Petrikovsky B M, Vintzileos A M, Lerer T
Department of Obstetrics and Gynecology, University of Connecticut Health Center, Farmington.
J Reprod Med. 1990 Feb;35(2):152-4.
The cyclic variation in fetal heart rate (FHR) patterns in preterm fetuses throughout labor was studied with a retrospective analysis of 49 FHR tracings. All fetuses were born preterm in good condition, and 92% exhibited the ability to change FHR cycles. A cycle was defined as an FHR pattern with consistent long-term variability in terms of amplitude range. The FHR cycles were significantly shorter in the second stage of labor as compared to the latent and active phases. Cycles of markedly diminished variability (less than or equal to 2.5 beats per minute) were observed in 16% of the fetuses during the latent phase and had a mean duration of 42 minutes, in 21% of the fetuses during the active phase with a mean duration of 68.3 minutes and in 8% of the fetuses during the second stage with a mean duration of 28.5 minutes. Knowledge of the normal length and frequency of FHR cycles is imperative for the correct interpretation of intrapartum FHR patterns in preterm fetuses.
