Why are hCG levels higher in the morning?

hCG (human chorionic gonadotropin) levels are typically higher in the morning due to the body's natural diurnal rhythm, which causes hormone concentrations to fluctuate throughout the day. Overnight, urine becomes more concentrated as the body retains fluids during sleep, leading to higher detectable levels of hCG in the morning. This is why many pregnancy tests recommend testing first thing in the morning for the most accurate results.