Ultrasound Measurement of Twin Dividing Membrane Thickness and Risk of Spontaneous Preterm Birth

OBJECTIVE: To determine if prenatal ultrasound measurements of dividing membrane thickness (DMT) can predict spontaneous preterm birth (sPTB) and histologically-confirmed chorionicity in twin pregnancies. STUDY DESIGN: Prospective cohort in which DMT was measured by transabdominal ultrasound, both parallel and perpendicular to the transducer. RESULTS: A total of 73 twin pregnancies were included: 54 dichorionic-diamniotic (DCDA) and 19 monochorionic-diamniotic (MCDA). Overall, 75.9% of DCDA and 100% of MCDA gestations delivered preterm (p<0.02); these were categorized as spontaneous in 78.0% of DCDA and 84.2% of MCDA gestations. Ultimately, no association between DMT and sPTB was identified. However, DMT was associated with overall PTB at <37 weeks, with receiver operating characteristic curve analyses resulting in an area under the curve (AUC) of 0.756 for parallel (p<0.006) and 0.725 for perpendicular (p<0.016) measurements with cutoff values of 2.6 and 2.7 mm, respectively. The AUC to predict monochorionicity was 0.950 (p<0.001) for parallel measurements and 0.883 (p<0.001) for perpendicular measurements, with cutoff values of 1.9 and 1.8 mm, respectively. CONCLUSION: Ultrasound-measured DMT is not associated with sPTB in twin pregnancies. DMT <2.6 mm is associated with an increased risk of overall PTB, though the etiology is uncertain. Monochorionicity can be determined by DMT <1.9 mm.