From the Guidelines
Fetal tachycardia during labor is most commonly caused by maternal fever or infection, fetal anemia, and acute fetal hypoxia, which can be identified and managed using the DR C BRAVADO mnemonic for interpretation of continuous electronic fetal monitoring 1. The causes of fetal tachycardia during labor can be multifactorial and include:
- Maternal fever or infection, which can directly increase the fetal heart rate as the fetus responds to the elevated maternal temperature
- Fetal anemia, whether from Rh incompatibility, fetomaternal hemorrhage, or other causes, can lead to compensatory tachycardia as the fetus attempts to maintain oxygen delivery
- Acute fetal hypoxia initially causes tachycardia before potentially progressing to bradycardia if prolonged
- Certain medications, such as anticholinergics, beta-sympathomimetics like terbutaline, and parasympatholytics, can trigger fetal tachycardia
- Maternal hyperthyroidism may transfer excess thyroid hormone to the fetus, increasing heart rate
- Other causes include maternal dehydration, maternal anxiety, premature rupture of membranes, placental abruption, and fetal cardiac arrhythmias When fetal tachycardia is detected, immediate evaluation of maternal vital signs, particularly temperature, is essential, along with consideration of potential underlying causes to guide appropriate management during labor, as outlined in the DR C BRAVADO mnemonic 1. It is also important to note that some cases of fetal tachycardia may be related to nonimmune hydrops fetalis (NIHF), which can be caused by various factors, including cardiovascular, chromosomal, hematologic, infectious, and thoracic abnormalities, as well as twin-twin transfusion, urinary tract abnormalities, and lymphatic dysplasia 1. However, the most recent and highest quality study on fetal monitoring recommends using the DR C BRAVADO mnemonic for interpretation of continuous electronic fetal monitoring 1.
From the Research
Causes of Fetal Tachycardia
- Fetal tachycardia can be caused by various factors, including maternal fever and chorioamnionitis 2
- Supraventricular tachycardia (SVT) is a rare but potential cause of fetal tachycardia, which may be missed as a diagnosis, leading to suboptimal management 3
- Fetal arrhythmias, including tachyarrhythmia and bradyarrhythmia, can also cause fetal tachycardia 4
- Maternal tachycardia during the second stage of labor can be a potential risk factor for fetal monitoring confusion, and may be associated with fetal tachycardia 5
Association with Maternal and Neonatal Morbidity
- Fetal tachycardia has been associated with increased risk of neonatal complications, such as respiratory distress syndrome (RDS), asphyxia, and meconium aspiration 6
- Maternal fever and chorioamnionitis have been linked to fetal tachycardia, and may increase the risk of perinatal morbidity 2
- Fetal tachycardia has also been associated with higher odds of arterial cord pH <7.2 and base deficit ≥12, indicating fetal acidemia 2
Diagnosis and Management
- Fetal tachycardia can be diagnosed using cardiotocography and Doppler technology 4
- Transplacental therapy, such as digoxin, sotalol, and flecainide, can be effective in managing fetal tachycardia, particularly in cases of supraventricular tachycardia 4
- Antenatal detection of fetal SVT is important, as it can allow anticipation and prevention of neonatal SVT, which is potentially life-threatening if not detected and treated promptly 3