What does the serum creatinine trend generally do over the first two weeks of life?

In newborns, serum creatinine levels tend to gradually decrease during the first two weeks of life. This decrease is primarily due to the transition from the intrauterine environment to the extrauterine environment, where the kidneys begin to function independently. Creatinine is a waste product generated from muscle metabolism and is typically cleared from the bloodstream by the kidneys.

In newborns, particularly those who are healthy and full-term, an initial high level of creatinine may be observed shortly after birth due to maternal factors. However, as the neonate adapts to life outside the womb and begins to excrete waste products effectively, the serum creatinine levels decrease. This trend is an important aspect of assessing renal function and overall hydration status in newborns.

The other options do not accurately reflect the typical changes in serum creatinine levels during this period. A gradual increase in creatinine would indicate worsening renal function, which is not the case for healthy infants in this age group. Similarly, a constant level or wide fluctuations would suggest instability or ongoing renal issues, which are not expected in normal physiological conditions.