Final answer:
Gestation, or the length of time of development from conception to birth, is determined by various factors. This can be estimated through methods such as ultrasound and hormone level measurement.
Step-by-step explanation:
Gestation, or the length of time of development from conception to birth, is determined by various factors. In humans, the gestation period is typically 266 days. The age of a fetus can be estimated through methods such as ultrasound, which measures the size and development of the fetus. Additionally, the measurement of hormone levels, such as human beta chorionic gonadotropin (B-HCG), can be used to determine the stage of pregnancy.