Supplemental Table S1. Serum Creatinine Nadir Value and Timing by Exact Gestational Age Week 	
Exact GA (weeks)	N Infants in GA Week	Nadir SCr, mg/dL
(Week Reached, N)	Nadir SCr Excl. Least-Precise Site, mg/dL (Week Reached, N)	
22	147	0.22 (wk 18, n=59)	0.22 (wk 18, n=59)	
23	705	0.22 (wk 24, n=162)	0.22 (wk 24, n=159)	
24	1007	0.21 (wk 19, n=316)	0.21 (wk 19, n=298)	
25	1044	0.21 (wk 21, n=229)	0.21 (wk 21, n=218)	
26	1014	0.21 (wk 20, n=167)	0.21 (wk 20, n=158)	
27	902	0.21 (wk 19, n=154)	0.21 (wk 19, n=149)	
28	860	0.20 (wk 18, n=101)	0.20 (wk 18, n=97)	
29	806	0.21 (wk 15, n=109)	0.21 (wk 15, n=103)	
30	832	0.20 (wk 23, n=35)	0.20 (wk 24, n=26)	
31	878	0.20 (wk 15, n=79)	0.20 (wk 23, n=28)	
32	1062	0.20 (wk 22, n=43)	0.20 (wk 24, n=30)	
33	1133	0.20 (wk 20, n=51)	0.20 (wk 20, n=50)	
34	1774	0.21 (wk 14, n=123)	0.21 (wk 14, n=120)	
35	1900	0.23 (wk 10, n=159)	0.23 (wk 9, n=162)	
36	2672	0.20 (wk 18, n=78)	0.20 (wk 18, n=73)	
37	4237	0.20 (wk 22, n=64)	0.20 (wk 19, n=77)	
38	3780	0.19 (wk 24, n=36)	0.20 (wk 24, n=35)	
39	5665	0.22 (wk 21, n=62)	0.22 (wk 21, n=60)	
40	2993	0.20 (wk 20, n=21)	0.20 (wk 20, n=20)	
For each exact gestational age (GA) week, the minimum observed median serum creatinine value ("nadir") and the week of life at which it occurred, calculated using all sites and after excluding one site with markedly coarser measurement precision (see Limitations). GA weeks 41 and 42 are excluded due to extremely small samples (n=1 infant contributing to the nadir estimate at each). Although the nadir value was reasonably consistent across GA (approximately 0.20-0.23 mg/dL) and stable to site exclusion, the week at which this nadir was reached varied non-monotonically across GA and was sensitive to site exclusion, even in adequately powered strata. This timing metric should be interpreted as exploratory only and not as a precise or clinically actionable estimate.