Final answer:
A fetal heart rate of 160 to 170 bpm can be considered normal at 30 weeks gestation, as fetal heart rates can be higher during the later stages of development within the third trimester. A regular fetal heartbeat can be detected as early as six weeks via transvaginal ultrasound.
Step-by-step explanation:
The baseline fetal heart rate (FHR) typically ranges from 110 to 160 beats per minute (bpm), so a baseline FHR of 160 to 170 bpm is slightly higher than the normal range. However, during the third trimester of pregnancy, sometimes as a fetus develops, their heart rate can be slightly higher. Therefore, if a fetus is at 30 weeks of gestation, it is possible that a FHR of 160 to 170 bpm could still be considered a normal variant.
A regular FHR can be detected from around six weeks of gestation with transvaginal ultrasound and by the end of the first trimester with abdominal ultrasound. Tachycardia in a fetus, defined as a FHR above 160 bpm, can occur for various reasons, including maternal fever, dehydration, or fetal activity. It is important to evaluate FHR in the context of the overall clinical picture including mother's health, stage of pregnancy, and fetal activity levels.