Early Human Development, 1980,4/4, 365-372 o Elsevier/North-Holland Biomedical Press

365

The nipple-shield sampling system: a device for measuring the dietary intake of breast-fed infants

ALAN LUCAS*, PENNY J. LUCAS* and J. DAVID BAUM

University Department of Paediatrics, John Radcliffe Hospital, Oxford, United Kingdom

Accepted for publication 24 July 1980

SUMMARY

We have devised a method for the determination of the composition of the milk infants obtain from the breast during suckling itself, suckled breast milk (SBM). The method involves the use of a nipple-shield sampling system, together with data on the pattern of milk flow from mother to infant derived from a cross-sectional analysis of test weighings during feeding.

In this study, marked changes were demonstrated in milk fat concentration and energy value during a breast feed in 10 term infants on the sixth day postpartum. From this information the total intake of fat and energy during the feed was calculated. These preliminary findings suggest that published information on the dietary intake of breast-fed infants may need some revision.

breast-fed; human milk; composition; nipple-shield

INTRODUCTION

There is a substantial body of published data on the composition of human milk. However, in nearly all cases the milk that has been analysed has been removed from the breast unphysiologically by manual or mechanical expres- sion. We have speculated previously [ 41 that expressed breast milk might not accurately reflect the dietary intake of breast-fed infants, yet there is no information on the milk that an infant obtains physiologically during suckling, suckled breast milk (SBM). We now report on a method that has

*Now at Addenbrooke’s Hospital, Cambridge, U.K. Correspondence to Dr. J.D. Baum.

366

been devised for analysing the composition of SBM. Such an analysis requires information both on milk flow and on milk composition, since these two variables change continuously during each feed.

A modified latex nipple shield has been devised to permit measurement of milk composition on small sequential milk samples obtained during a breast feed. Milk flow during feeding can be assessed for a population of mother- infant pairs using a cross-sectional analysis of test weighings [6] which avoids repeated interruptions of individual feeds. In this report we show how, using this method, the fat content and energy value of SBM can be calculated.

SUBJECTS AND METHODS

The nipple-shield sampling system

A latex nipple shield* has’ been devised as illustrated in Figure 1. It comprises 3 portions: (i) a thickened rim (1.5 mm thick X 1 cm wide) which is applied to the breast beyond the areola; (ii) a thickened central conical portion overlying the nipple, 1.5 mm thick and produced in two heights, 1.4 or 1.8 cm, with a base width-to-height ratio of 1; (iii) a middle zone, which is sufficiently thin to adhere closely to the breast (0.1 mm thick X 2.0 cm wide) and permit the areola to be drawn into mouth as occurs during normal feeding. A sampling line is introduced into the nipple shield cavity, as illustrated, to permit small sequential samples to be removed during feeding (cumulatively amounting to less than 5% of the total feed volume).

Ten healthy mother-infant pairs were studied using this device during a feed (2nd or 3rd feed of the day) on the sixth postnatal day. Milk samples were taken at 1-min intervals during a feed from the first breast, and in 6 cases the study was continued during a feed from the second breast. The infants were full-term with a mean birth weight (? SEM) of 3370 (+ 30) g. These samples were analysed for fat concentration and energy value by means of the ‘creamatocrit’ technique [ 51.

Pattern of milk flow curves

Forty-nine breast-fed healthy term infants were studied during a single breast-feed (2nd or 3rd feed of the day) on the sixth postnatal day. During feeding the nipple shield was in place, but no samples were taken during this part of the study. Cross-sectional data was built up in the following manner. Infants were weighed before the feed and at either 2 min (N = 6), 4 min (N = S), or 7 min (N = 6) after the beginning of the feed. The difference between the first and second weighing represented the ingested milk volume

*Available from: Lewis,Woolf Griptight Ltd., 144 Oakfield Road, Birmingham, U.K.

3‘67

Milk

Flow

c Milk samples

Fig. 1. Nipple shield-sampling device. On left: Photograph of actual shield with sampling line emerging from it. On right: Diagrammatic section of shield and its sampling line.

(assuming milk density of 1 g/ml). Three other groups of infants were weighed at the same times during feeding on the second breast (N = 20). Another group was weighed 3 times: before the start of the feed on the first breast, during the change over to the second breast, and after the end of the feed on the second breast (N G 10). The last group provided the mean total first-breast and second-breast milk intake, and from this the mean proportion of the feed taken after 2,4, or 7 min was calculated. (One infant was excluded from the series, since the mother was unable to maintain the shield in position during feeding.)

Weighings were done on a purpose-modified electronic balance (Sartorius, 3806 M.P.), which calculated the mean of 10 automatic measurements taken in rapid succession. Such weighings substantially reduced artefacts due to infant movement and were accurate to 1 g.

368

RESULTS

Pattern of milk flow

The pattern of milk flow curve is compared in Figure 2, with the pattern described previously [6], in a similar population of mother-infant pairs at the same postpartum age who were not using the nipple, shield during feeding. No significant differences were found between the two groups at any time period during a feed, indicating that the shield did not significantly impede or alter milk flow. The mean total milk intake (* SEM) for the first breast was 36 (* 4) ml and the second breast 30 (? 5) ml with the shield in place, compared with, respectively, 37 (+ 2) ml and 29 (+ 3) ml reported previously [4] for a feed without the use of the shield.

a 12

40

b 40 r

0 2 4 I 10

min

Fig. 2. Pattern of milk intake with and without the nipple shield in place (ml * SEM), during a feed from (a) the first breast or (b) the second breast.

TAB

LE I

Fat

and

calo

ric

conc

entr

atio

ns

and

milk

vol

ume

for

each

min

ute

of t

he f

eed,

wit

h ca

lcul

ated

fa

t co

nten

t an

d en

ergy

val

ue f

or e

ach

min

ute

and

henc

e th

e w

hole

fe

ed

Min

utes

of

feed

Firs

t br

east

(N

= 1

0)

Seco

nd

brea

st (

N =

6)

1 2

3 4

5 6

I 8

9 10

1

2 3

4 5

6 7

8 9

10

Fat

conc

entr

atio

n g/

100

ml

(SE

M)

(%)

(Z)

(G)

$35)

(Z

) (Z

) kc

ai/lO

O m

l (S

EM

) 54

52

53

57

62

65

(3

) (2

) (2

) (3

) (4

) (4

) C

alcu

late

d m

l of

fee

d ta

ken

for

each

min

* 8

8 8

8 1

1 Fa

t co

nten

t of

eac

h m

m o

f fe

ed (

g)

0.17

0.

16

0.17

0.

2 0.

03

0.03

kc

aI c

onte

nt

of e

ach

min

of

feed

4.

3 4.

2 4.

2 4.

6 0.

6 0.

7 To

tal

fat

and

kcaI

con

cent

rati

on

Fat:

2.5

g/l0

0 m

l

70

70

75

73

63

54

56

59

60

62

65

69

69

- (4

) (5

) (6

) (4

) (8

) (6

) (7

) (6

) (7

) (7

) (7

) (8

) (8

)

0.5

0.5

0.5

0.5

6 6

5 3

3 2

2 2

1 0

0.02

0.

02

0.02

0.

02

0.19

0.

13

0.12

0.

08

0.08

0.

06

0.07

0.

07

0.04

-

0.4

0.4

0.4

0.4

3.8

3.2

2.8

1.8

1.8

1.2

1.3

1.4

0.7

-

Ene

rgy

valu

e: 5

8 kc

ai/lO

O

ml

*The

se f

igur

es h

ave

been

der

ived

fro

m t

he f

low

cur

ves

in F

ig.

2 (w

ith

the

shie

ld i

n us

e).

370

Fat concentration and energy value during a feed

Table I shows the fat content (also on Fig. 3) and energy value of samples taken at 1-min intervals during a feed from first and second breast. The 2- fold rise in mean fat content and energy value during the first to the tenth minute of feeding from the first breast was significant by the Wilcoxon signed ranks matched pairs test (P < 0.01). On the second breast there was an initial fall in fat concentration and energy values which did not reach significance, but the subsequent rise in these values by the end of the feed was significant (P < 0.05).

The calculation of SBM con tent

In Table I the calculated volume of milk taken during each minute of the feed is shown. These values are based on the total milk flow and the pattern of milk flow (Fig. 2). From this, the fat concentration and energy values for each minute of the feed have been calculated (also shown on the Table). The

T

P T T

::;;

First Breast Second breast

II I I I I I I I I L I III1 I 11 I

1 2 3 4 5 6 7 8 9 10 0123456789

Time, min

Fig. 3. Change in fat concentration (t SEM) during a feed from the first breast (left, N = 10) or second breast (right, N = 6).

total concentration of fat and energy value in the feed from both breast (66 ml) was respectively 2.6 g/100 ml and 58 kcal/lOO ml.

DISCUSSION

Previous studies on human lactation have involved obtaining milk unphysiologically by expression of the breast. The present study is also open to the criticism that the presence of the latex nipple shield might involve some disturbance to normal feeding. The latex nipple shield differs from the conventional rubber nipple shields used in clinical practice in two main respects. Firstly, in a population of mother-infant pairs, the shield did not significantly disturb the pattern or total amount of milk flow during feeding (Fig. 2). Secondly, Woolridge et al. have shown that, unlike the rubber nipple shield, the presence of the latex shield does not measurably affect the normal pattern of infant sucking at the breast [8] . Thus it is likely that the sequential samples of milk obtained were representative of the milk that the infant consumed at each stage of the feed.

Changes in milk fat concentration have been described previously by Hytten [l] , using a mechanical breast pump to obtain the milk samples. Our studies demonstrate that the mean fat concentration doubled during the course of a feed on the first breast, though the range in values was large. Analysis of the small number of observations made during a feed on the second breast showed that the fat concentration tended to fall initially, but then rose significantly towards the end of the feed.

The latex shield can be used to investigate several aspects of lactation, for example, the changes in concentration of other milk components during a feed and the pattern of maternal drug excretion into milk. However, a know- ledge of compositional changes in milk during feeding cannot be used alone to determine the dietary intake of breast-fed infants. These changes must be related to milk flow. Since 80-90% of the feed from each breast (Fig. 2) is consumed within 4 min, the high-fat, energy-rich hindmilk is consumed only in very small amounts. We have used population data to determine the pattern of milk flow. This data was used to calculate the mean volume of milk taken during each minute of the feed so that the fat content and energy value for each time period of the feed could be derived. This method for estimating milk flow and composition cannot be applied to individual subjects but is suitable for the investigation of the average dietary intake of relatively homogenous populations of mother-infant pairs.

At present we have calculated only fat and energy intakes on the sixth postpartum day in Oxford infants. At this stage in lactation overall mean fat concentration and energy value of a feed taken in the middle of the day (when the fat concentration is highest [2] were respectively 2.5 g/100 ml and 58 kcal/lOO ml. Previous reports by Macy [ 71 and Hytten [3] have shown that the mean fat concentration at this stage in lactation is over 3 g/l00 ml. The relatively low fat concentration in SBM raises the possibility

372

that published figures for the fat content of EBM may not be a correct representation of breast-fed infants intake. Further studies throughout the course of lactation may provide information of relevance to the design of future artificial infant formulae.

ACKNOWLEDGEMENTS

A.L. and P.J.L. are in receipt of an ICIFI research grant.

REFERENCES

1 Hytten, F.E. (1954): Clinical and chemical studies in human lactation. II. Variation in major constituents during a feeding. Br. Med. J., i, 176-179.

2 Hytten, F.E. (1964): Clinical and chemical studies in human lactation. III. Diurnal variation in major constituents in milk. Br. Med. J., i, 179-182.

3 Hytten, F.E. (1954): Clinical and chemical studies in human lactation. IV. Trends in milk composition during the course of lactation. Br. Med. J., i, 249-265.

4 Lucas, A., Gibbs, J.H. and Baum, J.D. (1977): What is breast milk? Lancet, ii, 1011. 5 Lucas, A., Gibbs, J.H., Lyster, R.L.J. and Baum, J.D. (1978): Creamatocrit: a simple

technique for estimating fat concentration and energy value in human milk. Br. Med. J., i, 1018-1019.

6. Lucas, A., Lucas, P.J. and Baum, J.D. (1979): Pattern of milk flow in breast-fed infants. Lancet, ii, 57-58.

7 Macy, I.G. and Kelly, J.H. (1961): Human milk and cow’s milk in infant nutrition. In: Milk: The Mammary Gland and its Secretion, Vol. 2, p. 265. Editors: SK. Kow and A.T. Cowie. Academic Press, New York-London.

8 Woolridge, M.W., Baum, J.D. and Drewett, R.F., (1980): Effects of a traditional and of a new nipple shield on sucking patterns and milk flow. Early Hum. Dev. 4, 357- 364.