Final answer:
The Apgar score is an assessment which includes heart rate as one of the five criteria for newborn evaluation. Fetal heart rate is not a standalone category with tiers but is assigned a score under the Apgar system, part of the overall newborn assessment with a score of 0, 1, or 2. A normal fetal heartbeat can be detected as early as the 6th week of pregnancy.
Step-by-step explanation:
The question appears to concern the classification of fetal heart rates (FHR) by the Apgar score, which is a quick test performed on a newborn shortly after birth. However, the specific question about 'tiers' used to classify fetal heart rate seems to be based on an oversight, as fetal heart rate is but one component of the Apgar score. The Apgar score assesses five criteria: skin color, heart rate, reflex, muscle tone, and respiration. The fetal heart rate is critical in this assessment and is scored 0, 1, or 2, with a score of 2 indicating a healthy heart rate of more than 100 beats per minute (bpm), 1 for a heart rate lower than 100 bpm, and 0 for no heart rate. A total Apgar score below 7 at 5 minutes may lead to the newborn receiving medical assistance, and a score below 5 indicates a situation that requires emergent intervention.
Regarding the development of the fetal heartbeat, in the early stages of pregnancy, a regular fetal heartbeat can be detected through ultrasound as soon as the 6th week of gestation. The resting heart rate of newborns can be approximately 120 bpm and changes throughout life, although heart rates may vary considerably due to several factors such as exercise, fitness levels, and age.