OBJECTIVES

To assess effects of calcium or phosphorous supplementation compared with no supplementation in human milk-fed preterm or low birth weight infants.

METHODS

Data sources include Cochrane Central Register of Controlled Trials, Medline and Embase. We included Randomized controlled trials (RCTs) and non-randomized trials (quasi-randomized).

RESULTS

Three studies (4 reports; 162 infants) were included. At latest follow-up (38 weeks), there was reduction in osteopenia (3 studies, 159 participants, relative risk 0.68, 95% confidence interval [CI] 0.46–0.99). At latest follow-up (6 weeks), there was no effect on weight (1 study, 40 participants, mean difference [MD] 138.50 g, 95% CI −82.16 to 359.16); length (1 study, 40 participants, MD 0.77 cm, 95% CI −0.93 to 2.47); and head circumference (1 study, 40 participants, MD 0.33 cm, 95% CI −0.30 to 0.96). At latest follow-up, there was no effect on alkaline phosphatase (55 weeks) (2 studies, 122 participants, MD −126.11 IU/L, 95% CI −298.5 to 46.27, I2 = 73.4%); serum calcium (6 weeks) (1 study, 40 participants, MD 0.54 mg/dL, 95% CI −0.19 to 1.27); and serum phosphorus (6 weeks) (1 study, 40 participants, MD 0.07 mg/dL, 95% CI −0.22 to 0.36). The certainty of evidence ranged from very low to low. No studies reported on mortality and neurodevelopment outcomes.

CONCLUSIONS

The evidence is insufficient to determine whether enteral supplementation with calcium or phosphorus for preterm or low birth weight infants who are fed mother's own milk or donor human milk is associated with benefit or harm.

Many preterm and low birth weight (LBW) infants are born with low stores of calcium and phosphorous1,2 ; and human milk may not be sufficient for adequate postnatal skeletal growth and development in these infants.35  Preterm and LBW infants are at risk for hypophosphatemia, poor bone mineralization and elevated alkaline phosphatase activity, fractures, and lower than expected growth rates.68 

A Cochrane systematic review of calcium or phosphorus supplementation of human milk for preterm hospitalized infants was published in 2017.9  However, there have been no systematic reviews of calcium or phosphorous supplementation for preterm or LBW infants in either hospital or community settings since this time. The World Health Organization (WHO) currently recommends calcium and phosphorous supplements for very LBW (<1.5 kg) infants.10 

The primary objective of this review was to assess the effect of calcium or phosphorus supplementation during infancy compared with no supplementation on mortality, morbidity, growth, and neurodevelopmental outcomes in preterm or LBW infants who are fed mother's own milk or donor human milk. The secondary objectives were to determine the optimal time of initiation, dose and duration of calcium, and phosphorus supplementation during infancy.

The protocol for this review was registered in PROSPERO (PROSPERO 2021 CRD42021238802).11 

We included randomized controlled trials or nonrandomized trials (quasi-randomized) in which individual preterm (<37 weeks’ gestational age) or LBW (birth weight <2.5 kg) infants fed mother's own milk or donor human milk were either allocated to receive enteral calcium or phosphorus supplementation and compared with a control group (placebo or no drug); allocated to different regimens of calcium or phosphorus supplementation (in terms of dosage, duration, and timing of initiation). Studies in which enteral calcium and phosphorus supplementation was provided for treatment of any disease were excluded.

A comprehensive search (Appendix 1) was conducted in the Cochrane Central Register of Controlled Trials (2016, Issue 3) in the Cochrane Library via the Cochrane Register of Studies Online,12  Medline via PubMed,13  and Embase14  from inception to March 24, 2021. There were no language restrictions.

Two review authors (T.S.C., M.K.) independently screened the titles and abstracts to identify potentially relevant citations. The authors then independently assessed the eligibility of the studies in accordance with the specified inclusion criteria. Any disagreements were resolved by discussion and, if necessary, by consulting a third review author (R.C.). The reference lists of articles selected for inclusion in this review were searched to identify additional relevant articles. Screening and full text selection were managed using the Web-based software Covidence.15  Following standard methods described in the Cochrane Handbook for Systematic Reviews of Interventions,16  2 review authors (T.S.C., M.K.) independently extracted data using a data abstraction form integrated with a modified version of the Cochrane Effective Practice and Organization of Care Group data collection checklist (2017).17 

Two review authors (T.S.C., M.K.) independently assessed the risk of bias (ROB) of all included trials using the Revised Cochrane ROB tool for randomized trials (ROB 2) and ROB in nonrandomized studies of interventions.18  In case of discrepancies among their judgments and inability to reach consensus, a third review author was consulted. We planned to use funnel plots and Egger’s test to assess publication bias in outcomes with >10 studies.19 

The outcomes for this review were categorized into primary and secondary (Appendix 2). For each outcome, studies were pooled at the latest follow-up if >1 study were available. If single study reported an outcome, individual study effect sizes was reported. The unit of analysis was the infant.

We used relative risk (RR) and mean difference (MD) as our outcome estimate measures for categorical and continuous outcomes, respectively, and recorded them as provided in the article. We used adjusted RR or MD where studies reported and estimated unadjusted RR or MD where adjusted RR or MD was not presented. To estimate the effect of calcium or phosphorus supplementation on prespecified outcomes, we conducted a meta-analysis using “meta” command in Stata v1620 ; pooled adjusted and unadjusted RR or MD together and reported the pooled RR or MD and corresponding 95% confidence (CI).16 

We used a fixed-effect meta-analysis (inverse variance method) to combine data when it was reasonable to assume that studies were estimating the same underlying treatment effects. Pooled estimates of outcomes variables showing I2 >50% were presented using random effects model, restricted maximum likelihood method.21 

We planned to perform a subgroup analyses for infants <32 weeks’ gestational age (very preterm) or <1500 g birth weight (very LBW) for the primary outcomes.

The certainty of the evidence for each outcome was assessed independently by 2 review authors using the Grading of Recommendations Assessment, Development, and Evaluation approach using Grading of Recommendations Assessment, Development, and Evaluation Pro guideline development tool,22  a Web-based tool to create a “summary of findings” table to report the certainty of the evidence (Appendix 8 and 11).

We found 2200 records. After removing duplicates, title, abstract, and full text screening, we included 4 reports (3 studies) that compared outcomes in calcium- or phosphorus-supplemented infants to infants who did not receive calcium or phosphorous (Appendix 3).2326  There were no studies that compared dose or timing of calcium or phosphorous supplementation in preterm or LBW infants. A total of 34 studies were excluded in this review (Appendix 6).

The included studies (2 RCTs and 1 quasi-randomized trial) reported on 162 preterm or LBW infants from 2 countries (Iran, United Kingdom) (Appendix 5). Two studies assessed the effect of phosphorus only (dose of 15 mg/kg per day in 1 study and 50–75 mg per day in 1 study) and 1 study assessed the effect of calcium and phosphorous combined (calcium 45 mg/kg per day, phosphorus 25 mg/kg per day). Supplementation commenced between birth and 10 days postnatal age in all 3 studies. The duration of supplementation was between 10 and 42 days in 1 study and it could not be assessed in the other 2 included studies.

The ROB assessment is summarized in Appendix 4. One study had low ROB,23  1 high ROB,25  and 1 moderate ROB.24 

Results are summarized in Table 1 and Appendix 7. There were no mortality or neurodevelopment outcome data available for analysis.

TABLE 1

Summary of Findings for Critical Outcomes

Calcium and/or Phosphorus Supplementation Compared With No Supplement for Preterm and/or LBW Infants
Anticipated Absolute Effects
OutcomesNo. of Participants (Studies) Follow-up(GRADE) Certainty of the EvidenceRelative Effect (95% CI)Risk With No SupplementRisk Difference With Calcium and/or Phosphorus Supplementation
Weight (g) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean weight (g) was 2483 g MD 138.5 g higher
(82.16 lower–359.16 higher) 
Length (cm) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean length (cm) was 47.04 cm MD 0.77 cm higher
(0.92 lower–2.46 higher) 
Head circumference (cm) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean head circumference (cm) was 34.31 cm MD 0.33 cm higher (0.3 lower–0.96 higher) 
Serum alkaline phosphatase (IU/L) follow-up: latest mean (SD) 55 (69.3) wk; median (IQR) 55 (6–104) wk 122 (2 RCTs) ⨁◯◯◯ Very lowb — The mean serum alkaline phosphatase (IU/L) was 656.13 IU/L MD 126.11 IU/L lower
(298.5 lower–46.27 higher) 
Serum calcium (mg/dL) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean serum calcium (mg/dL) was 8.39 mg/dL MD 0.54 mg/dL higher
(0.19 lower–1.27 higher) 
Serum phosphorus (IU) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean serum phosphorus (IU) was 4.36 IU MD 0.07 IU higher (0.22 lower–0.36 higher) 
Osteopenia/rickets follow-up: latest mean (SD) 38.3 (56.9) wk; median (IQR) 6 (5–104) wk 159 (3 RCTs) ⨁⨁◯◯ Lowc RR 0.68 (0.46–0.99) 540 per 1000 173 fewer per 1000 (292 fewer–5 fewer) 
Calcium and/or Phosphorus Supplementation Compared With No Supplement for Preterm and/or LBW Infants
Anticipated Absolute Effects
OutcomesNo. of Participants (Studies) Follow-up(GRADE) Certainty of the EvidenceRelative Effect (95% CI)Risk With No SupplementRisk Difference With Calcium and/or Phosphorus Supplementation
Weight (g) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean weight (g) was 2483 g MD 138.5 g higher
(82.16 lower–359.16 higher) 
Length (cm) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean length (cm) was 47.04 cm MD 0.77 cm higher
(0.92 lower–2.46 higher) 
Head circumference (cm) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean head circumference (cm) was 34.31 cm MD 0.33 cm higher (0.3 lower–0.96 higher) 
Serum alkaline phosphatase (IU/L) follow-up: latest mean (SD) 55 (69.3) wk; median (IQR) 55 (6–104) wk 122 (2 RCTs) ⨁◯◯◯ Very lowb — The mean serum alkaline phosphatase (IU/L) was 656.13 IU/L MD 126.11 IU/L lower
(298.5 lower–46.27 higher) 
Serum calcium (mg/dL) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean serum calcium (mg/dL) was 8.39 mg/dL MD 0.54 mg/dL higher
(0.19 lower–1.27 higher) 
Serum phosphorus (IU) follow-up: 6 wk 40 (1 RCT) ⨁◯◯◯ Very lowa — The mean serum phosphorus (IU) was 4.36 IU MD 0.07 IU higher (0.22 lower–0.36 higher) 
Osteopenia/rickets follow-up: latest mean (SD) 38.3 (56.9) wk; median (IQR) 6 (5–104) wk 159 (3 RCTs) ⨁⨁◯◯ Lowc RR 0.68 (0.46–0.99) 540 per 1000 173 fewer per 1000 (292 fewer–5 fewer) 

The risk in the intervention group (and its 95% CI) is on the basis of the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). Grading of Recommendations Assessment, Development, and Evaluation Working Group grades of evidence: high certainty, we are very confident that the true effect lies close to that of the estimate of the effect; moderate certainty, we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different; low certainty, our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect; very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. Patient or population: preterm and/or LBW infants. Setting: any high-, middle-, or low-income country; at home or in the health facility. Intervention: calcium and/or phosphorus supplementation. Comparison: no supplement. GRADE, Grading of Recommendations Assessment, Development, and Evaluation; IQR, interquartile range; RCT, randomized controlled trial. —, not applicable.

a

Downgraded 3 levels for: very serious ROB; serious inconsistency (small number of studies); serious imprecision (wide CI).

b

Downgraded 3 levels for: very serious ROB; serious inconsistency (high heterogeneity [I2 = 73.42%]); serious imprecision (wide CI).

c

Downgraded 2 levels for: serious ROB; serious imprecision (suboptimal sample size).

At latest follow-up (mean [SD] 38.3 [56.9] weeks), when comparing calcium- or phosphorus-supplemented infants to unsupplemented infants, the RR for osteopenia was 0.68 (95% CI 0.46–0.99, 3 studies, 159 participants, low certainty evidence).2325 

At latest follow-up (6 weeks), the MD between the calcium- or phosphorus-supplemented infants compared with the unsupplemented infants in weight was 138.50 g (95% CI −82.16 to 359.16, 1 study, 40 participants, very low certainty evidence)25 ; in length was 0.77 cm (95% CI −0.93 to 2.47, 1 study, 40 participants, very low certainty evidence)25 ; and head circumference was 0.33 cm (95% CI −0.30 to 0.96, 1 study, 40 participants, very low certainty evidence).25 

At latest follow-up, the MD between the calcium- or phosphorus-supplemented infants compared with the unsupplemented infants in alkaline phosphatase (55 weeks) was 126.11 IU/L (95% CI −298.5 to 46.27, I2 = 73.4%, 2 studies, 122 participants, very low certainty evidence)24,25 ; serum calcium (6 weeks) was 0.54 mg/dL (95% CI −0.19 to 1.27, 1 study, 40 participants, very low certainty evidence)25 ; and in serum phosphorus (6 weeks) was 0.07 mg/dL (95% CI −0.22 to 0.36, 1 study, 40 participants, very low certainty evidence).25 

For infants <32 weeks’ gestational age or birth weight <1500 g, results are summarized in Appendices 9-11. There were no mortality or neurodevelopment outcome data available for analysis. At latest follow-up (mean [SD] 54.5 [70.0] weeks), when comparing calcium- or phosphorus-supplemented infants to unsupplemented infants, the RR for osteopenia was 0.29 (95% CI 0.02–3.64, I2 = 70.8%, 2 studies, 119 participants, very low certainty evidence).23,24  At latest follow-up, the MD between the calcium- or phosphorus-supplemented infants compared with the unsupplemented infants in serum alkaline phosphatase was −237.8 IU/L (95% CI −415.18 to −60.42, 1 study, 82 participants, very low certainty evidence).24 

Three studies of 162 infants that compared calcium or phosphorus supplementation versus no supplementation in preterm or LBW infants were included in this review. We found low certainty evidence of reduction in osteopenia but no change in markers of growth (weight, length, and head circumference at 6 weeks follow-up). There was very low certainty evidence showing an improvement in alkaline phosphatase among infants <1.5 kg or <32 weeks’ gestation at birth, but no other change in markers of bone metabolism (serum calcium or phosphorous levels). There were no studies that reported mortality, or other morbidities including bone fractures and infection, and no studies that reported developmental outcomes. We found no studies that compared dose or timing of calcium or phosphorus supplementation.

The most recent 2017 Cochrane systematic review9  included 1 trial of 40 infants and reported similar findings that there was no evidence of a difference between calcium and phosphorus supplementation versus no supplementation for neonatal growth outcomes and a decrease in serum alkaline phosphatase concentration (MD −56.85 IU/L, 95% CI −101.27 to −12.43) at 6 weeks’ postnatal age. There has been no other recent systematic reviews on calcium or phosphorous supplementation for preterm or LBW infants in either hospital or community settings.

The lack of data on calcium and phosphorus supplementation is likely because of many infants receiving human milk multicomponent fortifier that contains calcium and phosphorus, along with other micronutrients such as vitamins, minerals, energy, and protein. There have been many trials of human milk multicomponent fortification and a recent Cochrane systematic review published in 2018.27  That systematic review reported an increased rate of weight gain (MD 1.76 g/kg per day, 95% CI 1.30–2.22), body length (MD 0.11 cm per week, 95% CI 0.08–0.15) and head circumference (MD 0.06 cm per week, 95% CI 0.03–0.08) among preterm infants.28  Also, a reduction in markers of bone metabolism, serum alkaline phosphatase levels (weighted mean difference −142 IU/L (95% CI −204 to −80) and higher bone mineral content (weighted mean difference 12.0 mg/cm (95% CI 6.3–17.7) was reported with human milk fortification of multinutrients including calcium and phosphorus.28  However, human milk fortification is more expensive than calcium or phosphorus supplements and also requires mixing of fortifier with breast milk or provision of donor milk with possible concerns of increased risks of contamination.

Limitations of our review included the small number of studies and participants, the high ROB, and the heterogeneity in outcomes. However, strengths were our comprehensive search strategy and systematic review methods including assessment of certainty of body of evidence using standard methods. The doses of calcium and phosphorus used in the studies were similar to those recommended by WHO10  and other organizations, meaning our results are generalizable to low- and middle-income country settings that use WHO guidelines.

Overall, evidence is insufficient to reveal whether supplementation with calcium and phosphorus improved growth and bone health of preterm or LBW infants. Given the importance of calcium and phosphorous supplementation in preterm and LBW infants, more high-quality trials of these supplements are needed.

The Society for Applied Studies thanks the core support provided by the Department of Maternal, Newborn, Child and Adolescent Health, WHO, Geneva (WHO Collaborating Centre IND–158).

Drs Kumar and Choudhary conceptualized and designed the study, designed the data collection instruments, collected data, conducted the initial analyses, prepared the initial draft, and revised the manuscript; Dr Chowdhury conceptualized and designed the study, and critically reviewed the manuscript; Drs Sinha, Upadhyay, Chandola, Mazumdar, Taneja, and Bhandari coordinated and supervised data collection, and critically reviewed the manuscript; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

This study is registered at PROSPERO, #CRD42021238802, https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021238802.

FUNDING: Supported by the Department of Maternal, Newborn, Child and Adolescent Health and Ageing, World Health Organization (WHO), Geneva, Switzerland. The sponsor (WHO) commissioned the review for a guideline development group meeting for development of WHO recommendations on care of the preterm or low birth weight infant. The sponsor assisted in formulating the research question and provided inputs on the synthesis of the results and manuscript.

CONFLICT OF INTEREST DISCLAIMER: The authors have indicated they have no conflicts relevant to this article to disclose.

     
  • CI

    confidence interval

  •  
  • LBW

    low birth weight

  •  
  • MD

    mean difference

  •  
  • ROB

    risk of bias

  •  
  • RR

    relative risk

  •  
  • WHO

    World Health Organization

1
Ballard
O
,
Morrow
AL
.
Human milk composition: nutrients and bioactive factors
.
Pediatr Clin North Am
.
2013
;
60
(
1
):
49
74
2
Butte
NF
,
Lopez-Alarcon
MG
,
Garza
C
.
WHO, Department of Nutrition for Health and Development, Department of Child and Adolescent Health and Development
.
Nutrient Adequacy of Exclusive Breastfeeding for the Term Infant During the First Six Months of Life
.
Geneva
:
World Health Organization
;
2002
3
Underwood
MA
.
Human milk for the premature infant
.
Pediatr Clin North Am
.
2013
;
60
(
1
):
189
207
4
Bhatia
J
.
Human milk and the premature infant
.
Ann Nutr Metab
.
2013
;
62
(
Suppl 3
):
8
14
5
Kumar
A
,
Kaur
S
.
Calcium: a nutrient in pregnancy
.
J Obstet Gynaecol India
.
2017
;
67
(
5
):
313
318
6
Atkinson
SA
,
Radde
IC
,
Anderson
GH
.
Macromineral balances in premature infants fed their own mothers’ milk or formula
.
J Pediatr
.
1983
;
102
(
1
):
99
106
7
Rowe
J
,
Rowe
D
,
Horak
E
, et al
.
Hypophosphatemia and hypercalciuria in small premature infants fed human milk: evidence for inadequate dietary phosphorus
.
J Pediatr
.
1984
;
104
(
1
):
112
117
8
Rowe
JC
,
Wood
DH
,
Rowe
DW
,
Raisz
LG
.
Nutritional hypophosphatemic rickets in a premature infant-fed breast milk
.
N Engl J Med
.
1979
;
300
(
6
):
293
296
9
Harding
JE
,
Wilson
J
,
Brown
J
.
Calcium and phosphorus supplementation of human milk for preterm infants
.
Cochrane Database Syst Rev
.
2017
;
2
(
2
):
CD003310
10
WHO
.
Guidelines on Optimal Feeding of Low Birth Weight Infants in Low- and Middle-income Countries
.
Geneva
:
World Health Organization
;
2012
11
Choudhary
T
,
Sinha
B
,
Chowdhury
R
, et al
.
Enteral calcium and phosphorous supplementation in preterm or low birth weight infants
.
12
Cochrane Controlled Register of Trials (CENTRAL)
.
Available at: https://www.cochranelibrary.com/central/about- central. Accessed November 16, 2021
13
PubMed
.
Available at: https://pubmed.ncbi.nlm.nih.gov/. Accessed November 16, 2021
14
Embase
.
Available at: https://www.embase.com/landing?status=grey. Accessed November 16, 2021
15
Covidence
.
Better systematic review management
.
Available at: www.covidence.org. Accessed November 16, 2021
16
Higgins
JPT
,
Thomas
J
,
Chandler
J
, et al, editors.
Cochrane Handbook for Systematic Reviews of Interventions Version 6.2
.
Available at: www.training.cochrane.org/handbook. Accessed November 16, 2021
17
Cochrane Effective Practice and Organisation of Care (EPOC)
.
EPOC Resources for review authors
.
Available at: epoc.cochrane.org/epoc-resources- review-authors. Accessed November 16, 2021
18
Sterne
JAC
,
Savović
J
,
Page
MJ
, et al
.
RoB 2: a revised tool for assessing risk of bias in randomised trials
.
BMJ
.
2019
;
366
:
l4898
19
Mavridis
D
,
Salanti
G
.
How to assess publication bias: funnel plot, trim-and-fill method and selection models
.
Evid Based Ment Health
.
2014
;
17
(
1
):
30
20
StataCorp
.
Stata Statistical Software: Release 16
.
College Station, TX
:
StataCorp LLC
;
2019
21
Higgins
JPT
,
Thompson
SG
,
Deeks
JJ
,
Altman
DG
.
Measuring inconsistency in meta-analyses
.
BMJ
.
2003
;
327
(
7414
):
557
560
22
McMaster University
.
GRADEpro GDT: GRADEpro guideline development tool
.
Available at: https://gradepro.org/cite/gradepro.org. Accessed November 16, 2021
23
Holland
PC
,
Wilkinson
AR
,
Diez
J
,
Lindsell
DR
.
Prenatal deficiency of phosphate, phosphate supplementation, and rickets in very low birth weight infants
.
Lancet
.
1990
;
335
(
8691
):
697
701
24
McIntosh
N
,
De Curtis
M
,
Williams
J
.
Failure of mineral supplementation to reduce incidence of rickets in very-low-birthweight infants
.
Lancet
.
1986
;
2
(
8513
):
981
982
25
Torabi
Z
,
Moemeni
N
,
Ahmadiafshar
A
,
Mazloomzadeh
S
.
The effect of calcium and phosphorus supplementation on metabolic bone disorders in premature infants
.
J Pak Med Assoc
.
2014
;
64
(
6
):
635
639
26
Torabi
Z
,
Moemeni
N
,
Mazloozadeh
S
.
Evaluation and comparison of calcium and phosphorus in the improvement of metabolic bone disorder in premature infants
.
Arch Dis Child
.
2012
;
97
(
suppl 2
):
A386
A386
27
Quigley
M
,
Embleton
ND
,
McGuire
W
.
Cochrane Neonatal Group
, editor.
Cochrane Database of Systematic Reviews. Formula versus donor breast milk for feeding preterm or low birth weight infants
.
Available at: https://doi.wiley.com/10. 1002/14651858.CD002971.pub4. Accessed November 16, 2021
28
Brown
JVE
,
Lin
L
,
Embleton
ND
,
Harding
JE
,
McGuire
W
.
Cochrane Neonatal Group
, editor.
Cochrane Database of Systematic Reviews. Multinutrient fortification of human milk for preterm infants
.
Available at: http://doi.wiley.com/10.1002/14651858.CD000343.pub4. Accessed November 16, 2021
This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Supplementary data