A 31-year-old woman, gravida 3 para 2, at 40 weeks gestation is in active labor. The patient has had a normal prenatal course. Her first pregnancy was an uncomplicated term vaginal delivery. Her second pregnancy ended with an emergent cesarean delivery for a nonreassuring fetal heart rate pattern. She has epidural anesthesia and is feeling mild pelvic pressure. Spontaneous rupture of the membranes occurred 15 minutes ago with blood-tinged amniotic fluid. Blood pressure is 124/76 mm Hg, pulse is 78/min, and respirations are 18/min. On pelvic examination, the cervix is 6 cm dilated and 80% effaced, and the fetal presenting part is at +1 station. The fetal heart rate tracing is shown in the exhibit. Which of the following is the most likely cause of this fetal heart rate pattern?

Question

A 31-year-old woman, gravida 3 para 2, at 40 weeks gestation is in active labor.  The patient has had a normal prenatal course.  Her first pregnancy was an uncomplicated term vaginal delivery.  Her second pregnancy ended with an emergent cesarean delivery for a nonreassuring fetal heart rate pattern.  She has epidural anesthesia and is feeling mild pelvic pressure.  Spontaneous rupture of the membranes occurred 15 minutes ago with blood-tinged amniotic fluid.  Blood pressure is 124/76 mm Hg, pulse is 78/min, and respirations are 18/min.  On pelvic examination, the cervix is 6 cm dilated and 80% effaced, and the fetal presenting part is at +1 station.  The fetal heart rate tracing is shown in the exhibit.  Which of the following is the most likely cause of this fetal heart rate pattern?

Quizplus · Accepted Answer

11ec25c8_da2d_e401_bc81_8b609a995df0_MD0003_00 This fetal heart rate tracing demonstrates moderate variability (average amplitude 6-25/min) and early decelerations. Early decelerations have a slow onset (?30 seconds from onset to nadir) and occur symmetrically with contractions. This results in the characteristic uniform, shallow deceleration with the nadir at the peak of the contraction and return to baseline at the end of the contraction. Early decelerations Early decelerations are caused by fetal head compression; these occur when the fetal head descends closer to the cervix, which contracts and causes narrowing of the fetal anterior fontanelle. The narrowed anterior fontanelle causes a transient alteration in cerebral blood flow and stimulates a vagal response, which slows the heart rate. Early decelerations are a benign, physiologic finding and do not indicate fetal hypoxia; therefore, these decelerations do not require intervention. (Choices B and E) Placental abruption and uteroplacental insufficiency typically cause late decelerations due to fetal hypoxia. Like early decelerations, late decelerations have a slow onset (?30 seconds from onset to nadir); but unlike early decelerations, they are delayed compared to contractions. Late decelerations begin after the onset of the contraction, nadir after the peak of the contraction, and return to baseline after the contraction. Late decelerations (Choice C) Umbilical cord compression results in variable decelerations, which have an abrupt onset (<30 seconds from onset in nadir) and a variable duration and depth with each deceleration. Variable decelerations are not always associated with contractions. variable decelerations (Choice D) Uterine rupture may cause bradycardia, variable decelerations, and late decelerations due to concomitant fetal hypoxia or umbilical cord compression (which occurs through the ruptured uterine scar). Educational objective: Early decelerations are uniform, shallow decelerations with gradual onset that occur symmetrically with contractions. They nadir at the peak of the contraction and return to baseline at the end of the contraction. Early decelerations are a benign finding caused by fetal head compression, which leads to a physiologic vagal response. References: A framework for standardized management of intrapartum fetal heart rate patterns. (http://www.ncbi.nlm.nih.gov/pubmed/17618744) The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. (http://www.ncbi.nlm.nih.gov/pubmed/18757666)

A 31-Year-Old Woman, Gravida 3 Para 2, at 40 Weeks