Premature BirthPregnancyObstetric Labor, PrematureInfant, PrematureInfant, NewbornGestational AgeBirth WeightInfant, Low Birth WeightPregnancy OutcomeFetal Membranes, Premature RuptureCerclage, CervicalInfant, Premature, DiseasesPregnancy ComplicationsEstradiolBirth RateProgestinsUterine Cervical IncompetenceInfant, Small for Gestational AgeRisk FactorsCervical Length MeasurementChorioamnionitisInfant MortalityHydroxyprogesteronesBirth CertificatesTerm BirthCervix UteriStillbirthMifepristoneTocolytic AgentsAdministration, IntravaginalProgesterone CongenersCorpus LuteumPregnancy, High-RiskUterusPregnancy Trimester, SecondInfant, Extremely PrematurePrenatal CareFetal DeathCohort StudiesMaternal AgeEstrusPregnancy Complications, InfectiousPregnancy, MultipleAmniotic FluidPrimary PreventionLuteinizing HormoneLabor, ObstetricBirth OrderProspective StudiesOvariectomyParityPregnancy, AnimalLuteal PhaseDelivery, ObstetricLogistic ModelsBirth IntervalsCervical RipeningPerinatal CareTime FactorsOvaryCesarean SectionOvulationReceptors, EstrogenDinoprostEndometriumMaternal ExposureRespiratory Distress Syndrome, NewbornHormone AntagonistsParturitionInfant, Very Low Birth WeightPessariesDevelopmental DisabilitiesLabor, InducedUnited StatesMultiple Birth OffspringSheepPregnancy Trimester, ThirdPlacentaOdds RatioCongenital AbnormalitiesVaginosis, BacterialEstrogensVaginaBronchopulmonary DysplasiaMyometriumFetal Growth RetardationIntensive Care Units, NeonatalMenstrual CycleChild DevelopmentTwinsIntensive Care, NeonatalExtraembryonic MembranesAbortion, Spontaneous20-Hydroxysteroid DehydrogenasesPre-EclampsiaRetrospective StudiesMothersSocioeconomic FactorsCase-Control StudiesChorionic Gonadotropin