Final answer:
A fetal heart rate typically becomes reactive around the beginning of the third trimester, indicating healthy responsiveness to stimuli. Heartbeats can be detected as early as 5 to 6 weeks of gestation, and heart rate is an important part of the Apgar score immediately after birth.
Step-by-step explanation:
The fetal heart rate becomes reactive, typically around the beginning of the third trimester, when the fetus begins to respond to environmental stimuli. This is characterized by an increase in heart rate in response to movement. The presence of a reactive heart rate is a positive sign indicating that the fetus is developing normally and is responsive to changes in its environment. The ability to detect a regular heartbeat can be found in earlier stages of development, usually around the 5th to 6th week of gestation, although it becomes easier to detect as the fetus grows.
Immediately following birth, the assessment of the newborn's heart rate is an important aspect of the Apgar score, which is a quick test performed on a baby at 1 minute and 5 minutes after birth. This test measures several criteria, including heart rate, to determine how well the baby is doing outside the womb. An Apgar score lower than 7 may indicate that medical assistance is required. A regular and adequate heart rate post-birth is an essential sign of a healthy transition from fetal to newborn life.