A 30-year-old woman, gravida 1 para 0, at 42 weeks gestation comes to the hospital with regular and painful uterine contractions. On admission, temperature is 36.1 C (97 F), blood pressure is 110/70 mm Hg, and pulse is 92/min. Estimated fetal weight is 3.8 kg (8.4 lb). Digital cervical examination shows the cervix to be 4 cm dilated and 100% effaced with the fetal vertex at 0 station. Fetal heart rate monitoring shows a baseline of 140/min, moderate variability, spontaneous accelerations, and no decelerations. An hour later, the patient is noted to have grossly ruptured membranes. Temperature is 37.2 C (99 F), blood pressure is 100/62 mm Hg, and pulse is 100/min. On repeat digital cervical examination, the cervix is 7 cm dilated and 100% effaced with the fetal vertex at +1 station. Fetal heart monitoring is shown in the exhibit.
Which of the following is the most likely cause of this patient's fetal heart rate pattern?

Question

A 30-year-old woman, gravida 1 para 0, at 42 weeks gestation comes to the hospital with regular and painful uterine contractions.  On admission, temperature is 36.1 C (97 F), blood pressure is 110/70 mm Hg, and pulse is 92/min.  Estimated fetal weight is 3.8 kg (8.4 lb).  Digital cervical examination shows the cervix to be 4 cm dilated and 100% effaced with the fetal vertex at 0 station.  Fetal heart rate monitoring shows a baseline of 140/min, moderate variability, spontaneous accelerations, and no decelerations.  An hour later, the patient is noted to have grossly ruptured membranes.  Temperature is 37.2 C (99 F), blood pressure is 100/62 mm Hg, and pulse is 100/min.  On repeat digital cervical examination, the cervix is 7 cm dilated and 100% effaced with the fetal vertex at +1 station.  Fetal heart monitoring is shown in the exhibit. 
Which of the following is the most likely cause of this patient's fetal heart rate pattern?

Quizplus · Accepted Answer

Explanation: 11ec25c8_da2f_1c84_bc81_e702c2745f96_MD0003_00 This patient's fetal heart rate (FHR) tracing has: fetal heart rate (FHR) tracing A normal baseline FHR - defined as 110-160/min Moderate variability - an average amplitude of 6-25/min Variable decelerations - an abrupt decrease in FHR (<30 seconds from onset to nadir) that nadirs at a heart rate ?15/min below the baseline and rapidly returns to baseline. The duration of the entire deceleration is ?15 seconds and <2 minutes. The duration and depth of each deceleration vary and are not always associated with contractions. Variable decelerations are common after rupture of membranes and decrease in amniotic fluid volume, as they can result in umbilical cord compression and occlusion of the umbilical vessels, particularly during contractions. Variable decelerations occur as a response to changes in pressure, as compression and occlusion of the umbilical vessels cause an increase in the fetal systemic vascular resistance and blood pressure, and a reflexive rapid decrease in FHR (ie, variable deceleration). The FHR rapidly returns to baseline as the umbilical cord is decompressed. (Choice A) Fetal head compression causes early decelerations, which have a slow onset (?30 seconds from onset to nadir) and occur symmetrically with contractions. (Choices B and C) Placental abruption and postterm pregnancies are associated with uteroplacental insufficiency and classically cause late (not variable) decelerations. In both cases, the placental surface area is decreased and has suboptimal function, causing transient fetal hypoxemia during contractions. (Choice E) Umbilical cord prolapse is typically associated with an abrupt, prolonged deceleration or bradycardia as the umbilical cord is compressed with no subsequent decompression. Educational objective: Variable decelerations are an abrupt decrease in the fetal heart rate to a nadir followed by a rapid return to baseline and are not always associated with contractions. Variable decelerations are typically due to umbilical cord compression and are common after rupture of membranes. References: 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 30-Year-Old Woman, Gravida 1 Para 0, at 42 Weeks