Breast milk feeding, brain development, and neurocognitive outcomes: a 7-year longitudinal study in infants born <30 weeks’ gestation

Abstract

Objectives

To determine the associations of breast milk intake after birth with neurological outcomes at term equivalent and 7 years of age in very preterm infants

Study design

We studied 180 infants born <30 weeks’ gestation or <1250 grams birth weight enrolled in the Victorian Infant Brain Studies cohort from 2001–2003. We calculated the number of days on which infants received >50% of enteral intake as breast milk from 0–28 days of life. Outcomes included brain volumes measured by magnetic resonance imaging at term equivalent and 7 years of age, and cognitive (IQ, reading, mathematics, attention, working memory, language, visual perception) and motor testing at years. We adjusted for age, sex, social risk,7 and neonatal illness in linear regression.

Results

A greater number of days on which infants received >50% breast milk was associated with larger deep nuclear gray matter volume at term equivalent age (0.15 cc/day, 95% CI 0.05, 0.25); and with better performance at age 7 years on IQ (0.5 points/day, 95% CI 0.2, 0.8), mathematics (0.5, 95% CI 0.1, 0.9), working memory (0.5, 95% CI 0.1, 0.9), and motor function (0.1, 95% CI 0.0, 0.2) tests. No differences in regional brain volumes at 7 years in relation to breast milk intake were observed.

Conclusion

Predominant breast milk feeding in the first 28 days of life was associated with larger deep nuclear gray matter volume at term equivalent age and better IQ, academic achievement, working memory, and motor function at 7 years of age in very preterm infants.

In healthy, full term populations, breastfeeding appears beneficial to neurodevelopment.^1–3 One proposed mechanism linking breastfeeding with brain development is the effect of specific nutrients in breast milk that are either absent from or present in lower amounts in infant formula.⁴ Another potential mechanism is through greater sensitivity to the infant shown by mothers who provide breast milk,⁵ because maternal sensitivity is associated with better neurodevelopment.⁶ Connections between breastfeeding and infant development may also be explained in part by shared social determinants such as maternal educationand family income, and maternal IQ.⁷

The effects of breast milk and breastfeeding on neurodevelopment may be quite different in very preterm infants than in those born full term. Nutritionally, breast milk is considered the optimal food for full term infants, but preterm infants require fortification to match 3^rd trimester nutrient accretion rates.⁸ Even with fortification, weight gain of breast milk-fed infants lags behind that of infants fed preterm formula,^{9, 10} suggesting possible undernutrition. In hospitalized very preterm infants, feedings are typically given via tube rather than directly at the breast, thereby uncoupling the ingestion of breast milk from the maternal interactions that occur during the act of breastfeeding. However, the time invested in expressing and delivering breast milk may reflect different levels of attachment or sensitivity. Given these differences between preterm and term infants, focused research needed to evaluate the potential benefits of breast milk intake on the neurodevelopment of very preterm infants.

Direct imaging of the brain may shed light on mechanisms linking breast milk, brain growth, and neurodevelopment. In full term infants, magnetic resonance imaging (MRI) of the brain demonstrated greater white matter development from 10 months to 4 years¹¹ and at 8 years¹²; and greater cortical thickness in adolescence¹³ in relation to early breastfeeding exposure. In preterm infants, one small study¹⁴ (n=50) found positive correlations of breast milk intake with total brain volume at 15 years of age. Another study¹⁵ of preterm infants reported that greater breast milk intake was associated with improved corpus callosum maturation at term equivalent age (40 weeks postmenstrual age), but infants were not followed beyond neonatal discharge. Additional research is needed to determine the extent to which breast milk intake during the neonatal period affects the preterm infant brain and whether effects persist beyond the newborn period.

Our aims in this study were to examine associations of breast milk intake during the neonatal hospitalization with brain MRI characteristics at term equivalent and 7 years of age and neurodevelopmental outcomes at 2 and 7 years of age.

Methods

We studied participants in the Victorian Infant Brain Studies (VIBeS) longitudinal cohort. 224 infants born <30 weeks’ gestation or <1250 grams birth weight were enrolled before term equivalent age at the Royal Women’s Hospital in Melbourne, Australia between July 2001 and December 2003. Exclusion criteria included congenital anomalies likely to affect brain development or function. Parents provided informed consent for their children to participate. The Royal Women’s Hospital and Royal Children’s Hospital institutional review boards approved the study. For this analysis, we excluded 44 participants due to missing breast milk data. The remaining 180 participants had available data for at least one outcome (n=160 with term equivalent brain MRI; n=173 with 2 year Bayley testing; n=108 with 7 year brain MRI; and n=161 with 7 year neurocognitive testing) and were included in the present analysis.

Breast milk intake

Study staff abstracted the daily volume of breast milk and formula intake for the first 28 days of life from the medical record. We focusedon breast milk intake in the first 28 days with the goal of minimizing attrition due to early transfer or discharge that could bias results. In a subset of 20 randomly selected participants, we abstracted data on breast milk intake (mL/kg/day) through day 40, and found a strong correlation with intake from birth to 28 days (Pearson r=0.95). Breast milk was fortified according to unit-based practice. Preterm formula was used when a mother’s own breast milk was unavailable or in short supply; donor breast milk was not used.

Brain magnetic resonance imaging (MRI) at term equivalent and 7 years

At term equivalent age (range, 38 to 42 weeks postmenstrual age), participants underwent brain MRI in a 1.5T General Electric scanner (Signa Echospeed System; Milwaukee, WI, USA). Infants were fed, swaddled, and placed in a supportive beanbag. No analgesia or sedation was given. T₁ and T2/proton density weighted images were acquired.¹⁶ Structural images were semi-automatically segmented into white matter (unmyelinated, myelinated), cortical gray matter, deep nuclear gray matter (including basal ganglia and thalamus) and cerebrospinal fluid.^{17, 18} Hippocampi and cerebella were manually traced.^{19, 20}

At 7 years (range, 6.6 to 8.1 years), participants again underwent brain MRI. Children were scanned on a 3 Tesla Siemens Magnetom Trio scanner, with T₁ weighted images acquired (0.85mm sagittal slices, flip angle = 9°, repetition time = 1900ms, echo time = 2.27ms, field of view = 210 × 210mm, matrix= 256 × 256). Brain volumes were obtained using FreeSurfer, an automated imaging processing package (stable release version 4.4.0, http://surfer.nmr.mgh.harvard.edu), with manual editing as required. Cortical and cerebellar gray and white matter, deep nuclear gray matter (thalamus, nucleus accumbens, caudate, putamen, pallidum) were estimated and volumes combined from both hemispheres. Cerebellar volume was calculated as the total cerebellar white plus gray matter. Total brain volume was the combined volumes of all brain structures. Hippocampi were manually traced.²¹

Neurodevelopmental assessments at 2 and 7 years

Trained examiners administered the Bayley Scales of Infant Development, 2^nd edition (Bayley-2) when children were 2 years corrected age. The Bayley-2 comprises the Mental Development Index (MDI), which measures cognition, and the Psychomotor Development Index (PDI), which measures motor skills. Domains tested at 7 years included: general intelligence (Wechsler Abbreviated Scale of Intelligence, WASI)²²; academic achievement (Word Reading and Math Computation subtests of the Wide Range Achievement Test, WRAT4)²³; attention (Score subtest of the Test of Every Day Attention for Children, TEA-Ch)²⁴; working memory (Backward Digit Recall subtests of the Working Memory Test Battery for Children, WMTBC)²⁵; language (Core Language Index from the Clinical Evaluation of Language Fundamentals, CELF-IV)²⁶; visual perception (Visual Closure subtest of the Test of Visual Perceptual Skills, TVPS-3)²⁷; and motor function (Movement Assessment Battery for Children, MABC2)²⁸. Higher scores on all of these measures indicate better performance. Scores from the Bayley-2, WASI, WRAT4, WMTBC, and CELF-IV were age-standardized to a mean of 100 and standard deviation (SD) 15; the remaining tests were standardized to a mean of 10 (SD 3). We used corrected age for all scores. On the Bayley-2, children who fell below the basal threshold for testing were assigned a score of 45; children too impaired for testing were assigned a score of 40.

Covariates

Infant sex, gestational age, exposure to antenatal or postnatal corticosteroids, supplemental oxygen requirement at 36 weeks, and diagnosis of sepsis or necrotizing enterocolitis were abstracted from the medical record. The Clinical Risk Index for Babies (CRIB) score is an illness severity indicator.²⁹ We calculated a social risk score comprising: maternal age, parent marital status, education level of baby’s primary caregiver, employment status and income of primary income earner, and language spoken at home.³⁰ Participants were categorized as being of lower (score, 0 or 1) or higher (score, 2 or higher) social risk. Using infant weight obtained with a digital scale at birth and at the time of the term equivalent MRI, we calculated the weight z-score change from birth to term equivalent age.³¹

Statistical Analyses

We calculated 2 measures of breast milk intake: number of days on which the infant received >50% of enteral intake as breast milk and mean daily breast milk intake (mL/kg/day). Main outcomes were regional brain volumes (term equivalent and 7 years of age) and neurodevelopmental test scores (2 and 7 years of age). We estimated associations between exposures and outcomes in linear regression, fitted using generalized estimating equations with an exchangeable correlation structure to account for clustering due to multiple births. In Model 0, we adjusted for the child’s sex, exact age at scan or assessment, and gestational age at birth. In Model 1, we additionally adjusted for social risk score (higher vs. lower), and in Model 2 we additionally included variables that reflect neonatal illness severity. In Model 3 we included neonatal weight gain (a proxy for nutritional adequacy) to explore its mediating effect, hypothesizing that adjusting for weight z-score change from birth to term would strengthen associations of breast milk intake with outcomes, given associations of breast milk intake with slower weight gain⁹ and slower weight gain with poorer developmental outcomes.^{32, 33}

Results

Table I shows characteristics of our participants, who had rates of perinatal complications and long-term outcomes typical of their immaturity [mean (SD) gestational age, 27.3 (1.8) weeks] at birth. The mean number of days from day 0–28 on which infants received breast milk as >50% of their feedings was 21 (SD 7). Mean breast milk intake in the first 28 days was 90 (SD 43) mL/kg/day. Multiple gestations comprised 45% of the cohort. As compared with singletons, mean breast milk intake for multiples was slightly lower (86 mL/kg/day).

Table 1.

Patient characteristics (n=180)

	Mean (SD)
Gestational age at birth, weeks	27.3 (1.8)
Birth weight, grams	947 (210)
Weight z-score change, birth to term	−1 (1.5)
	Median (IQR)
Clinical Risk Index for Babies28 score	3 (1, 6)
	Number (percent)
Sex
Male	88 (49%)
Female	92 (51%)
Multiple gestation	81 (45%)
Antenatal corticosteroids	162 (91%)
Neonatal illness
Supplemental oxygen dependency at 36 weeks*	61 (34%)
Postnatal corticosteroids	17 (9%)
Sepsis (proven or suspected)	66 (37%)
Necrotizing enterocolitis	20 (11%)
Social risk score29
Low	63 (40%)
High	94 (60%)
	Mean (SD)
Number of days breast milk >50%, 0–28 days	21 (7)
Mean breast milk intake, 0–28 days	90 (43)
Brain volumes at term equivalent, cc
Intracranial volume	441 (67)
Total brain volume	394 (58)
Total gray matter	157 (39)
Total white matter	223 (31)
Myelinated white matter	9.8 (4.6)
Unmyelinated white matter	213 (31)
Deep nuclear gray matter	13.4 (3.8)
Cerebellum	21.2 (3.8)
Hippocampus	2.2 (0.3)
Bayley-2 Scores at 2 years corrected age
Mental Development Index	84 (20)
Psychomotor Development Index	88 (17)
Brain volumes at 7 years, cc
Intracranial volume	1326 (118)
Total brain volume	1258 (112)
Total gray matter	783 (68)
Total white matter	400 (45)
Deep nuclear gray matter	36.3 (3.2)
Cerebellum	147 (14)
Hippocampus	6.5 (0.7)
Neurodevelopment at 7 years
General intelligence (WASI)
Full scale IQ	97 (14)
Performance IQ	97 (14)
Verbal IQ	96 (14)
Word Reading (WRAT4)	99 (19)
Math Computations (WRAT4)	89 (17)
Attention (TEA-Ch)	7.6 (3.6)
Working memory (WMTBC)	87 (16)
Language (CELF-IV)	92 (17)
Visual perception (TVPS-3)	8.3 (3.6)
Motor function (MABC2)	8.6 (3.5)

SD is standard deviation. WASI is Weschler Abbreviated Scale of Intelligence²¹; WRAT4 is Wide Range Achievement Test²²; TEA-Ch is Test of Every Day Attention for Children²³; WMTBC is Working Memory Test Battery for Children²⁴; CELF-IV is Clinical Evaluation of Language Fundamentals²⁵; TVPS-3 is Test of Visual Perceptual Skills²⁶; and MABC2 is Movement Assessment Battery for Children²⁷. Higher scores on all of these measures indicate better performance.

^*Did not receive postnatal corticosteroids

Table II shows the linear associations of the estimated brain volumes at term equivalent with the number of days on which breast milk comprised >50% of enteral intake during the first 28 days of life. In a model adjusted only for age, sex, and gestational age at birth (Model 0), for each additional day of breast milk >50% of intake, the deep nuclear gray matter volume was 0.11 cc/day [95% confidence interval (CI), 0.02, 0.20] larger. This association persisted after additional adjustment for social risk score (Model 1) and markers of neonatal illness (Model 2, 0.15 cc/day, 95% CI 0.05, 0.25). Additionally adjusting for neonatal weight gain (Model 3) did not change these estimates. Other brain volumes were not substantially associated with days of breast milk intake >50% (Table II). In Table III (available at www.jpeds.com), we show associations of average daily breast milk intake on day 0–28 with brain volumes at term, with evidence for a relationship with hippocampal volume (0.02 cc per 10 mL/kg/day breast milk, 95% CI 0.01, 0.03) that persisted after adjustment for covariates. Associations of average daily breast milk intake with other brain volumes appeared minimal (Table III).

Table 2.

Number of days on which enteral intake was >50% breast milk and estimated brain volumes at term equivalent age

	Model 0 n=147		Model 1 n=133		Model 2 n=132		Model 3 n=131
	β indicates cc increment in estimated brain volume per 1 additional day on which breast milk was >50% of enteral intake during the first 28 days of life
	β	95% CI	β	95% CI	β	95% CI	β	95% CI
Intracranial volume	−0.05	−2.05, 1.05	−0.22	−1.93, 1.50	−0.42	−1.84, 0.99	−0.30	−1.57, 0.97
Total brain size	−0.07	−1.36, 1.22	0.18	−1.25, 1.61	0.00	−1.21, 1.21	0.06	−1.06, 1.17
Total gray matter	−0.29	−1.12, 0.55	−0.20	−1.12, 0.73	−0.32	−1.17, 0.53	−0.29	−1.11, 0.52
Total white matter	0.10	−0.58, 0.77	0.20	−0.54, 0.94	0.17	−0.48, 0.82	0.19	−0.42, 0.81
Myelinated white matter	−0.01	−0.10, 0.09	−0.03	−0.12, 0.07	−0.03	−0.12, 0.07	−0.02	−0.12, 0.07
Unmyelinated white matter	0.10	−0.56, 0.76	0.21	−0.52, 0.94	0.17	−0.46, 0.81	0.19	−0.41, 0.79
Deep nuclear gray matter	0.11	0.02, 0.20	0.14	0.05, 0.23	0.15	0.05, 0.25	0.15	0.05, 0.25
Cerebellum	0.03	−0.07, 0.12	0.04	−0.06, 0.15	0.03	−0.07, 0.12	0.03	−0.06, 0.11
Hippocampus	0.003	−0.004, 0.01	0.003	−0.01, 0.01	0.001	−0.01, 0.01	0.002	−0.01, 0.01

CI is confidence interval.

Model 0 is adjusted for exact age at assessment, gender, gestational age at birth

Model 1 = Model 0 + social risk score

Model 2 = Model 1 + multiple gestation, Clinical Risk Index for Babies score, antenatal or postnatal corticosteroids, neonatal illness (supplemental oxygen dependency at 36 weeks, sepsis or necrotizing enterocolitis)

Model 3 = Model 2 + birth-to-term weight z-score change

Table 3.

Average breast milk intake in the first 28 days of life and brain volumes at term equivalent and 7 years of age

	Model 0 (n=96)	Model 1 (n=85)	Model 2 (n=84)	Model 3 (n=84)
	β (95% confidence interval) indicates estimated cc increment in brain volume per additional 10 mL average breast milk intake in the first 28 days of life
Term equivalent
Intracranial volume	0.01 (−2.78, 2.80)	0.81 (−2.24, 3.87)	0.13 (−2.49, 2.76)	−0.28 (−2.74, 2.18)
Total brain size	0.89 (−1.40, 3.17)	1.54 (−0.87, 3.95)	1.33 (−0.76, 3.42)	1.12 (−0.88, 3.12)
Total gray matter	−0.02 (−1.48, 1.44)	0.06 (−1.48, 1.61)	0.71 (−0.64, 2.07)	0.65 (−0.76, 2.06)
Total white matter	0.60 (−0.85, 2.05)	0.97 (−0.64, 2.57)	0.77 (−0.64, 2.19)	0.70 (−0.69, 2.08)
Myelinated white matter	−0.07 (−0.25, 0.11)	−0.09 (−0.27, 0.10)	−0.10 (−0.27, 0.07)	−0.11 (−0.28, 0.05)
Unmyelinated white matter	0.67 (−0.78, 2.12)	1.06 (−0.54, 2.65)	0.88 (−0.53, 2.29)	0.82 (−0.57, 2.21)
Deep nuclear gray matter	0.06 (−0.11, 0.23)	0.12 (−0.05, 0.29)	0.14 (−0.03, 0.30)	0.13 (−0.03, 0.29)
Cerebellum	0.08 (−0.05, 0.22)	0.10 (−0.05, 0.25)	0.08 (−0.05, 0.21)	0.06 (−0.05, 0.17)
Hippocampus	0.02 (0.002, 0.03)	0.02 (0.01, 0.04)	0.02 (0.004, 0.03)	0.02 (0.003, 0.03)
7 years
Intracranial volume	1.72 (−3.87, 7.32)	1.96 (−3.74, 7.66)	1.60 (−4.11, 7.31)	1.93 (−3.97, 7.82)
Total brain size	0.33 (−5.14, 5.81)	0.54 (−4.89, 5.96)	0.12 (−5.70, 5.93)	0.43 (−5.54, 6.41)
Total gray matter	0.19 (−3.48, 3.86)	0.42 (−3.10, 3.94)	−2.45 (−7.62, 2.72)	−0.35 (−4.83, 4.12)
Total white matter	0.09 (−2.14, 2.32)	0.06 (−2.16, 2.28)	0.16 (−1.99, 2.32)	0.17 (−2.05, 2.40)
Deep nuclear gray matter	−0.01 (−0.15, 0.14)	−0.01 (−0.16, 0.15)	0.00 (−0.15, 0.15)	−0.01 (−0.17, 0.14)
Cerebellum	−0.30 (−0.94, 0.33)	−0.31 (−0.95, 0.33)	−0.25 (−0.84, 0.35)	−0.34 (−0.97, 0.29)
Hippocampus	0.01 (−0.02, 0.04)	0.00 (−0.03, 0.04)	0.00 (−0.03, 0.03)	−0.00 (−0.04, 0.03)

CI is confidence interval

Model 0 is adjusted for exact age at assessment, gender, gestational age at birth

Model 1 = Model 0 + social risk score

Model 2 = Model 1 + multiple gestation, Clinical Risk Index for Babies score, antenatal or postnatal corticosteroids, neonatal illness (supplemental oxygen dependency at 36 weeks, sepsis or necrotizing enterocolitis)

Model 3 = Model 2 + birth-to-term weight z-score change

In Table IV, we show associations of breast milk intake with estimated brain volumes at 7 years. With adjustment for age, sex, and gestational age, the intracranial volume was larger (2.67 cc/day that breast milk >50% of intake, 95% CI 0.37, 4.97). With adjustment for social risk and neonatal illness, the estimate remained similar (2.42 cc/day), but the 95% CI included 0 (−0.19, 5.04). We also observed a small association with hippocampal volume that was attenuated with covariate adjustment (Table IV). There was little evidence of associations between average daily breast milk intake and other regional brain volumes at 7 years (Table III).

Table 4.

Number of days on which enteral intake was >50% breast milk and estimated brain volumes at 7 years of age

	Model 0 n=108		Model 1 n=104		Model 2 n=103		Model 3 n=102
	β indicates cc increment in estimated brain volume per 1 additional day on which breast milk was >50% of enteral intake during the first 28 days of life
	β	95% CI	β	95% CI	β	95% CI	β	95% CI
Intracranial volume	2.67	0.37, 4.97	2.67	0.23, 5.10	2.42	−0.19, 5.04	2.43	−0.18, 5.04
Total brain size	2.04	−0.06, 4.15	1.94	−0.32, 4.20	1.77	−0.86, 4.39	1.78	−0.86, 4.41
Total gray matter	1.44	−0.20, 3.07	1.39	−0.32, 3.10	0.94	−1.13, 3.01	0.94	−1.15, 3.03
Total white matter	0.52	−0.20, 1.23	0.49	−0.25, 1.23	0.52	−0.38, 1.42	0.53	−0.38, 1.44
Deep nuclear gray matter	0.04	−0.03, 0.11	0.03	−0.04, 0.10	−0.01	−0.10, 0.07	−0.01	−0.10, 0.07
Cerebellum	0.09	−0.23, 0.40	0.08	−0.26, 0.41	−0.13	−0.48, 0.23	−0.13	−0.49, 0.23
Hippocampus	0.01	0.002, 0.03	0.01	−0.002, 0.03	0.01	−0.01, 0.03	0.01	−0.01, 0.03

CI is confidence interval.

Model 0 is adjusted for exact age at assessment, gender, gestational age at birth

Model 1 = Model 0 + social risk score

Model 2 = Model 1 + multiple gestation, Clinical Risk Index for Babies score, antenatal or postnatal corticosteroids, neonatal illness (supplemental oxygen dependency at 36 weeks, sepsis or necrotizing enterocolitis)

Model 3 = Model 2 + birth-to-term weight z-score change

There was also little evidence of associations between breast milk intake and Bayley scores at 2 years (Table V). Regarding 7 year outcomes, in Model 0, the full scale IQ was 0.5 points (95% CI 0.3, 0.8) higher for each additional day of breast milk intake >50%; estimates were similar with additional adjustment for covariates (Models 1–3). A similar pattern was observed for Verbal and Performance IQ, Math Computation, and Working Memory. Motor functioning was also higher with increasing days of breast milk >50% in covariate-adjusted models (Table IV), for example 0.1 points/day, 95% CI 0.03, 0.2 after adjustment for social risk and neonatal illness factors (Model 2). In Table VI (available at www.jpeds.com), we show similar associations of full scale IQ with average daily breast milk intake (0.7 points per 10 mL/kg/day, 95% CI 0.1, 1.3) that attenuated slightly with covariate adjustment. Positive associations of average daily breast milk intake with Working Memory were also noted, whereas greater breast milk intake was associated with lower Visual Perception scores (−0.2 points per 10 mL/kg/day, 95% CI −0.3, – 0.03 in Model 2) (Table VI).

Table 5.

Number of days on which enteral intake was >50% breast milk and neurodevelopmental outcomes at 2 and 7 years of age

	N	Model 0 n=150		Model 1 n=140		Model 2 n=136		Model 3 n=136
		β indicates increment in test points per 1 additional day on which breast milk was >50% of enteral intake during the first 28 days of life
		β	95% CI	β	95% CI	β	95% CI	β	95% CI
2 Years
Bayley MDI	173	0.3	−0.2, 0.8	0.4	−0.1, 0.9	0.4	−0.1, 1.0	0.4	−0.1, 1.0
Bayley PDI	173	0.1	−0.3, 0.6	0.1	−0.3, 0.6	0.1	−0.4, 0.6	0.1	−0.4 0.6
7 Years
General intelligence (WASI)
Full scale IQ	154	0.5	0.3, 0.8	0.5	0.2, 0.8	0.5	0.2, 0.8	0.5	0.2, 0.8
Verbal IQ	156	0.4	0.1, 0.7	0.4	0.1, 0.7	0.4	0.1, 0.7	0.4	0.1, 0.8
Performance IQ	155	0.5	0.2, 0.8	0.5	0.2, 0.8	0.5	0.2, 0.8	0.5	0.2, 0.7
Word Reading (WRAT4)	153	0.5	−0.03, 0.9	0.4	−0.1, 0.9	0.5	−0.03, 1.0	0.5	−0.03, 1.0
Math Computations (WRAT4)	152	0.6	0.2, 0.9	0.5	0.1, 0.9	0.5	0.1, 0.9	0.5	0.1,1.0
Attention (TEA-Ch)	148	0.1	−0.04, 0.2	0.1	−0.1, 0.2	0.02	−0.1, 0.1	0.02	−0.1, 0.1
Working memory (WMTBC)	144	0.5	0.1, 0.8	0.4	0.1, 0.8	0.5	0.1, 0.9	0.5	0.1, 0.9
Language (CELF-IV)	149	0.5	−0.03, 1.0	0.4	−0.1, 1.0	0.4	−0.1, 1.0	0.5	−0.1, 1.0
Visual perception (TVPS-3)	142	0.03	−0.1, 0.1	0.01	−0.1, 0.1	−0.03	−0.1, 0.09	−0.01	−0.1, 0.1
Motor function (MABC2)	136	0.1	−0.001, 0.2	0.1	−0.01, 0.2	0.1	0.02, 0.2	0.1	0.03, 0.2

CI is confidence interval.

Numbers in multivariable models are slightly lower due to missing covariate data. Exact numbers are available upon request.

WASI is Weschler Abbreviated Scale of Intelligence²¹; WRAT4 is Wide Range Achievement Test²²; TEA-Ch is Test of Every Day Attention for Children²³; WMTBC is Working Memory Test Battery for Children²⁴; CELF-IV is Clinical Evaluation of Language Fundamentals²⁵; TVPS-3 is Test of Visual Perceptual Skills²⁶; and MABC2 is Movement Assessment Battery for Children²⁷. Higher scores indicate better performance.

Model 0 is adjusted for exact age at assessment, gender, gestational age at birth

Model 1 = Model 0 + social risk score

Model 2 = Model 1 + multiple gestation, Clinical Risk Index for Babies score, antenatal corticosteroids, neonatal illness (chronic lung disease, sepsis, necrotizing enterocolitis)

Model 3 = Model 2 + birth-to-term weight z-score change

Table 6.

Average breast milk intake in the first 28 days of life and neurodevelopmental outcomes at 2 and 7 years of age

		Model 0	Model 1	Model 2	Model 3
	N	β (95% confidence interval) indicates estimated increment in test points per additional 10 mL average breast milk intake in the first 28 days of life
2 Years
Bayley MDI	116	0.4 (−0.5, 1.3)	0.5 (−0.3, 1.2)	0.4 (−0.3, 1.2)	0.5 (−0.3, 1.2)
Bayley PDI	116	−0.02 (−0.7, 0.7)	0.2 (−0.5, 0.8)	−0.01 (−0.6, 0.6)	−0.1 (−0.6, 0.5)
7 Years
General intelligence (WASI)
Full scale IQ	105	0.7 (0.1, 1.3)	0.7 (0.1, 1.3)	0.7 (0.1, 1.3)	0. 7 (0.1, 1.2)
Verbal IQ	105	0.5 (−0.1, 1.1)	0.6 (−0.02, 1.2)	0.5 (−0.03, 1.1)	0.6 (0.02, 1.2)
Performance IQ	106	0.6 (−0.002, 1.2)	0.5 (−0.1, 1.2)	0.6 (−0.1, 1.1)	0.5 (−0.1, 1.0)
Word Reading (WRAT4)	103	0.2 (−0.5, 0.9)	0.2 (−0.6, 1.0)	0.2 (−0.6, 0.9)	0.3 (−0.5, 1.0)
Math Computations (WRAT4)	103	0.7 (0.002, 1.4)	0.6 (−0.1, 1.4)	0. 6 (−0.2, 1.3)	0.5 (−0.2, 1.3)
Attention (TEA-Ch)	99	0.1 (−0.1, 0.3)	0.08 (−0.1, 0.3)	0.1 (−0.2, 0.3)	0.04 (−0.2, 0.2)
Working memory (WMTBC)	97	0.9 (0.1, 1.7)	0. 8 (0.1, 1.5)	0.8 (0.1, 1.5)	0.8 (0.1, 1.6)
Language (CELF-IV)	100	0.1 (−0.7, 0. 8)	0.1 (−0.7, 0.8)	0.1 (−0.7, 0.8)	0.1 (−0. 6, 0.8)
Visual perception (TVPS-3)	100	−0.1 (−0.3, 0.01)	−0.1 (−0.3, 0.01)	−0.2 (−0.3, −0.03)	−0.2 (−0.3, −0.04)
Motor ability (MABC2)	93	0.1 (−0.02, 0.3)	0.1 (−0.03, 0.3)	0.1 (−0.0, 0.3)	0.1 (−0.01, 0.3)

CI is confidence interval.

Numbers in multivariable models are slightly lower due to missing covariate data. Exact numbers are available upon request.

WASI is Weschler Abbreviated Scale of Intelligence²¹; WRAT4 is Wide Range Achievement Test²²; TEA-Ch is Test of Every Day Attention for Children²³; WMTBC is Working Memory Test Battery for Children²⁴; CELF-IV is Clinical Evaluation of Language Fundamentals²⁵; TVPS-3 is Test of Visual Perceptual Skills²⁶; and MABC2 is Movement Assessment Battery for Children²⁷. Higher scores indicate better performance.

Model 0 is adjusted for exact age at assessment, gender, gestational age at birth

Model 1 = Model 0 + social risk score

Model 2 = Model 1 + multiple gestation, Clinical Risk Index for Babies score, antenatal or postnatal corticosteroids, neonatal illness (supplemental oxygen dependency at 36 weeks, sepsis or necrotizing enterocolitis)

Model 3 = Model 2 + birth-to-term weight z-score change

Discussion

In a contemporary cohort of 180 very preterm infants, we found favorable associations of maternal breast milk intake in the first 28 days of life with neurodevelopmental outcomes at 7 years of age. For example, IQ was 0.5 points higher per additional day that breast milk intake was over 50% of total enteral intake, and 0.7 points higher per additional 10 mL/kg/day breast milk ingested. Even if residual confounding explains some of this effect, our results nonetheless suggest a substantial impact of breast milk intake in the first month of life on very preterm infant neurodevelopment assessed at school age. We also saw associations of breast milk intake with size of the deep nuclear gray matter and hippocampus at term equivalent age, although this effect was not present on brain volumes assessed at age 7 years.

Previous studies supporting the beneficial effects of breast milk intake on neurodevelopment in very preterm infants have examined infant or toddler outcomes,^{10, 34, 35} which have limitations in the prediction of later cognitive abilities.^{36, 37} Assessment at school age as in the current study also allows for more detailed measurement of cognitive functioning, including memory, attention, and school achievement. These domains are particularly important to assess in very preterm infants, who are prone to difficulties in these areas.^38–41

We identified only 2 studies^{42, 43} of very preterm or very low birth weight (VLBW, <1500 grams) infants born in 1990 or beyond that examined breast milk intake or breastfeeding in relation to school age neurodevelopmental measures, as we did in this study. An analysis⁴² of data from the EPIPAGE cohort of French infants <33 weeks’ gestation found that the risk of non-optimal neurodevelopment at age 5 years was substantially lower (odds ratio 0.7, 95% CI 0.5, 0.9) for infants who were breastfeeding at the time of neonatal discharge vs. not. A notable limitation of the EPIPAGE study was the method of categorizing infants based on any versus no breast milk at the time of discharge. That method could have led to an underestimation of the effect size if many of the infants who received breast milk early in the hospitalization were no longer receiving it at discharge. In contrast, we had detailed data about the amount of breast milk ingested during the first 28 days of life. Additionally, EPIPAGE⁴² used as their outcome measure the Kaufman Assessment Battery for Children Mental Processing Composite, which reflects general intelligence. In addition to measures of IQ, our study found evidence of associations between breast milk intake and measures of word reading and mathematics, working memory, and motor function. Overall, it appears that greater exposure to breast milk is associated not only with higher general intelligence, but also with better academic achievement, memory, and motor function in children who were born very preterm.

In contrast to our results, a U.S. study⁴³ of VLBW infants showed no advantages of feeding expressed breast milk or directly breast feeding through 6 months of age on a battery of tests at 6–8 years of age, including general intelligence, verbal ability, fine motor skills, and visual-spatial skills, and a small advantage on visual motor skill tests. A major difference from our study was their reliance on parental report of breastfeeding type and duration (<1 week, 1–4 weeks, 4–6 months, 6 or more months), whereas we used the medical record to quantify the volume of breast milk ingested in the first 28 days of the neonatal hospitalization. It is possible that the preterm brain is more sensitive to the beneficial effects of breast milk earlier in development, specifically prior to term when developmental processes such as dendritic and axonal growth and synaptogenesis are ongoing and distinct from the processes that predominate after term, such as pruning and myelination.

In our study, there was little statistical evidence for associations between breast milk intake and Bayley scores at 2 years of age. However, the effect estimate for the MDI (0.4 points per day receiving >50% breast milk) was similar in magnitude to our estimate for IQ at 7 years (0.5 points per day), with more variability in estimates at 2 than at 7 years. In a larger (~1000 participants) U.S. cohort⁴⁴ of extremely low birth weight (<1000 grams) infants, for every 10 mL/kg average daily breast milk intake, the MDI at 18 months was 0.5 points higher; our results were similar in magnitude (0.4 points higher). Some¹⁰ but not all^{34, 45} previous studies have found similar results with outcomes measured in infancy through preschool age. Our study is unique in that we assessed the same children both at 2 and 7 years of age. In a previous analysis² of full term children who underwent cognitive assessment at 3 and 7 years, we found beneficial effects of greater duration and exclusivity of breastfeeding on cognition at 7 but not 3 years of age. It is possible that assessment early in childhood is too soon to detect subtle effects of breast milk that are more evident at school age. It is also possible that the influence of the shared determinants of breastfeeding and neurodevelopment – such as environmental, social, and economic factors – increases over time.

Another feature of our study was the analysis of regional brain volumes in relation to early breast milk intake in very preterm infants. In particular, we found that a greater dose of breast milk (more days on which breast milk comprised >50% of intake) was associated with larger deep nuclear gray matter. The thalamus and basal ganglia are the major relay stations in the brain⁴⁶ and are central to cortical connectivity and effective neural functioning. Reductions in thalamic and basal ganglia volumes have previously been associated with more impairments in functioning in preterm populations.^47–49 We also noted that greater average daily breast milk intake was associated with larger hippocampus volume at term equivalent. The hippocampus is important for memory and learning⁵⁰ and we have show previously in this cohort that larger hippocampal volume is associated with better working memory,⁵¹ with similar findings in another study of preterm adolescents.⁵² Possibly related to our current finding of larger hippocampal volume associated with breast milk, we also noted better working memory in association with greater breast milk intake. Overall, these findings regarding volume of the deep nuclear gray matter and hippocampus may offer clues regarding mechanisms by which breast milk feeding influences later neurodevelopmental outcomes.

The strengths of our study include the high follow-up rate to 7 years, detailed measures of neurodevelopment, and brain MRIs performed at two time points. This study focused on regional volumetric outcome measures from structural MRI. Future analysis of data from our cohort in relation to breast milk intake could include diffusion measures that reflect white matter microstructural organization.¹⁶ We could not assess brain growth during the neonatal hospitalization (e.g. change in size from birth to term), which would be of interest given concerns that even fortified breast milk may not provide adequate nutrition for very preterm infants.^{9, 10, 42} We focused on breast milk intake in the first 28 days of life, with the advantage that there was very little attrition due to early transfer or discharge that could bias results. In a subset of our participants, intake during the first 28 days was highly correlated with intake later in the hospitalization; it is likely that continued breast milk intake beyond 28 days contributed to outcomes. A limitation is that we did not collect information about breast milk intake or breastfeeding after neonatal discharge. Additionally, like any observational study, ours is subject to residual confounding. It is notable that many of our estimates were unaffected by adjustment for social and other risks, however we lacked data on maternal IQ or parenting style and therefore could not adjust for these potential confounders.

We found that greater breast milk feeding in the first 28 days of life was associated with larger deep nuclear gray matter and hippocampal volume at term equivalent age, and with higher IQ, academic achievement, working memory, and motor scores at 7 years of age in very preterm infants. These results provide support for national⁵³ and international⁵⁴ recommendations to provide breast milk as the primary diet for preterm infants.

Abbreviations

CELF-IV

Clinical Evaluation of Language Fundamentals

CRIB

Clinical Risk Index for Babies

MABC2

Movement Assessment Battery for Children, MABC2

MDI

Mental development index

MRI

Magnetic resonance imaging

PDI

Psychomotor development index

TEA-Ch

Test of Every Day Attention for Children, TEA-Ch

TVPS-3

Test of Visual Perceptual Skills

WASI

Wechsler Abbreviated Scale of Intelligence

WRAT4

Wide Range Achievement Test

WMTBC

Working Memory Test Battery for Children