Table 2. Multivariable model with and without clustering in all preterm infants.

	Un-clustered			Clustered on familial relation
Variable	Parameter estimate(s)	SE	P-value	Parameter estimate(s)	SE	P-value
Intercept	11.02142	5.68115	0.0525	10.60334	5.63184	0.0598
Maternal race
Asian	-0.15719	0.03980	<0.0001*	-0.15903	0.03946	<0.0001*
Black/African American	0.00283	0.02518	0.9105	0.00383	0.02496	0.8779
Multiple races	-0.09668	0.05513	0.0796	-0.09575	0.05465	0.0799
Other	-0.00151	0.02850	0.9579	-0.00227	0.02826	0.9361
Unknown	-0.02251	0.04450	0.6130	-0.01815	0.04412	0.6808
Maternal first trimester BMI
Underweight	-0.10882	0.05894	0.0650	-0.11562	0.05843	0.0479
Overweight	0.01170	0.01860	0.5294	0.00848	0.01843	0.6456
Obese	0.03154	0.01762	0.0736	0.02956	0.01747	0.0908
Maternal hypertension during pregnancy	-0.00294	0.01909	0.8777	-0.00360	0.01892	0.8492
Preeclampsia	0.00653	0.01859	0.7256	0.00851	0.01843	0.6444
Birth year	-0.00552	0.00282	0.0507	-0.00531	0.00280	0.0578
Multiple(s)	0.02730	0.01593	0.0867	0.03036	0.01579	0.0547
Gestational age (weeks)	0.01599	0.00569	0.0049*	0.01543	0.00564	0.0062*
Birth weight (gr)	-0.00002	0.00003	0.4994	-0.00002	0.00003	0.5108
Birth length (cm)	-0.00022	0.00337	0.9469	0.00008	0.00334	0.9802
Head circumference (cm)	-0.00915	0.00529	0.0837	-0.00894	0.00524	0.0884
TPN	-0.02370	0.02119	0.2634	-0.02204	0.02100	0.2941
Received dextrose	0.03910	0.01818	0.0316*	0.03780	0.01802	0.0361*
Length of birth hospitalization stay (days)	-0.00029	0.00037	0.4378	-0.00029	0.00037	0.4307

Abbreviations: BMI, body mass index; cm, centimeters; gr, grams; SE, standard error; TPN, total parenteral nutrition.

Referent groups: White maternal race, normal maternal first trimester BMI, no hypertension, no preeclampsia, singleton, no TPN, no dextrose.

*p<0.05. P-values were calculated using multivariable linear regression.