Final answer:
The highest concentration of hCG is found in the morning because the hormone accumulates overnight when the body does not excrete fluids, leading to higher levels in the urine which is useful for pregnancy testing and in certain fertility treatments.
Step-by-step explanation:
The time of day with the highest concentration of human chorionic gonadotropin (hCG) present is the morning. This hormone is known to be at its peak levels in the morning because it accumulates during sleep when the body is not excreting fluids. hCG is often measured in the morning by pregnancy tests to provide the most accurate results, as its concentration in urine is the highest after a night's sleep. The importance of hCG levels can also be linked to its use in fertility treatments, where it is injected before the retrieval of eggs, indicating its significant role in reproductive processes.