the cerclage (A) was divided by the total cervical length (B) and a cerclage to cervical length ratio (A/B) was calculated. The relationship between these measurements and gestational age at birth was assessed by linear regression analysis. Results Of 150 patients enrolled, 74 received a McDonald cerclage suture. Mean distal cervical length was1.9±0.9 cm before and 2.9±1.0 cm after cerclage (P = .001). The mean distance between the cerclage and external os (A) was 1.8±0.6 cm; the total cervical length after cerclage (B) was 3.6±0.9 cm. The mean cerclage to cervical length ratio (A/B) was 0.5±0.1. Linear regression analysis did not demonstrate a correlation between either the cerclage to external os measurement (A) or the cervical length ratio (A/B) and gestational age at birth (R2 = 0.0006 and 0.008, P = .8 and .6, respectively). Conclusion The length of the cervix below the level of cerclage is not related to duration of pregnancy in women treated with cerclage because of ultrasound evidence of cervical effacement.