Decreased amniotic fluid during pregnancy (i.e., oligohydramnios) is associated with more frequent variable decelerations as the amniotic fluid has a protective role on the fetal umbilical cord. This is followed by occlusion of the umbilical artery, which results in a sharp deceleration as the fetal blood supply is suddenly restricted. Pressure on the cord initially occludes the umbilical vein, which results in an acceleration (i.e., an increase of the FHR) and indicates a healthy response. Some triggering circumstances include low maternal blood pressure (i.e., hypotension) from the epidural analgesia, dehydration of the mother, anemia of the mother, rapid uterine contractions, placental abruption (i.e., the early separation of the placenta from the uterus before labor), and fetal hypoxia (i.e., low oxygen levels). Lastly, variable decelerations are caused by compression of the umbilical cord. Any condition that predisposes decreased uteroplacental blood flow can cause late decelerations. Late decelerations are caused by uteroplacental insufficiency, which is a decrease in the blood flow to the placenta that reduces the amount of oxygen and nutrients transferred to the fetus. These decelerations are completely benign as they do not affect fetal oxygenation and, therefore, do not require treatment. Stimulation to the vagus nerve can cause a decrease in the FHR seen as a deceleration that disappears immediately after the contraction. Especially a few weeks before labor, when the baby is tightly fitted in the uterus, the pressure applied to the fetus during uterine contractions may bend the fetus’s neck, causing vagal stimulation. As the uterine muscles get tighter and shorter, the size of the uterus decreases, thereby limiting the available space for the fetus. The causes of fetal decelerations mainly depend on the types of decelerations.Įarly decelerations in FHR are caused by compression of the fetus’s head during a uterine contraction. What causes decelerations in fetal heart rate? They often resemble the letter “U,” “V” or “W” and may not have a constant relationship with uterine contractions. They typically occur during the first and second stages of labor (i.e., the initial contractions and dilation of the cervix leading to the delivery of the infant, respectively) and vary in shape, duration, and intensity. These decelerations are associated with maternal and fetal conditions (e.g., maternal hypotension from epidural, placental abruption). Finally, variable decelerations are the most common type of fetal deceleration. As opposed to early decelerations, late decelerations often begin just after a contraction, with their lowest point occurring after the peak of the contraction. Late decelerations are also uniform in shape however, their onset and return to baseline are gradual. They begin near the onset of a uterine contraction, and their lowest point occurs at the same time as the peak of the contraction. FHR baseline usually ranges from 120-160 beats per minute (bpm) however, with fetal decelerations, the heart rate usually drops about 40bpm below baseline.įetal decelerations are classified into three categories (e.g., early, late, and variable) according to their shape and timing relative to uterine contractions.Įarly decelerations are benign and uniform in shape. Electronic fetal monitoring is used to record the heartbeat of the fetus and the contractions of the mother’s uterus before and during labor. Walker What is a fetal deceleration?įetal decelerations refer to temporary but distinct decreases of the fetal heart rate (FHR) identified during electronic fetal heart monitoring. Back Fetal Decelerations What Is It, Causes, and MoreĮditor s : Alyssa Haag, Józia McGowan, DOĬopyeditor : David G.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |