Fetal Heart Rate Baseline Abnormalities: Bradycardia
Fetal bradycardia is defined as a baseline fetal heart rate less than 110 beats per minute for at least 10 minutes. Evaluation and management may differ for antenatal and intrapartum fetal bradycardia and depends on gestational age. Fetal heart rate variability provides further information regarding the implications of bradycardia for fetal status. The most common causes of intrapartum bradycardia include poor uterine perfusion, maternal hypotension (e.g. after epidural placement), umbilical cord prolapse or occlusion, rapid fetal descent, tachysystole, placental abruption, or uterine rupture. Antepartum bradycardia may also be due to congenital fetal heart abnormalities or conduction defects like congenital heart block. Moderate fetal heart rate variability is typically reassuring. Minimal fetal heart rate variability can be associated with normal fetal sleep cycles and maternal medication (e.g. opioids, magnesium sulfate). More worrisome causes of reduced variability include decreased fetal oxygenation and fetal neurologic abnormalities like anencephaly.
Management of antenatal fetal bradycardia will depend on gestational age, underlying cause, and overall clinical status of the patient and fetus. When persistent fetal bradycardia with minimal variability is detected remote from term, sonographic examination to assess for structural anomalies and growth restriction should be performed. The use of the M mode for the initial evaluation is also advised. If a cardiac defect or conduction abnormality is suspected, then a fetal echocardiogram is indicated. Maternal laboratory evaluation for collagen vascular disease, specifically SS-A and SS-B antibodies, should be performed if fetal congenital heart block is suspected. Umbilical artery Doppler studies are recommended if fetal growth restriction is present, and antenatal steroids may be warranted if there is likelihood for preterm delivery. Antenatal surveillance is recommended in the third trimester.
Intrapartum fetal bradycardia in the context of a previously normal baseline in labor, particularly when combined with absent or minimal fetal heart rate variability, needs immediate evaluation to identify and correct the underlying cause. Intrauterine resuscitative measures should be initiated, including maternal lateral positioning, maternal oxygen administration, and intravenous fluid bolus administration. If these measures do not resolve bradycardia, especially with absent or minimal variability, digital scalp or vibroacoustic stimulation should be performed and the fetal heart rate monitored for an appropriate response. According to ACOG, if bradycardia with minimal or absent variability or prolonged decelerations or both do not resolve, then prompt delivery is recommended.
American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 106: Intrapartum fetal heart rate monitoring: nomenclature, interpretation, and general management principles. Obstet Gynecol. 2009 Jul;114(1):192-202. doi: 10.1097/AOG.0b013e3181aef106.
American College of Obstetricians and Gynecologists. Practice bulletin no. 116: Management of intrapartum fetal heart rate tracings. Obstet Gynecol. 2010 Nov (Reaffirmed 2017);116(5):1232-40. doi: 10.1097/AOG.0b013e3182004fa9.
Initial Approval: March 2014. Revised July 2017. Reaffirmed January 2019, Reaffirmed September 2020
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