Bed RestPremature BirthInfant, PrematureInfant, NewbornPregnancyObstetric Labor, PrematureBirth WeightHead-Down TiltInfant, Low Birth WeightWeightlessness SimulationGestational AgePregnancy OutcomeWeightlessness CountermeasuresCongenital AbnormalitiesRestPregnancy ComplicationsAbortion, VeterinaryInfant, Premature, DiseasesCardiovascular DeconditioningPostoperative ComplicationsBronchopulmonary DysplasiaFetal DeathSpace FlightAbortion, SpontaneousBedsInfant MortalityInfant, Small for Gestational AgePregnancy Complications, InfectiousRisk FactorsWeightlessnessRespiratory Distress Syndrome, NewbornRetrospective StudiesAnimals, NewbornOrthostatic IntoleranceBirth RateLower Body Negative PressureTreatment OutcomeTime FactorsIntraoperative ComplicationsBirth OrderBirth CertificatesBed OccupancyFollow-Up StudiesProspective StudiesEarly AmbulationSupine PositionMuscle, SkeletalMuscular AtrophyExercisePlasma VolumeHypotension, OrthostaticDiabetes ComplicationsHypovolemiaImmobilizationSpinal PunctureVascular CapacitanceAmino Acids, EssentialBirth IntervalsObstetric Labor ComplicationsBirth InjuriesCohort Studies