Decelerations are categorized as early, late, variable, or prolonged. FHR decelerations are defined according to their visual relationship to the onset and end of a contraction and by their shape. Early decelerations
Visually apparent gradual decrease in and return to the baseline FHR associated with uterine contractions. The onset, nadir, and recovery of the deceleration generally correspond to the beginning, peak, and end of the contraction. Early decelerations are thought to be cause by transient fetal head compression and are considered a benign finding. May also occur during vaginal examinations, as a result of fundal pressure, and during placement of the internal mode of fetal monitoring. When present, they usually occur during the first stage of labor when the cervix is dilated 4 to 7 cm but can also be seen during the second stage when the woman is pushing. Since early decelerations are considered to be benign, interventions are not necessary but they should be identified so they can be distinguished from late or variable decelerations, for which interventions are appropriate. Late decelerations
Visually apparent gradual decrease in and return to baseline fetal heart rate associated with uterine contractions. The deceleration begins after the contraction has started, and the lowest point of the decelerations occurs after the peak of the contraction. The deceleration usually does not return to baseline until after the contraction is over. Uteroplacental insufficiency causes late decelerations. Persistent and repetitive late decelerations indicate the present of fetal hypoxemia stemming from insufficient placental perfusion during uterine contractions. If recurrent or sustained, late decelerations can lead to metabolic academia. They should be considered an ominous sign when they are uncorrectable, especially if they are associated with absent or minimal variability and tachycardia. Several factors can disrupt oxygen transfer to...
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