FibronectinsObstetric Labor, PrematureTocolytic AgentsLabor Stage, FirstPregnancy, TripletCervix UteriCarbohydratesReceptors, FibronectinExtraembryonic MembranesGlycopeptidesFibroblastsTwinsPeptide FragmentsPregnancyGestational AgeElectrophoresis, Polyacrylamide GelTrypsinVaginaFetusAmino AcidsCell LineMolecular WeightPredictive Value of TestsGlycoproteinsSensitivity and SpecificityCell AdhesionBiological MarkersPregnancy OutcomeExtracellular MatrixIntegrin alpha5beta1IntegrinsLamininGelatinInfant, NewbornCollagenExtracellular Matrix ProteinsCells, Cultured