Peter E. Hartmann

Volume and Frequency of Breastfeedings and Fat Content of Breast Milk Throughout the Day

OBJECTIVE. We aimed to provide information that can be used as a guide to clinicians when advising breastfeeding mothers on normal lactation with regard to the frequency and volume of breastfeedings and the fat content of breast milk. METHODS. Mothers (71) of infants who were 1 to 6 months of age and exclusively breastfeeding on demand test-weighed their infants before and after every breastfeeding from each breast for 24 to 26 hours and collected small milk samples from each breast each time the infant was weighed. RESULTS. Infants breastfed 11 ± 3 times in 24 hours (range: 6–18), and a breastfeeding was 76.0 ± 12.6 g (range: 0–240 g), which was 67.3 ± 7.8% (range: 0–100%) of the volume of milk that was available in the breast at the beginning of the breastfeeding. Left and right breasts rarely produced the same volume of milk. The volume of milk consumed by the infant at each breastfeeding depended on whether the breast that was being suckled was the more or less productive breast, whether the breastfeeding was unpaired, or whether it was the first or second breast of paired breastfeedings; the time of day; and whether the infant breastfed during the night or not. Night breastfeedings were common and made an important contribution to the total milk intake. The fat content of the milk was 41.1 ± 7.8 g/L (range: 22.3–61.6 g/L) and was independent of breastfeeding frequency. There was no relationship between the number of breastfeedings per day and the 24-hour milk production of the mothers. CONCLUSIONS. Breastfed infants should be encouraged to feed on demand, day and night, rather than conform to an average that may not be appropriate for the mother-infant dyad.

The yield and nutrient content of colostrum and milk of women from giving birth to 1 month post-partum.

The intake of mammary secretion from delivery to day 5 post-partum was determined by test-weighing nine infants using an integrating electronic balance. The mean yield of colostrum for the first 24 h after birth was 37.1 (range 7.0-122.5) g and was 408 (range 98.3-775) and 705.4 (range 452.5-876) g/24 h on days 3 and 5 post-partum respectively. The milk yield of mothers on either day 14 or 28 post-partum was determined by test-weighing the mother. The mean milk yield was 1.156 (SD 0.167) kg/24 h. A significant correlation (P less than 0.001; r 0.85, n 42) was found between milk yield measured by test-weighing the infant and milk yield measured by test-weighing the mother, confirming that it is possible to obtain a similar estimate of milk consumed using either of the two methods of test-weighing. There was a significant positive correlation (P less than 0.001) between lactose concentration and milk yield for the first 5 d post-partum (r 0.76, n 22); a significant correlation (P less than 0.001) between protein concentration and milk yield (r-0.74, n 22) and no significant correlation between fat concentration and milk yield for the period studied. The calculated energy intake of infants during the first 24 h after birth was only 0.12 (range 0.02-0.29) mJ. This increased to 1.44 (range 0.83-2.18) and 2.99 (range 2.49-4.06) mJ/24 h by days 3 and 14-28 post-partum respectively.

Variation in fat, lactose and protein in human milk over 24 h and throughout the first year of lactation

Fat in human milk is extremely variable and can represent up to 50 % of infant energy intake. To accurately determine milk composition and infant intake at 1 (n 17), 2 (n 17), 4 (n 17), 6 (n 15), 9 (n 6) and 12 (n 5) months of lactation, samples of fore- and hind-milk were collected from each breast at each feed over 24 h periods from an initial group of seventeen women. The content of fat in milk varied over 24 h, with a mean CV of 47.6 (se 2.1) % (n 76) and 46.7 (se 1.7) % (n 76) for left and right breasts respectively. The 24 h amounts of fat, lactose and protein in milk differed between women (P=0.0001), but were consistent between left and right breasts. Daily milk production differed between breasts (P=0.0001) and women (P=0.0001). Accordingly, amounts of fat (P=0.0008), lactose (P=0.0385) and protein (P=0.0173) delivered to the infant over 24 h also differed between breasts and women (P=0.0001). The energy content of milk and the amount of energy delivered to the infant over 24 h were the same between breasts, but differed between women (P=0.0001). The growth rate of a group of only six infants in the present study was not related to either the concentrations or amounts of fat, lactose, protein and energy in milk over the first 6 months of life. These results show the individuality of milk composition and suggest that only a rigorous sampling routine that takes into account all levels of variation will allow the accurate determination of infant intake of fat, lactose, protein and energy.

Anatomy of the lactating human breast redefined with ultrasound imaging

The aim of this study was to use ultrasound imaging to re‐investigate the anatomy of the lactating breast. The breasts of 21 fully lactating women (1–6 months post partum) were scanned using an ACUSON XP10 (5–10 MHz linear array probe). The number of main ducts was measured, ductal morphology was determined, and the distribution of glandular and adipose tissue was recorded. Milk ducts appeared as hypoechoic tubular structures with echogenic walls that often contained echoes. Ducts were easily compressed and did not display typical sinuses. All ducts branched within the areolar radius, the first branch occurring 8.0 ± 5.5 mm from the nipple. Duct diameter was 1.9 ± 0.6 mm, 2.0 ± 90.7 mm and the number of main ducts was 9.6 ± 2.9, 9.2 ± 2.9, for left and right breast, respectively. Milk ducts are superficial, easily compressible and echoes within the duct represent fat globules in breastmilk. The low number and size of the ducts, the rapid branching under the areola and the absence of sinuses suggest that ducts transport breastmilk, rather than store it. The distribution of adipose and glandular tissue showed wide variation between women but not between breasts within women. The proportion of glandular and fat tissue and the number and size of ducts were not related to milk production. This study highlights inconsistencies in anatomical literature that impact on breast physiology, breastfeeding management and ultrasound assessment.

Initiation of Human Lactation: Secretory Differentiation and Secretory Activation

Theories for the origin of milk have been recorded since the time of Ancient Greeks. In those times it was believed that milk was derived from special vessels that connected the uterus to the breasts. The “chyle theory” on the origin of milk was another prominent theory which persisted well into the nineteenth century before the realisation that milk components were derived from blood and some milk constituents were actually synthesized within the breasts. The demonstration that milk ejection was the expulsion of milk that had already been secreted and that milk secretion was a separate continuous process, set the background for the development for the current understanding of milk synthesis and secretion. Today we know that there are two stages in the initiation of lactation- secretory differentiation and secretory activation. Secretory differentiation represents the stage of pregnancy when the mammary epithelial cells differentiate into lactocytes with the capacity to synthesize unique milk constituents such as lactose. This process requires the presence of a ‘lactogenic hormone complex’ of the reproductive hormones, estrogen, progesterone, prolactin and some metabolic hormones. Secretory activation on the other hand, is the initiation of copious milk secretion and is associated with major changes in the concentrations of many milk constituents. The withdrawal of progesterone triggers the onset of secretory activation but prolactin, insulin and cortisol must also be present. This review describes the works of pioneers that have led to our current understanding of the biochemical and endocrinological processes involved in the initiation of human lactation.

Tongue movement and intra-oral vacuum in breastfeeding infants

OBJECTIVE The mechanism by which the breastfeeding infant removes milk from the breast is still controversial. It is unclear whether the infant uses predominantly intra-oral vacuum or a peristaltic action of the tongue to remove milk from the breast. The aim of this study was to use ultrasound to observe movements of the tongue during breastfeeding and relate these movements to both milk flow and simultaneous measurements of intra-oral vacuum. METHODS Submental ultrasound scans of the oral cavity of 20 breastfed infants (3-24 weeks old) were performed during a breastfeed. Intra-oral vacuums were measured simultaneously via a milk-filled supply line (SNS) connected to a pressure transducer. RESULTS Vacuum increased during the downward motion of the posterior tongue and at the same time milk flow and milk ducts in the nipple was observed. Peak vacuum (-145+/-58 mmHg) occurred when the tongue was in the lowest position. CONCLUSIONS Ultrasound imaging demonstrated that milk flow from the nipple into the infants oral cavity coincided with both the lowering of the infants tongue and peak vacuum. Therefore vacuum is likely to play a major role in milk removal from the breast.

Milk Lactose, Citrate, and Glucose as Markers of Lactogenesis in Normal and Diabetic Women

A study was undertaken to define an appropriate marker of lactogenesis II (the onset of copious milk secretion) in mothers, and to determine the effect of diabetes on this marker. Changes in the concentrations of three milk components—lactose, citrate, and glucose—were measured in 38 normal mothers and 6 type I diabetic mothers up to 10 days after birth. Milk yield was measured in 12 of the normal mothers, and all mothers were asked to note the time of milk “coming in” (the feeling of overfullness of the breasts). The average concentrations of lactose, citrate, and glucose in milk were low for the first 24 h after birth, then between 24 and 48 h after birth there was a rapid increase in the concentrations of lactose and citrate, and this transitional period was followed by a plateau period that began between 60 and 84 h after birth. For individual mothers the transitional period for citrate began 32 ± 9 h (n = 13) and finished 77 ± 10 h (n = 17) after birth, and for lactose the transitional period finished at 53 ± 12 h (n = 29) after birth. For diabetic mothers these times were significantly later. The average 24-h milk intake by infants increased from 82 to 556 ml/24 h between 24 and 144 h after birth. Milk intakes were correlated with the concentration of lactose (r = 0.52, n = 51, p < 0.001), citrate (r = 0.47, n = 47, p < 0.001), and glucose (r = 0.69, n = 50, p < 0.001). The time of milk “coming in” was highly variable (59 ± 13) (X ± SD) and occurred well after the onset of copious milk secretion between 24 and 48 h after birth. We conclude that for individual mothers, milk lactose and citrate are useful markers of lactogenesis II. The changes in the concentrations of these markers suggested that lactogenesis II was delayed in type I diabetic mothers.

The effect of supplementation with fish oil during pregnancy on breast milk immunoglobulin A, soluble CD14, cytokine levels and fatty acid composition

Background Breast milk contains many immunomodulatory factors (soluble CD14 (sCD14), IgA and cytokines) with the potential to influence infant immune development.

Exercise intensity and metabolic response in singles tennis

The aim of this study was to determine exercise intensity and metabolic response during singles tennis play. Techniques for assessment of exercise intensity were studied on-court and in the laboratory. The on-court study required eight State-level tennis players to complete a competitive singles tennis match. During the laboratory study, a separate group of seven male subjects performed an intermittent and a continuous treadmill run. During tennis play, heart rate (HR) and relative exercise intensity (72 +/- 1.9% VO2max; estimated from measurement of heart rate) remained constant (83.4 +/- 0.9% HRmax; mean +/- s(x)) after the second change of end. The peak value for estimated play intensity (1.25 +/- 0.11 steps x s(-1); from video analysis) occurred after the fourth change of end (P< 0.005). Plasma lactate concentration, measured at rest and at the change of ends, increased 175% from 2.13 +/- 0.32 mmol x l(-1) at rest to a peak 5.86 +/- 1.33 mmol x l(-1) after the sixth change of end (P < 0.001). A linear regression model, which included significant terms for %HRmax (P< 0.001), estimated play intensity (P < 0.001) and subject (P < 0.00), as well as a %HRmax subject interaction (P < 0.05), accounted for 82% of the variation in plasma lactate concentration. During intermittent laboratory treadmill running, % VO2peak estimated from heart rate was 17% higher than the value derived from the measured VO2 (79.7 +/- 2.2% and 69.0 +/- 2.5% VO2peak respectively; P< 0.001). The %VO2peak was estimated with reasonable accuracy during continuous treadmill running (5% error). We conclude that changes in exercise intensity based on measurements of heart rate and a time-motion analysis of court movement patterns explain the variation in lactate concentration observed during singles tennis, and that measuring heart rate during play, in association with preliminary fitness tests to estimate VO2, will overestimate the aerobic response.

Blood and milk prolactin and the rate of milk synthesis in women

In women, the concentration of prolactin in the plasma increases in response to nipple stimulation. This response has led to the assumption that prolactin influences the rate of milk synthesis. To investigate this hypothesis we have measured 24 h milk production, the short‐term (between breastfeeds) rates of milk synthesis and the concentration of prolactin in the blood and breastmilk, from 1 to 6 months of lactation in eleven women. Over the long term, the 24 h milk production remained constant (means +/− S.E.M.): 708 +/− 54.7 g/24 h (n = 11) and 742 +/− 79.4 g/24 h (n = 9) at 1 and 6 months, respectively. The average short‐term rate of milk synthesis (calculated from the increase in breast volume between breastfeeds; means +/− S.E.M.) did not change: 23 +/− 3.5 ml/h (n = 23) and 23 +/− 3.4 ml/h (n = 21) at 1 and 6 months, respectively. However, significant variation in the short‐term rate of milk synthesis (from < 5.8 to 90 ml/h) was found both between breasts, measured concurrently (coefficient of variation, c.v. = 72%), and within the same breast, measured over consecutive breastfeeds (c.v. = 85%). The basal and suckling‐stimulated concentrations of prolactin in the plasma (means +/− S.E.M.) declined from 1 to 6 months (basal, from 119 +/− 93 to 59 +/− 29 micrograms/1; peak, from 286 +/− 109 to 91 +/− 44 micrograms/l). In contrast, the concentration of prolactin in milk was much lower than in plasma, and decreased only slightly from 1 to 6 months of lactation (fore‐milk, from 26.4 +/− 10 to 23.3 +/− 9.8 micrograms/l; hind‐milk, from 18.9 +/− 5.1 to 13.2 +/− 6.3 micrograms/l). The concentration of prolactin in the milk was related to the degree of fullness of the breast, such that the concentration was highest when the breast was full. We found no relationship between the concentration of prolactin in the plasma and the rate of milk synthesis in either the short or long term. However, the relationship between the concentration of prolactin in milk and the degree of fullness of the breast suggests that the internalization of prolactin, after binding to its receptor, may be restricted when the alveolus is distended with milk.