Cerclage Should NOT Be Placed in This Twin Pregnancy
In a twin pregnancy at <24 weeks with a cervical length of 18 mm and no bleeding, cerclage is explicitly not recommended and should be avoided. 1
Primary Evidence Against Cerclage in Twins
The Society for Maternal-Fetal Medicine provides a GRADE 1B recommendation against routine use of cervical cerclage for cervical shortening in twin pregnancies, which applies to all cases including cervical lengths ≤25 mm before 24 weeks. 1 This is a strong recommendation based on high-quality evidence.
Why Cerclage Fails in Twins
An individual-patient-data meta-analysis of randomized trials found no benefit of cerclage in preventing preterm birth <34 weeks in twin gestations (adjusted OR 1.17,95% CI 0.23-3.79). 1
Even when the cervix is very short (≤10 mm), routine ultrasound-indicated cerclage does not improve outcomes in twins. 1
Twin pregnancies have higher intrinsic rates of preterm birth due to uterine over-distension and increased inflammatory mediators; these pathophysiologic mechanisms are not mitigated by mechanical cervical support such as cerclage. 1
The Critical Exception: Dilation Must Be Present
Cerclage may only be considered in twins when the cervix is ≤10 mm AND there is ≥1 cm of cervical dilation documented on physical examination. 1 Your patient has an 18 mm cervix with no bleeding, which does not meet these criteria.
A randomized trial (n ≈ 30) of twins meeting these strict criteria demonstrated a 70% reduction in preterm birth <34 weeks (70% vs 100%; RR 0.71,95% CI 0.52-0.96) with emergency cerclage. 1
The benefit was attributed specifically to cervical dilation, not to cervical shortening alone. 1
What You Should Do Instead
Surveillance Protocol
Perform serial transvaginal ultrasound of cervical length every 1-2 weeks from 14-24 weeks gestation to monitor for progression. 1
Conduct a physical examination if the cervical length drops to <11-15 mm, as 30-70% of patients will have cervical dilation ≥1 cm at that point. 2
Progesterone Consideration
Vaginal progesterone may be offered, though recent meta-analysis showed no significant reduction in preterm birth <33 weeks in twins (RR 0.77,95% CI 0.48-1.25). 1
The evidence for progesterone in twins with short cervix is weaker than in singletons, but it carries minimal risk. 1
Activity Modifications
Advise routine daily activities and light upper-body exercise, avoiding moderate-to-vigorous activity. 1
Do not prescribe bed rest, which offers no benefit and may be harmful. 1
Patient Education
Counsel on signs of preterm labor (uterine contractions, pelvic pressure, vaginal bleeding, fluid leakage) requiring immediate evaluation. 1
Educate on signs of infection (fever, uterine tenderness, purulent discharge) that necessitate urgent assessment. 1
Common Pitfall to Avoid
Do not extrapolate singleton-pregnancy benefits of cerclage to twin pregnancies—the benefits observed in singletons do not apply to twins. 1 This is a critical error that leads to unnecessary procedures with potential harm and no demonstrated benefit.
Contraindications to Consider
If dilation were to develop later, cerclage would still be contraindicated in the presence of: 1
- Active labor
- Chorioamnionitis
- Placental abruption
- Significant vaginal bleeding
- Fetal anomalies incompatible with life