Reproductive · Obstetrics
The facts most likely to be tested
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 and recurrent late or variable decelerations or sinusoidal pattern.
Fetal scalp stimulation or vibroacoustic stimulation is used to confirm fetal well-being when moderate variability or accelerations are absent.
Resuscitative measures for non-reassuring tracings include maternal lateral positioning, oxygen administration, and IV fluid bolus to improve placental perfusion.
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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?
Immediate cesarean delivery
The presence of a Category III tracing (absent variability and sinusoidal pattern) indicates severe fetal acidemia and requires immediate delivery to prevent fetal demise.
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Etiology / Epidemiology
Caused by uteroplacental insufficiency or umbilical cord compression. High risk in post-term pregnancy, preeclampsia, and IUGR.
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 pH < 7.20 indicates significant acidosis.
Treatment
Initial: maternal repositioning, IV fluid bolus, and oxygen. 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
Fetal distress 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 sensitive indicator of fetal 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 should elicit an acceleration; absence suggests acidosis. Fetal scalp blood gas analysis showing pH < 7.20 is the gold standard for confirming metabolic acidemia.
Treatment
Initiate intrauterine resuscitation: place patient in left lateral decubitus, administer IV fluid bolus, and provide 100% O2 via non-rebreather. 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 are critical prognostic indicators.
Differential Diagnosis
Fetal sleep cycle: normal variability remains
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