Bed RestPlacentaHead-Down TiltWeightlessness SimulationWeightlessness CountermeasuresRestCardiovascular DeconditioningSpace FlightPlacenta DiseasesBedsPlacenta PreviaPlacenta AccretaPlacenta, RetainedWeightlessnessPregnancyOrthostatic IntoleranceTrophoblastsLower Body Negative PressurePhysiciansChorionic VilliMedical Staff, HospitalMaternal-Fetal ExchangeBed OccupancyPlacentationPregnancy ProteinsTime FactorsPhysician-Patient RelationsSupine PositionMuscular AtrophyPlasma VolumeMuscle, SkeletalEarly AmbulationExerciseHypotension, OrthostaticAttitude of Health PersonnelHypovolemiaFetusFamily PracticePre-EclampsiaVascular CapacitanceAmino Acids, EssentialImmobilization