Data were available for a total of 78 preterm infants and 256 term infants. Preterm infants were born at mean (SD) of 28(2.2) weeks gestational age and term infants had a mean (SD) gestational age of 39 (2.2) weeks, with the preterm infants being statistically smaller than the term infants at all study assessments. The majority of all infants in all groups received breast milk. Further demographic details are provided in Table 1.
Table 1: Clinical Characteristics.
Characteristics
|
Preterm Cohort
|
Term Cohort
|
PEF
(n=67)
|
PAT
(n=38)
|
Birth
(n= 82)
|
2 weeks
post delivery
(n=93)
|
6 weeks
post delivery
(n=81)
|
Gestational Age at Birth
(weeks)
|
28.00
(2.2)
|
28.00
(2.3)
|
39.77
(1.2)
|
39.77
(1.2)
|
39.88
(1.1)
|
Age at assessment
|
4 (2)
weeks
|
10 (3)
weeks
|
5 (2)
days
|
2 (1)
weeks
|
6 (0)
weeks
|
Sex
|
♂: 28 (40%)
♀: 42 (60%)
|
♂:20 (53%)
♀:18 (47%)
|
♂:39 (47%)
♀:43 (53%)
|
♂:39 (42%)
♀:54 (58%)
|
♂:33 (41%)
♀:48 (59%)
|
Weight at birth (g)
|
1117 (407)
|
1125 (389)
|
3605 (505)
|
3657 (487)
|
3680 (537)
|
Weight SDS at birth
|
-0.34 (1.25)
|
-0.37 (1.31)
|
0.41 (0.92)
|
0.51 (0.89)
|
0.50 (1.08)
|
Weight at assessment (g)
|
1456 (422)
|
2488 (555)
|
3593 (492)
|
3981 (612)
|
4866 (115)
|
Weight SDS at assessment
|
-1.81 (2.16)
|
-1.61 (1.39)
|
0.046 (0.87)
|
0.13 (0.99)
|
0.57 (1.18)
|
Feeding type
|
BM 42 (60%)
FM 7 (10%)
MF 18 (27%)
|
BM 22 (58%)
FM 10 (26%)
MF 6 (16%)
|
BM 71 (87%)
FM 4 (5%)
MF 6 (7%)
NA 1(1%)
|
BM 81 (87%)
FM 2 (2%)
MF 10 (11%)
|
BM 64 (79%)
FM 4 (5%)
MF 13 (16%)
|
Abbreviation: PEF –Preterm established on enteral feeding, PAT – Preterm at Term, BM – Breast milk, FM – Formula Milk, MF – Mixed Feeding. Data is given as n (%) or mean (SD) NA – not available
Desaturase Activity in Preterm Infants
As shown in Figure 1 there were significant differences in specific DA between the two study time points. FADS1(TG), FADS2(PC) and SCD1 levels were lower at term corrected age, compared to when preterm infants were first established on enteral feeds. In contrast FADS1(PC) and FADS2(TG) levels were higher at term corrected age.
Figure 1 Box plots of the lipid ratios, represent desaturase enzyme activity in preterm infants at two time points; preterm on establishment of enteral feeding (PEF) and preterm at term corrected age (PAT). The boxes indicate 25th -75th percentile and a median line.
Values are in mean (SD). Abbreviation: PEF-Preterm on established enteral feeding, PAT – preterm at Term, SCD 1- stearoyl-COA desaturase, FADS 1- fatty acid desaturases 1, FADS 2- fatty acid desaturases 1, PC-phosphatidylcholine, TG-triglyceride. P values were obtained by the Mann-Whitney U test. *p< .05, **p< .001
Comparison of DA between preterm and term infants
Table 2a show that PEF infants had similar SCD1 with term infants at birth, but significantly different from term infants at 2- and 6-weeks postnatal age (p=0.001). At term corrected age (>37 weeks PMA), SCD1 was statistically lower than term infants at birth (Table 2b). FADS1 activity was consistently lower in preterm infants at both time points compared to term infants from birth to 6 weeks of age.
Table 2a: Lipid ratios among preterm infants on establishment of enteral feeds (PEF) and term infants
VARIABLES
|
PEF
|
TAB
|
Z score
|
p
|
T2W
|
Z score
|
p
|
T6W
|
Z score
|
p
|
SCD1
|
0.43 (0.21)
|
0.43
(0.17)
|
-0.92
|
0.36
|
0.27
(0.11)
|
-5.88
|
**
|
0.24
(0.13)
|
-6.59
|
**
|
FADS1
(PC)
|
3.08 (1.22)
|
6.05
(3.87)
|
-7.11
|
**
|
3.88
(3.36)
|
-3.21
|
*
|
3.59
(1.05)
|
-3.98
|
**
|
FADS1
(TG)
|
1.23 (0.32)
|
2.21
(1.06)
|
-7.64
|
**
|
1.39
(0.34)
|
-3.09
|
*
|
1.28
(0.26)
|
-1.37
|
0.17
|
FADS2
(PC)
|
0.53 (0.12)
|
0.59
(0.13)
|
-4.11
|
**
|
0.46
(0.07)
|
-4.36
|
**
|
0.39
(0.05)
|
-8.81
|
**
|
FADS2
(TG)
|
0.72 (0.16)
|
0.33
(0.25)
|
-9.04
|
**
|
0.39
(0.21)
|
-8.66
|
**
|
0.52
(0.24)
|
-6.13
|
**
|
Table 2a The comparison of lipid ratios among PEF and term infants at birth, 2 weeks, and 6 weeks. Lipid ratios were presented as mean (SD), but for statistical significance, the mean ranks among the groups were compared. Abbreviation: PEF – preterm after establishing enteral feeding, SCD 1- stearoyl-COA desaturase, FADS 1- fatty acid desaturases 1, FADS 2- fatty acid desaturases 1, PC-phosphatidylcholine, TG-triglyceride. P values were obtained by Kruskal Wallis Test and Post Hoc by Mann Whitney U-Test with Bonferroni adjustment at p<.0001, *p<.05, *p<.001
Table 2b: Lipid ratios among preterm at term (PAT) and term infants
VARIABLES
|
PAT
|
TAB
|
Z score
|
p
|
T2W
|
Z score
|
p
|
T6W
|
Z score
|
p
|
SCD1
|
0.32 (0.16)
|
0.43
(0.17)
|
-3.84
|
**
|
0.27
(0.11)
|
-1.05
|
0.296
|
0.24
(0.13)
|
-2.71
|
*
|
FADS1
(PC)
|
3.15 (0.94)
|
6.05
(3.87)
|
-5.40
|
**
|
3.88
(3.36)
|
-1.75
|
0.081
|
3.59
(1.05)
|
-2.22
|
*
|
FADS1
(TG)
|
1.13 (0.43)
|
2.21
(1.06)
|
-7.08
|
**
|
1.39
(0.34)
|
-4.74
|
**
|
1.28
(0.26)
|
-3.80
|
**
|
FADS2
(PC)
|
0.46 (0.15)
|
0.59
(0.13)
|
-5.86
|
**
|
0.46
(0.07)
|
-1.93
|
0.054
|
0.39
(0.05)
|
-3.19
|
*
|
FADS2
(TG)
|
0.83 (0.20)
|
0.33
(0.25)
|
-8.03
|
**
|
0.39
(0.21)
|
-8.01
|
**
|
0.52
(0.24)
|
-6.57
|
**
|
Table 2b Comparison of lipid ratios among PAT and term infants at birth, 2 weeks, and 6 weeks. Lipid ratios were presented as mean (SD), but for statistical significance, the mean ranks among the groups were compared. Abbreviation: PAT – preterm at term, SCD 1- stearoyl-COA desaturase, FADS 1- fatty acid desaturases 1, FADS 2- fatty acid desaturases 1, PC-phosphatidylcholine, TG-triglyceride. P values were obtained by Kruskal Wallis Test, and Post Hoc by Mann Whitney U-Test with Bonferroni adjustment at p<.0001, *p<.05, *p<.001.
FADS2 in preterm infants was generally higher than term infants at 2 and 6 weeks and especially FADS2(TG) was significantly higher than term infants, at all time points. Similarly in PEF infants’ FADS2(PC) activity was higher than that of term infants at 2 and 6 weeks (p<0.001). Although FADS2(PC) activity was lower in PAT compared to term infants at birth, it was higher than term infants at 6 weeks (p<0.03).
Desaturase enzyme activity in the cohorts over time is shown in Figure 2, with preterm infant results plotted in duplicate to show levels in relation to postmenstrual (32 and 38 weeks) and postnatal age (4 and 10 weeks). This shows that although there were significant differences in DA levels at specific time points for most of the DA, the trajectories of activity over time were similar in the two cohorts. The exception to this was the contradict trajectory in FADS1(PC) between the cohorts and a rapid fall in FADS1 activity from birth to 2 weeks postnatal age in the term cohort.