Fetal Fibronectin Testing in Twin Pregnancies
Yes, fetal fibronectin testing can be performed in twin pregnancies and has demonstrated clinical utility for predicting preterm birth in this population. The test has similar predictive value in twins as it does in singleton pregnancies, with particularly high negative predictive value.
Clinical Application in Twin Pregnancies
Indications and Timing
- Fetal fibronectin (fFN) testing in twins should be performed:
- Between 24 weeks, 0 days and 34 weeks, 6 days of gestation 1
- When there are symptoms of preterm labor
- With intact amniotic membranes
- Minimal cervical dilation
Predictive Value
- In twin pregnancies with symptoms of preterm labor:
Comparison to Singleton Pregnancies
- Twin pregnancies show similar test characteristics to singletons, though with slightly lower specificity:
Clinical Utility and Limitations
Benefits
- A negative fFN test in twins provides reassurance that delivery is unlikely within the next 2 weeks 2, 3
- Can help reduce unnecessary interventions, hospitalizations, and treatments 3
- May be combined with cervical length measurement for improved prediction 4
Limitations
- The positive predictive value is relatively low (19%) 2
- Less useful for predicting delivery before 34 weeks compared to predicting delivery before 37 weeks 5
- Best predictive period appears to be between 27-30 weeks of gestation 5
Optimal Testing Strategy
Combined Approach
- The combination of fFN testing and cervical length measurement provides better prediction than either test alone 4, 6
- At 24 weeks, cervical length ≤25mm is the strongest predictor of spontaneous preterm birth 6
- At 28-30 weeks, a positive fFN result becomes a stronger predictor of delivery before 32 weeks 6
Risk Stratification
- Highest risk: Positive fFN + cervical length <20mm (significantly higher positive predictive value) 4
- Moderate risk: Either positive fFN or short cervix alone
- Lowest risk: Negative fFN with normal cervical length
Important Considerations
- Chorionicity does not affect the ability to perform fFN testing - it can be used in both monochorionic and dichorionic twins 3
- The American College of Obstetricians and Gynecologists notes that fFN testing has limited usefulness in low-risk women but may be valuable in high-risk populations like twins 1
- False positive results can occur with recent intercourse, vaginal bleeding, or vaginal examination
Remember that while a negative test is highly reassuring, a positive test should prompt consideration of interventions such as antenatal corticosteroids and closer monitoring, though it doesn't necessarily mandate immediate intervention.