Multiple Birth OffspringPregnancy, MultipleTripletsBirth RateBirth WeightPregnancyQuadrupletsReproductive Techniques, AssistedMaternal AgeTwinsInfant, NewbornInfant, Low Birth WeightPremature BirthBody WeightPregnancy OutcomeInfant MortalityBirth OrderGestational AgeFetal DeathEmbryo TransferWeight GainCongenital AbnormalitiesFertilization in VitroWeight LossPregnancy ComplicationsBirth CertificatesPrenatal Exposure Delayed EffectsPerinatal CareInfertilityDelivery, ObstetricInfant, PrematureRisk FactorsPregnancy Reduction, MultifetalLive Birth