This study examined fetal heart rate (FHR) variables during maternal sleep in subsequent siblings of infants who died of sudden infant death syndrome (SIDS) and who are thus at increased statistical risk for SIDS, and controls. Four findings differentiated the tracings of subsequent siblings of SIDS infants and controlscolon; 1) FHR variability in subsequent siblings of SIDS infants ranged between 11 and 25 beats/min, compared with 6 to 10 beats/min in controls (P.001). 2) Bradycardia was more frequent in subsequent siblings of SIDS infants. 3) FHR accelerations (more than 150 beats/min) followed by heart rates below 120 beats/min were elevated in subsequent siblings of SIDS infants (P.01). 4) Strong respiratory arrhythmia was more frequent in subsequent siblings of SIDS infants. These siblings exhibited more reactive FHR patterns. Although these data cannot be interpreted as clinical markers identify the infant who will die of SIDS, they are compatible with the hypothesis that mild chronic hypoxia is associated with risk for SIDS.
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