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Milk Intake in Pregnancy Linked to Larger Infant Size at Birth

Authors: News Author: Laurie Barclay, MD CME Author: Penny Murata, MDFaculty and Disclosures


October 11, 2007 — Intake of milk in pregnancy was associated with higher birth weight for gestational age, lower risk for small for gestational age (SGA), and higher risk for large for gestational age (LGA), according to the results of a prospective cohort study published in the October issue of the American Journal of Clinical Nutrition.

"Cow milk contains many potentially growth-promoting factors," write Sjurdur F. Olsen, from the Institute of Public Health, University of Aarhus in Denmark, and colleagues from the NUTRIX Consortium. "There is a lack of large prospective studies with a sizeable group of women with zero or low milk consumption. We therefore examined in detail, in a large prospective Danish pregnancy cohort, the relations of milk intake and milk constituents with measures reflecting intrauterine growth."

From 1996 to 2002, the Danish National Birth Cohort collected questionnaire data from 50,117 mother-infant pairs on midpregnancy diets, determined covariates through telephone interviews, and evaluated birth outcomes through registry linkages. Results were adjusted for the mother's parity, age, height, body mass index (BMI) before pregnancy, gestational weight gain, smoking status, and total energy intake, as well as the father's height and the family's socioeconomic status.

Mean intake of milk was 3.1 ± 2.0 glasses per day. Intake of milk was inversely associated with the risk of SGA birth and directly associated with both LGA birth and mean birth weight (P for trend < .001).

Comparing women drinking 6 glasses or more per day with those drinking 0 glasses per day, the odds ratio (OR) for SGA birth was 0.51 (95% confidence interval [CI], 0.39 - 0.65), and 1.59 (95% CI, 1.16 - 2.16) for LGA birth. The increment in mean birth weight was 108 g (95% CI, 74 - 143 g). There were also graded relationships for abdominal circumference (0.52 cm; 95% CI, 0.35 - 0.69 cm), placental weight (26 g; 95% CI, 15 - 38 g), birth length (increment, 0.31 cm; 95% CI,
0.15 - 0.46 cm), and head circumference (0.13 cm; 95% CI, 0.04 - 0.25 cm; P < .001 for all).

Birth weight was associated with protein intake derived from milk but not with fat intake.

"Milk intake in pregnancy was associated with higher birth weight for gestational age, lower risk of SGA, and higher risk of LGA," the study authors write. "The data presented herein lead us to hypothesize that water-soluble substances in milk increase fetal growth. The implications that such increases in growth could have for newborn health depend on the underlying factors and mechanisms."

Limitations of the study include measurement of milk intake during a narrow time window of pregnancy, nonparticipation of women eligible for recruitment, attrition among the women recruited, and restriction of analyses to include only singleton infants born at term.

"Identifying means to increase fetal growth rate may lead to new measures for the prevention of neonatal mortality and morbidity and possibly of adult cardiovascular diseases and type 2 diabetes associated with low birth weight," the study authors conclude. "However, milk intake was associated not only with a decreased risk of SGA but also with an increased risk of LGA, and a rapid early growth rate may be a risk factor for obesity, cancer of the breast, and reduced longevity. More research is needed to identify the causative factors in cow milk and to examine whether the possible growth-stimulating effect of cow milk is beneficial or deleterious to the health of the fetus in the short term as well."

The March of Dimes Birth Defects Foundation, Danish National Research Foundation, Pharmacy Foundation, Egmont Foundation, Augustinus Foundation, Health Foundation, European Union, Danish Medical Research Foundation, and Heart Foundation supported this study. The study authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2007;86:1104-1110.

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