Tachycardia

The baseline fetal heart rate is an important thing to look at. Two important parts of this are the rate and the variability. Rates above 160 are considered tachycardia. Two of the most common causes of tachycardia are a rise in mothers temperature and drugs taken.

A rise in moms temperature by one degree with increase baby's temperature by around 10 beats per min. Drugs that increase the fetal heart rate are scopalomine, atropine, phenothiazines, terbutaline, ritodrine, or epinephrine.

Other less common causes of tachycardia include fetal hyperthyroidism, fetal anemia, fetal heart failure, and fetal tachyarrhythmias, fetal infection.

Most of the time if an infant has tachycardia, there is no oxygenation problem. Especially if there are other reassuring heart patterns. An exception to this would be if the baby has been deprived of oxygen over a long period of time. Then the heart rate might increase in response to this. There is usually other signs of fetal distress along with this.

References:

Obstetrics: Normal and Problem Pregnancies, 5th ed. Gabbe et al.

Fanaroff and Martin's Neonatal-Perinatal Medicine, 8th ed. Martin et al.