Reproductive · Obstetrics
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Early decelerations are benign findings caused by fetal head compression and mirror the contraction waveform.
Variable decelerations are caused by umbilical cord compression and are defined by an abrupt decrease in fetal heart rate.
Late decelerations indicate uteroplacental insufficiency and require immediate evaluation for fetal hypoxia.
Fetal tachycardia is defined as a baseline heart rate >160 bpm and is most commonly associated with maternal fever or chorioamnionitis.
Category III fetal heart rate tracings are characterized by absent baseline variability with recurrent late decelerations, recurrent variable decelerations, or bradycardia; or a sinusoidal pattern.
Fetal scalp stimulation or vibroacoustic stimulation may be attempted when moderate variability or accelerations are absent, but a 2023 Cochrane review found no clear evidence that it is a safe or effective way to determine fetal well-being.
Resuscitative measures for non-reassuring tracings include maternal lateral positioning, IV fluid bolus, stopping oxytocin, and amnioinfusion; routine maternal oxygen is no longer recommended absent maternal hypoxia.
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A 28-year-old G1P0 female at 39 weeks gestation is in active labor. Her temperature is 101.2°F (38.4°C). Fetal heart rate monitoring shows a baseline of 175 bpm with absent baseline variability and recurrent late decelerations. The patient's cervix is 6 cm dilated. A sinusoidal pattern is noted on the tracing.
What is the most appropriate next step in management?
Expedited cesarean delivery, with intrauterine resuscitation started concurrently
The presence of a Category III tracing (absent variability and sinusoidal pattern) is associated with abnormal fetal acid-base status and requires prompt intrauterine resuscitation together with expedited delivery; a sinusoidal pattern in particular cannot be corrected by resuscitative measures, so operative delivery should proceed expeditiously.
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Etiology / Epidemiology
Caused by uteroplacental insufficiency or umbilical cord compression. High risk in post-term pregnancy, preeclampsia, and fetal growth restriction (FGR).
Clinical Manifestations
Non-reassuring fetal heart rate (FHR) patterns: late decelerations, variable decelerations, or sinusoidal pattern.
Diagnosis
Gold standard is cardiotocography (electronic fetal monitoring). Fetal scalp blood sampling is not generally performed in the United States; acidemia is confirmed after delivery by umbilical artery pH < 7.0.
Treatment
Initial: maternal repositioning, IV fluid bolus, and amnioinfusion for recurrent variables. Stop oxytocin if uterine tachysystole is present.
Prognosis
Risk of hypoxic-ischemic encephalopathy (HIE) and cerebral palsy. Requires emergent cesarean delivery if status fails to improve.
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Epidemiology & Etiology
Nonreassuring fetal status is primarily driven by hypoxia and acidosis during labor. Major risk factors include placental abruption, cord prolapse, and maternal hypotension. It is more common in pregnancies with oligohydramnios due to increased risk of cord compression.
Pertinent Anatomy
The fetoplacental unit relies on adequate perfusion through the spiral arteries. Compression of the umbilical cord disrupts venous return and arterial supply, leading to rapid fetal decompensation.
Pathophysiology
Reduced oxygen delivery triggers a shift to anaerobic metabolism, resulting in lactic acid accumulation. This metabolic acidosis manifests as a loss of fetal heart rate variability. Prolonged hypoxia leads to myocardial depression and sinusoidal pattern, a sign of severe fetal anemia or hypoxia.
Clinical Manifestations
Key findings include late decelerations (uteroplacental insufficiency) and variable decelerations (cord compression). Loss of variability is the most reliable electronic monitoring correlate of fetal compromise, but it is not sensitive - preserved variability does not exclude compromise. A sinusoidal pattern is a red flag for severe fetal anemia or impending fetal death.
Diagnosis
The cardiotocography (CTG) is the primary diagnostic tool. Fetal scalp stimulation may elicit an acceleration, but absence of a response does not reliably establish acidosis and should not by itself drive management. Fetal scalp blood sampling for pH or lactate is performed in many countries but is not generally performed in the United States; acidemia is instead confirmed after birth on an umbilical artery blood gas, where a pH < 7.0 with a base deficit >= 12 mmol/L marks the degree of metabolic acidemia associated with neurologic injury.
Treatment
Initiate intrauterine resuscitation: place patient in left lateral decubitus, administer IV fluid bolus, and consider amnioinfusion; routine supplemental oxygen is not recommended in the absence of maternal hypoxia. Discontinue oxytocin immediately to reduce uterine activity. If non-reassuring patterns persist, perform emergent cesarean section.
Prognosis
Failure to correct hypoxia leads to permanent neurological injury or HIE. Long-term outcomes are linked to the duration of the insult; Apgar scores at 1 and 5 minutes describe the newborn's condition and response to resuscitation but do not predict individual neurologic outcome.
Differential Diagnosis
Fetal sleep cycle: minimal variability with absent accelerations, typically lasting 20-40 minutes and resolving spontaneously
Maternal fever: causes fetal tachycardia
Chorioamnionitis: associated with maternal tachycardia and fetal tachycardia
Cord prolapse: sudden, severe variable decelerations
Placental abruption: painful vaginal bleeding with hypertonic uterus