Multiple Birth OffspringPregnancy, MultipleTripletsPregnancyBirth RateBirth WeightQuadrupletsReproductive Techniques, AssistedTwinsMaternal AgeInfant, NewbornGestational AgePremature BirthPregnancy OutcomeInfant, Low Birth WeightInfant MortalityFetal DeathBirth OrderEmbryo TransferCongenital AbnormalitiesFertilization in VitroPregnancy ComplicationsPrenatal Exposure Delayed EffectsInfant, PrematureBirth CertificatesPerinatal CareInfertilityDelivery, ObstetricLive BirthFetusPregnancy, AnimalPregnancy Reduction, MultifetalRisk Factors