Fetal distress or compromise: This is often the most common reason for fetal tachycardia, as the fetus may be experiencing some form of stress, such as cord compression or placental insufficiency, leading to an increase in heart rate.

Fetal anemia: This condition can cause an increase in fetal heart rate due to the decreased oxygen-carrying capacity of the blood.
Fetal infection (e.g., congenital syphilis, toxoplasmosis): Certain infections can cause fetal tachycardia, even in the absence of maternal symptoms.
Fetal cardiac anomalies: Structural heart defects can lead to abnormal heart rhythms, including tachycardia.
Maternal hyperthyroidism: Although maternal tachycardia is not present, uncontrolled hyperthyroidism can still affect the fetus and cause tachycardia.

Fetal arrhythmias (e.g., supraventricular tachycardia): These conditions can be life-threatening if not promptly diagnosed and treated.
Placental abruption: This condition can cause fetal distress and tachycardia, and is a medical emergency.
Umbilical cord prolapse: This is a rare but potentially life-threatening condition that requires immediate attention.

Fetal thyrotoxicosis: This condition is rare but can cause fetal tachycardia due to excessive thyroid hormone production.
Fetal neurologic disorders (e.g., neuroblastoma): Certain neurologic conditions can affect the fetal heart rate, although this is extremely rare.
Maternal substance use or exposure to certain medications: Certain substances or medications can affect the fetus and cause tachycardia, although this would typically be associated with other maternal symptoms.