What aspect of renal function is particularly weak in preterm infants?

The glomerular filtration rate (GFR) is particularly weak in preterm infants due to their immature kidney development. In the early stages of life, especially before 32 weeks of gestation, the kidneys haven't fully developed the glomeruli, the structures responsible for filtering blood. As a result, GFR is significantly lower in preterm infants compared to full-term infants. This reduced GFR can lead to difficulties in handling fluid and electrolyte balance, causing preterm infants to be at higher risk for conditions like fluid overload or dehydration if not carefully monitored.

The other options, although they may play roles in renal function, do not represent the most critical limitation in preterm infants. While ureter development and renin secretion are important aspects of renal function, they do not directly compare to the essential role that GFR plays in assessing the kidney's immediate filtering capacity. Fluid regulation is another important function, but it largely hinges on GFR, which is the most notably compromised aspect of renal function in these vulnerable infants.