Objectives: To determine the behavior of fetal oxygenation (FSpO(2)) in different patterns of fetal heart rate decelerations (FHR). Methods: A total of 787 decelerations were studied. Results: FSpO(2) decreased significantly during decelerations, especially when the alteration was prolonged. Conclusions: Modifications in FHR occur simultaneously with alterations in FSpO(2) although the latter do not persist in time. Different degrees of FSpO(2) seen prior to deceleration are an expression of fetal respiratory status. (C) 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.