Ophthalmic ArteryBlood Flow VelocityUltrasonography, Doppler, TranscranialRegional Blood FlowMiddle Cerebral ArteryCerebrovascular CirculationCerebral ArteriesUltrasonography, DopplerPulsatile FlowMephentermineUltrasonography, Doppler, ColorHypocapniaRetinal ArteryBlood PressureUterusEphedrineUltrasonography, Doppler, PulsedArteriesCiliary ArteriesFetal Growth Retardation