Indian Pediatrics 2004; 41:63-67 

Effect of Fortification with Human Milk Fortifier (HMF) and other Fortifying Agents on the Osmolality of preterm Breast Milk

Key words: Coconut oil, Fortification, Human milk fortifier (HMF), LBW formula, Osmolality.

Human milk feeding has been shown to be of enormous advantages in preterm infant(1-3). Few studies have observed that human milk-fed preterm infants have slower growth rate and inadequate specific nutrient intake to meet their proportionately greater needs(1,4). Fortification of human milk has been therefore recommended. Human milk fortifier (HMF) has been available in India since late nineties but its safety and efficacy has still not been established. Other means of fortification include LBW formula and coconut oil. Fortification can result in increase in milk osmolality(5-6), which may be associated with adverse effects such as feed intolerance and necrotizing enterocolitis(7-8).The present study evaluated the effect of fortification with HMF, LBW formula and coconut oil on the osmolality of preterm breast milk.

Subjects and Methods

It was a prospective, blinded study conducted at a tertiary care institute enrolling women delivered before or at 34 weeks. Written informed consent was taken. Milk was expressed manually or using electric breast pump.

Fortification of breast milk was done with Human Milk Fortifier (Lactodex-HMF; Raptakos, Brett and Co. Ltd.; 4 g/100 mL of milk), LBW formula (Raptakos, Brett and Co. Ltd; 4 g/100 mL) and edible coconut oil (2 mL/100 mL). A comparison of the various compositions is provided in Table I.

Osmolality was measured by AdvancedTM Micro-Osmometer, model 3300 (Advanced Instruments Inc, MA USA) by a technician blinded to fortification. The equipment works on the principle of freezing point measure-ment with precision of 2 mOsm/Kg. The osmolality of fortifying agents dissolved in water at the same concentration as used for fortification (Ofw) was measured. By adding measured osmolality of milk and Ofw, expected rise in osmolality of milk on fortification was calculated. Milk osmolality was measured after fortification at 20 minutes and at 6 hrs (after storing at 4ºC). To detect a difference of 20 mOsm/kg in milk osmolality (alpha-0.05 and beta-0.2), 40 milk samples were needed. Paired two tailed Student t-test was applied.

Results

Forty eight milk samples were tested from 25 mothers (multiple samples from 14 mothers at different postnatal age). The demographic details are provided in Table II.

The osmolality of breast milk with and without fortification is provided in Table I. There was no change in osmolality of breast milk after storage for 6 h. The fortification of breast milk with HMF and LBW formula resulted in significant rise in osmolality (P <0.0001). However, no further change in osmolality was observed on storage for 6 h. Addition of coconut oil did not make any significant difference in osmolality at 20 min and after 6 h of storage.

Table I

Composition and Osmolality of Breast Milk (per 100 mL) with and without 
Fortification 

Ingredients	Breast milk	Breast milk + HMF* (4 g/100 mL)	Breast milk + LBW formula† (4 g/100 mL)	Breast milk + coconut oil‡ (2 mL/100 mL)
Calories	65	78	81	83
Proteins (g)	1.6	2	2.1	1.6
Carbohydrates (g)	7	9.4	9.2	7
Fat (g)	4	4.2	5	6
Calcium (mg)	40	140	72	40
Phosphorus (mg)	20	70	36	20
Vitamin A (IU)	250	1700	310	250
Vitamin D (IU)	2.5	500	22.5	2.5
Sodium (mEq)	0.8	1.6	1.3	0.8
Iron (mcg)	300	300	500	300
Folate (mg)	5	6	17	5
Osmolality at 20 minutes (mOsm/kg)	302.3 ± 1.82	392.9 ± 3.01	390.5 ± 2.4	304 ± 1.6
Osmolality after 6 hr mOsm/kg)	301 ± 1.75	393.3 ± 3.0	390.7 ± 2.3	303.6 ± 1.6

*HMF (Human Milk Fortifier): All components except sodium meet the nutritional 
requirement.
†LBW formula: Calcium, phosphorus, sodium inadequate; calories adequate.
‡Coconut oil: Only the calorie content is increased.

TABLE II

Demographic Characteristics of Study Population 

Maternal details (n = 25)
Age (range)	26 years (25-30)
Height (range)	155 cm (140-160)
Parity (range)	1 (1-3)
Delivery by LSCS (%)	17 (68%)
Pregnancy induced hypertension (%)	9 (36.1)
Anemia (%)	8 (32%)
Neonatal details (n = 25)
Gestational age (range)	31(29-32 wks)
Birth weight (range)	1198 g (716-1478 g)
Small for gestational age (%)	11 (42.3%)
Postnatal age at testing milk (range)	15 days (3-60 days)

The observed osmolality change with addition of HMF and LBW formula was significantly higher than the expected osmolality (Table III). However, with coconut oil, the osmolality of breast milk remained unaltered. No further change was seen after storage for 6 hours with any of the fortifying agents.

TABLE III

Comparison of Observed Vs Expected Change in 
Osmolality* at 20 Minutes and 6 Hours. 

Fortification	Expected change* in osmolality at 20 min (Agent + water)	Observed change in osmolality at 20 min (Agent + milk)	Expected change* in osmolality at 6 hours (Agent + water)	Observed change in osmolality at 6 hours (Agent + milk)
HMF	54.9 ± 0.9	92.8 ± 2.1†	55.1 ± 0.9	92.8 ± 2.1†
LBW formula	56.6 ± 0.5	88.3 ± 2.1†	56.2 ± 0.5	88.4 ± 2†
Coconut oil	3.6 ± 0.4	1.8 ± 0.9	3.0 ± 0.4	1.4 ± 0.8

All values (mOsm/kg) expressed as mean ± standard error (range)
*Expected change in osmolality was estimated as the osmolality of the fortifying 
agent dissolved in water (in the same concentration used to forify breast milk)
†Comparison of expected vs observed change in osmolality, p value <0.001

Discussions

Our study demonstrated that osmolality of breast milk increases significantly on fortification with HMF and LBW formula. However, it remains unaltered on addition of coconut oil. The increase in osmolality was significantly higher than expected value. There was no effect of storage at 4ºC for 6 hours on the osmolality of milk.

DeCurtis, et al.(5) measured the effect of fortification with different HMF preparation on the osmolality of milk. Significant increase in osmolality was demonstrated on addition of HMF. The increase in osmolality depended upon composition of HMF. With a protein based HMF, increase in osmolality was equal to the expected value at 10 minutes with no late rise while significant increase with late rise in osmolality was noted with carbo-hydrate based HMF. Linear regression analysis showed that the total dextrin content determined increase in osmolality. Jocson, et al.(6) also reported early as well as late rise osmolality of breast milk with HMF forti-fication. Our results were consistent with the above studies.

The HMF and LBW formula used in present study is predominantly maltodextrin based. Higher than expected increase in osmolality could be due to breakdown of maltodextrin by amylase present in breast milk(5). The polysaccharides are broken down into smaller molecules by the amylase enzyme resulting in a higher number of osmotically active molecules. Bacterial degradation of constituents as a possible mechanism for unexpected increase in osmolality(6) seemed improbable since there was no late rise in osmolality.

Osmolality is a critical determinant of feed tolerance(5-6). Milk fortification results in significant increase in osmolality(5,6). Cochrane meta-analysis has shown an increased tendency for feed intolerance with fortified milk(7). Feed intolerance may result in the reduction in nutrient intake which can explain lower weight gain compared to formula in VLBW infants(7). An association between hyper-osmolar feeds (³400 mOsm/kg) and necrotizing enterocolitis has also been reported(8).

There is need to develop safer preparations of HMF, which can provide additional nutrients in VLBW infants. Since fat is not osmotically active, it may be preferable to use a predominantly fat based HMF. However, fat delays the gastric emptying with an attendant risk of feed intolerance and reduction in overall calorie intake resulting in no effect on growth velocity(3).

We conclude that available preparation of HMF as well as practice of supplementing human milk with LBW formula may not be safe because of significant increase in osmo-lality. There is a need to develop a safer pre-paration of HMF for VLBW population in India.

Contributors: All were involved in design of study. RAG, AS collected and analyzed the data. RAG drafted the manuscript which was edited by RAGG. AKD and VKP did critical review. RAGG will act as guarantor.

Funding: None.

Competing interests: None stated.

 References