Multiple Birth OffspringPregnancy, MultipleTripletsFetusBirth RatePregnancyQuadrupletsBirth WeightReproductive Techniques, AssistedMaternal AgeTwinsInfant, NewbornPremature BirthInfant, Low Birth WeightGestational AgePregnancy OutcomeFetal DeathInfant MortalityBirth OrderEmbryo TransferCongenital AbnormalitiesFertilization in VitroPregnancy ComplicationsPrenatal Exposure Delayed EffectsBirth CertificatesPerinatal CareInfertilityPregnancy Reduction, MultifetalDelivery, ObstetricLive BirthCampylobacter fetusInfant, PrematureRisk Factors