Statistical analyses
We previously [Infants were classified into three categories based on the administration of parenteral lipids during the first four weeks of life. Per each infant and day, the amount of administered parenteral lipids was standardized into a parenteral lipid standard deviation score (PNSDS) using the studied population’s daily means and standard deviations. Daily PNSDS were then flagged with higher intake if they were greater than 0, and the percentage of follow-up time on this higher intake was calculated (% time with PNSDS>0). Finally, % time with PNSDS>0 was categorized into three categories for analyses: ≤25th percentile, 25th-75th percentile, and ≥75th percentile. The amounts of administered parenteral lipids and their relationship to serum phospholipids were then described for the three categories.Statistical analyses were performed using IBM SPSS Statistics version 27 (IBM Corp, Armonk, NY, USA) and SAS software version 9.4 (SAS Institute Inc., Cary, NC, USA). Rstudio Version 1.2.5033, R Version 4.0.4 [For differences in patient characteristic distribution between the two randomized groups, Fisher’s exact test was used for dichotomous variables and Mann–Whitney U-test for continuous variables. Test for trend between three categories of parenteral lipids was performed using Mantel–Haenszel Chi-Square test for dichotomous variables, Chi-Square test for non-ordered categorical variables, and Jonckheere–Terpstra test for continuous variables. Unadjusted pairwise Wilcoxon signed-rank test was used to compare fatty acid levels in cord blood with later postnatal time points.Longitudinal fatty acids were analyzed using mixed models for repeated measures data with normal distribution, adjusting for within-infant correlation, and modeling age in days with the spline function. Fixed knots at 0.02, 0.05, 0.1, 0.3, and 0.5 fractions of time resulted in lower Akaike’s Information Criterion. The models included treatment arm, age (spline function), and interaction between intervention and age, and were adjusted for center, gestational age at birth, birth weight including interaction with age, and sex. Diagnostic plots of residuals were reviewed and found satisfactory. The difference between the estimated mean values of fatty acids for the two treatment arms was computed, adjusting the confidence intervals (CIs) and p-values for multiple testing using the Scheffe-Holm method. Similar models adjusted for GA at birth, birth weight, and both variables, including interaction with PNA and sex, were also performed for the three categories of PNSDS (≤25th, 25th-75th, ≥75th percentile). Statistical analyses were limited to the first 13 weeks to have a similar distribution of gestational ages at birth across the analysis period. All tests were two-sided and evaluated at a 0.05 significance level.