DOI: https://doi.org/10.21203/rs.3.rs-1375488/v1
Benefits of human milk (HM) are well established in premature infants but might associate slower somatic growth during admission. Body ratios could be used as a proxy for body composition.
This single center, observational, retrospective cohort study compares the effect of predominant HM (group 1, ≥ 75% of HM, n = 151) or not (group 2, < 75%, n = 50) during the first 28 days of life on growth and body ratios at discharge in very preterm infants (VPI).
Weight z-score (-1.63 ± 0.9 vs -0.89 ± 1, p < 0.0001), length z-score (-1.57 ± 1.4 vs -0.95 ± 1.3, p = 0.007) and head circumference (HC) z-score (-0.55 ± 1.3 vs -0.11 ± 1.0, p = 0.025) at discharge were lower in group 1. Fall in z-score in weight from birth to discharge (-1.84 ± 0.8 vs -1.03 ± 0.7, p < 0.0001) and prevalence of postnatal growth failure (PGF) at 36 weeks PMA (73.6% vs 25.6%, p = < 0.0001) were also higher in group 1. Weight/length ratio at discharge was lower in group 1 (4.94 ± 0.6 vs 5.17 ± 0.5, p = 0.022) and the relation of HC z-score compared to weight z-score at discharge was higher in group 1 (1.16 ± 1.0 vs 0.78 ± 0.9, p 0.022).
VPI fed predominantly HM showed slower growth during admission, when compared to those that received a greater amount of formula and had lower markers of adiposity at discharge. Head-to-body proportionality was asymmetric and cephalic growth seemed to be particularly preserved.
There is an increasing interest in the relationship between nutritional status during early infancy and childhood and its influence on adult health [1]. The ideal growth pattern for preterm infants is still unknown [2], although it is mostly accepted that they should follow intrauterine growth rates [3]. However, this goal is not easily attained, resulting in postnatal growth failure (PGF), which has been associated with worse long-term neurocognitive outcomes [4]. Nutritional deficits can contribute up to 50% to PGF [5]. Meeting the nutritional intake recommendations takes time and once achieved they are difficult to maintain throughout hospital stay in preterm infants [5].
The benefits of breast milk are well established [6] and extend to premature and low-birth weight newborns [7], although it requires fortification to fulfill preterm nutrient requirements during early neonatal life in very preterm infants (VPI) [8]. Growth of premature infants fed human milk (HM) might be slower when compared to formula-fed counterparts, but no long-term nutritional compromise has been described [9] and neurodevelopmental outcomes are better [10]. Very preterm infants who received formula achieved recommended intrauterine growth rates but at the expense of increasing adiposity [1], which could relate to worse future metabolic outcomes [11].
The aim of this study was to compare growth outcomes during admission between two groups of VPI with different amount of HM feeding in the first 28 days of life (DOL).
Study design: Single center, observational retrospective cohort study of VPI admitted to a level III intensive care unit. Cohorts were defined by percentage of HM intake (Own’s mother milk -OMM- and/or donor milk -DM) during the first 28 DOL: group 1 ≥ 75% and group 2 < 75%. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the local Ethics Committee (Fundació Sant Joan de Déu Ethics Committee; PIC-20-16).
Patients: Babies born at or before 32 completed weeks of gestational age (GA) were considered eligible. This is a secondary analysis of a previously published cohort [12] of VPI born between 2009 and 2013. Inclusion criteria: Being admitted before 24 h of life and having survived for longer than a week. Exclusion criteria: Major congenital malformations, chromosomal, genetic or metabolic abnormalities, unavailability of clinical records.
Clinical Protocols
Nutritional management of VPI in our unit follows local written guidelines in accordance with international recommendations (see [12–13]).
Study Variables
Actual EN intakes, as reflected on clinical charts. The percentage of HM received over the first 28 DOL was calculated daily for the first 14 days and then averaged with that for day 28. Weight was recorded at admission, day 14 of life, 36 weeks postmenstrual age (PMA) and at discharge and length and head circumference (HC) at birth and discharge. Z-scores for anthropometric parameters were transformed using Intergrowth-21st standards [14–16] until 40 weeks PMA and the WHO standards [17] after that point to allow comparisons at different GA. Postnatal growth failure was defined as a fall in z-score (FZS) greater than 1.34 between two points [2, 18]. Head-to-body growth proportionality was explored as the difference in z-score between HC and weight at a given time point. Weight/length ratio (WLR kg/m) and Body Mass Index (BMI, kg/m2) at birth and discharge and WLR z-scores at discharge, as described by Villar et al. [16], were also calculated as a proxy for body composition.
Statistical Analysis: All data were analyzed with the SPSS® (Statistical Package for Social Sciences, IBM Corp, Armonk, NY, USA) software, v25. Qualitative variables were expressed as frequencies or percentages and quantitative variables as means and standard deviations (SD). Comparisons between both cohorts were performed by chi-square and Student’s t tests as appropriate. Continuous variables without normal distribution were presented as medians (p25, p75) and compared by Mann–Whitney U tests. Differences were considered significant when p-values were < 0.05. Linear and logistic regression analysis were used to assess the effect of HM exposure on growth outcomes after adjustment for potential confounders: GA, CRIB (Clinical Risk Index For Babies) Score, clinical course (expressed as days of mechanical ventilation) and being born before or after DM was available in our unit.
A total of 201 VPI from 256 admitted in the study period were included for analysis (the remaining 55 had exclusion criteria). Of them, 151 were classified in group 1 (≥ 75% of HM) and 50 in group 2 (< 75% of HM). At 28 DOL, patients in group 1 received almost 95% of their EN in the form of OMM but this was only 30% in group 2 (Table 1). Basal characteristics of the sample are summarized in Table 1. Patients in group 1 were of lower GA and birth weight and were more severely ill on admission (higher CRIB score); they also had a more complicated clinical course, but this was not significant after adjusting for GA (Supplementary Table 1). At 28 DOL more infants in group 1 were still receiving PN (13.3% vs 0%, p 0.006) and the volume of enteral intake was consequently lower but averaged over 140 mL/kg/day in both groups (see Table 1).
| Group 1 (n = 151) | Group 2 (n = 50) | p | |
|---|---|---|---|
| Mean ± SD | |||
| Gestational age (weeks) | 28.9 ± 2.3 | 30.6 ± 1.2 | < 0.0001 |
| Birth weight (g) | 1168 ± 351 | 1417 ± 328 | < 0.0001 |
| Median (IQ 25–75) | |||
| CRIB score | 2 (1–4) | 1 (0–2) | < 0.0001 |
| n (%) | |||
| Gender (boy) | 86 (57.0) | 26 (52.0) | 0.623 |
| IUGR | 22 (14.6) | 6 (12.0) | 0.815 |
| SGA | 13 (8.6) | 2 (4.0) | 0.366 |
| Multiple pregnancy | 49 (32.5) | 28 (56.0) | 0.004 |
| Cesarean section | 100 (66.2) | 26 (52.0) | 0.091 |
| Prenatal steroid course (2 doses) | 92 (60.9) | 33 (66.0) | 0.300 |
| Mean ± SD | |||
| Enteral feeding volume (ml/kg/day) Day 28 Discharge | 145.4 ± 44.1 162.2 ± 34.0 | 159.5 ± 19.6 168.8 ± 14.3 | 0.002 0.056 |
| % OMM over 1st 28 days | 94.0 ± 13.9 | 28.2 ± 23.0 | < 0.0001 |
| % DM over 1st 28 days | 4.5 ± 13.6 | 4.0 ± 9.9 | 0.764 |
| CRIB: Clinical Risk Index for Babies, IUGR: Intrauterine growth restriction, SGA: small for gestational age; OMM: Own’s mother milk, DM: Donor milk | |||
Weight, length and HC were lower in group 1 at birth and at 14 DOL, but we found no differences when assessed as z-scores (Supplementary Table 2). There were no differences between groups in HC-to-body proportionality at birth (Table 2). From then on, both weight and weight z-scores (at 28 days, 36 weeks PMA and discharge) (Fig. 1), length z-score and HC z-score at discharge were lower in group 1 (Supplementary table 2). The fall in weight z-score from birth to 36 weeks PMA and from birth to discharge was also higher in group 1 (Table 2), as was the prevalence of PGF at 36 weeks PMA (73.6% vs 25.6%, p = < 0.0001), even after adjusting by GA, CRIB score, days of mechanical ventilation and availability of DM (OR for PGF at 36 weeks: 6.427, 95% CI:2.659–15.534, p < 0.0001). Weight/length ratio at birth and discharge and WLR z-score at discharge were lower in patients from group 1, but WLR increased more in group 1 from birth to discharge, and this was the same for BMI. However, the adjusted analysis indicated that this was due at least partially to the difference in chronological age at discharge, as the group with a higher proportion of HM in the diet had a smaller increase in WLR and BMI (Table 2 and Fig. 2) after adjustment by days of life at measurement and other confounders.
| Change in z-score of anthropometric measurements | ||||||
|---|---|---|---|---|---|---|
| Group 1 (N = 151) | Group 2 (N = 50) | P value | Adjusted ß coefficient (CI 95) | Adjusted P value | ||
| Difference in weight z-score between birth and 36 PMA | -2.13 ± 0.9 | -1.30 ± 0.6 | < 0.0001 | -0.219 (-0.732; -0.202)* | < 0.0001 | |
| Difference in weight z-score between birth and discharge | -1.83 ± 0.8 | -1.03 ± 0.7 | < 0.0001 | -0.240 (0.701; 0.253)* | < 0.0001 | |
| Difference in length z-score between birth and discharge | -1.41 ± 1.1 | -0.62 ± 1.0 | < 0.0001 | -0,162 (-0.757; -0.094)* | 0.012 | |
| Difference in HC z-score between birth and discharge | -0.26 ± 1.1 | 0.05 ± 0.99 | 0.070 | -0.126 (-0.638; 0.047)* | 0.091 | |
| Body ratios | ||||||
| Group 1 (N = 151) | Group 2 (N = 50) | Adjusted ß coefficient (CI 95) | Adjusted P value | |||
| WLR | ||||||
| At birth (kg/m) | 3.09 ± 0.7 | 3.59 ± 0.6 | < 0.0001 | - | - | |
| At discharge (kg/m) | 4.94 ± 0.6 | 5.17 ± 0.5 | 0.022 | -0.257 (-0.527; -0.203)* | < 0.0001 | |
| Z-score at discharge | -1.83 ± 0.9 | -1.11 ± 0.8 | < 0.0001 | -0.260 (-0.831; -0.277)* | < 0.0001 | |
| Difference between birth and discharge | 1.85 ± 0.90 | 1.58 ± 0.71 | 0.032 | -0.153 (-0.440; -0.164)* | < 0.0001 | |
| BMI | ||||||
| At birth (kg/m2) | 8.25 ± 1.4 | 9.17 ± 1.2 | < 0.0001 | - | - | |
| At discharge (kg/m2) | 10.99 ± 1.2 | 11.41 ± 0.8 | < 0.008 | -0.286 (-1.049; -0.423)* | < 0.0001 | |
| Difference between birth and discharge | 2.75 ± 1.8 | 2.23 ± 1.4 | 0.074 | -0.112 (-0.865; -0.033)* | < 0.035 | |
| Difference in z-score between HC and weight (HC z score- weight z score) | ||||||
| At birth | -0.40 ± 0.82 | -0.30 ± 0.64 | 0.404 | - | - | |
| At discharge | 1.16 ± 1.0 | 0.78 ± 0.9 | 0.022 | 0.103* (-0.067; 0.515) | 0.130 | |
| *Results adjusted by GA, availability of donor milk, CRIB score, days of mechanical ventilation and days of life at discharge. Abbreviations: PMA postmenstrual age, HC head circumference, WLR weight/length ratio. | ||||||
With regard to HC-to-body proportionality, weight and HC z-scores were similar to each other at birth in both groups (Supplementary Table 2), but HC was better preserved from birth to discharge than weight z-score, particularly in group 1 (Fig. 2, Table 2). This trend disappeared after adjustment by confounders, specially postnatal age (Table 2).
Our results show that in a cohort of VPI fed predominantly HM with standard fortification, those receiving more HM during their first 28 DOL had slower postnatal growth during admission than those who were on PF. In the HM-fed VPI group, both weight and weight z-score at 36 weeks PMA and at discharge were lower, while FZS in weight from birth to 36 weeks GA and to discharge and the percentage of patients showing PGF were higher, as previously reported [9, 19, 20]. In an adjusted analysis, increase in WLR and BMI from birth to discharge was smaller in predominantly HM-fed infants, while head growth showed a trend to be better preserved.
Exclusive HM feeding has been associated with reduced mortality and a decrease in morbidity of VPI [21]. However, artificial formula results in higher rates of weight gain and linear growth than HM due to its greater amount of nutrients, particularly in the case of DM, which may be further compromised by pasteurization [8]. Human milk only provides about 60% of the protein requirements when fed in adequate amounts to sustain energy requirements in preterm infants [1], so that an insufficient protein supply through standard fortification could lead to a low protein-energy ratio resulting in deficient lean mass retention [8]. This is in line with the findings of a study using whole-body MRI for the assessment of body composition [22], but contrary to a recent literature review which suggests that HM feeding in preterm infants, although related to a slower weight gain than formula feeding, is associated with a better promotion of fat free mass (FFM) deposition [20]. Other potential contributors to delayed growth of HM-fed infants in our cohort are feeding volumes at 28 DOL, which did not reach 160 ml/kg/day (lower limit of the recommendation for a stable growing preterm infant) [23], and standard HM fortification. Recent recommendations of the European Milk Bank Association recognized that “Standard Fortification” can fall short in supplying sufficient protein for some VPI and encouraged the use of “Individualized Fortification” to optimize nutrient intake [24], although this practice is not yet widespread.
Apart from measuring growth in terms of increase in weight or length, the quality of body composition is also relevant in relation to future health outcomes. Several studies have shown that body composition of preterm infants when they reach term equivalent age is different from that of their term newborns counterparts [25], with a higher percentage of total body fat [16, 25, 26].
Assessment of body composition in preterm infants is challenging, as most methods used in research settings are difficult to implement into daily clinical practice [27]. Alternative options include using skinfolds or anthropometric ratios (WLR, BMI or ponderal index) to predict body composition [25, 27]. Although at birth the WLR seems to primarily correlate with FFM (R2 0.92) [16], changes in WLR and BMI better reflect an increase in adiposity after the first weeks or months of life, once the postnatal deposition of body fat begins, at least in term infants [28]. Our study showed that preterm infants fed ≥ 75% HM (Group 1) had a lower WLR at birth and discharge than infants in group 2, but a higher increase in WLR and BMI from birth to discharge. This seemed to result from the confounding effect of a higher chronological age, as the adjusted analysis pointed to a protective effect of HM in the sense of a slower deposition of fat mass (FM) as assessed by the increase in body ratios (WLR and BMI). A similar effect on BMI increase, particularly in association with formula protein intake has also been reported in healthy infants [29].
Another difference in the pattern of growth between groups refers to proportionality between head and whole body growth. Head circumference z-score from birth to discharge decreased in both groups, with no difference between them. However, the magnitude of change of HC z-score from birth to discharge tended to be smaller in group 1 with respect to the change in body weight z-score, which suggests that head growth could be somehow prioritized. This could be an explanation of why, in spite of slower weight gain, neurodevelopmental outcomes are better in preterm infants fed OMM [10], although differential patterns of body growth are rarely reflected in the literature, making interpretation difficult.
We have analyzed growth outcomes in a cohort of VPIs in relation to preferential HM or formula-feeding. Although we only considered the source of nutrition up to 28 days, it was recorded in detail (daily for the 1st 14 DOL and then for day 28) at a time point that has been shown to predict EN at discharge [30]. One of the limitations of our study, inherent to the retrospective design, is the available sample size and the baseline differences between groups, which we tried to address by adjusting for potential confounders, as GA and severity of clinical course. There is a moderately high rate of breastfeeding in our sample, and the proportion of DM consumed was under 5% in both groups, so these results reflect mostly OMM. Lastly, we lack follow up data to see the impact of these differences later on.
Our data support the evidence suggesting that current HM feeding practices for preterm infants in neonatal units, while protecting them from morbidity, result in slower growth when compared to formula. However, our focus on body ratios and proportionality suggests it may particularly limit fat deposition when compared with formula, and preserve cephalic growth, which could be the basis for previously described better cardiovascular, metabolic and neurodevelopmental outcomes in HM-fed preterm infants [9]. Strategies aimed at supporting growth while taking into account body composition and proportionality should be implemented and regularly audited in order to minimize PGF while using HM.
body mass index
donor milk
days of life
enteral nutrition
fat-free mass
fall in z-score
gestational age
head circumference
human milk
own’s mother milk
preterm formula
postnatal growth Failure
postmenstrual age
parenteral nutrition
standard deviation
very preterm infants
weight/length ratio
Ethics approval and consent to participate: The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the local Ethics Committee (Fundació Sant Joan de Déu Ethics Committee; PIC-20-16). Due to the retrospective nature of the study and the use of anonymized data routinely collected for auditing and quality of care purposes, a waiver of consent was sought and granted by the local Ethics Committee (Fundació Sant Joan de Déu Ethics Committee: PIC-20-16).
Consent to publish: Not applicable
Availability of data and material: Data analyzed in this study is available from the corresponding author upon request.
Competing interest: No competing financial interests exist.
Funding: IIP and MIR received financial support from the National R+D+I Plan (PI17/00107) of the ISCIII (Subdirección General de Evaluación y Fomento de la Investigación Sanitaria), wich was cofounded by the European Union Regional Development Fund (FEDER).
Author Contributions: SSG and DCV reviewed the cases and collected the data. SSG collaborated in data analysis and reviewed the bibliography, prepared and wrote the first draft of this paper, and coordinated manuscript revisions and submission. MIR and IIP, planned and design the study, revised the methodology and led the statistical analysis, as well as reviewing and editing the manuscript. All the authors have seen and approved the final version.
Acknowledgements: We would like to thank all the families that agreed to participate in the study and all the members of the Neonatal Unit.