Effect of fat and fat-free mass deposition during pregnancy on birth weight Jose Villar, MD,.. b Mary Cogswell, DrPH,c Edgard Kestler, MD," Patricia Castillo, RN," Romeo Menendez, MD," and John T. Repke, MDd Baltimore and Bethesda, Maryland, and Guatemala City, Guatemala OBJECTIVES: The purposes of our study were to describe the patterns and location of fat and fat-free mass deposition during pregnancy and to evaluate their effects on fetal growth. STUDY DESIGN: Our study is a prospective follow-up of 105 healthy pregnant women who were delivered of term infants. Body composition was evaluated eight times during gestation with anthropometric measures and bioimpedance techniques. Body fat and fat-free mass were calculated with equations specifically developed for this population. RESULTS: Total weight gain was 10.0 ± 3.5 kg; net weight gain was 3.7 ± 0.31 kg; birth weight was 3211 ± 467 gm (values are mean ± SEM). In these women fat was deposited mostly in the thigh and subscapular region for a total of 6.23 ± 0.19 kg at term. The period of pregnancy of the largest maternal fat deposition per week is between the twentieth and thirtieth weeks. After adjusting by prepregnancy weight, birth weight is associated with maternal changes in thigh skin folds and fat gain before the thirtieth week of gestation. Infants born to mothers with low fat gain before the thirtieth week were 204 gm lighter than infants born to mothers with fat gain ~25th percentile of this population. CONCLUSION: Maternal nutritional status at the beginning of gestation and the rate of fat gain early in pregnancy are the two nutritional indicators most strongly associated with fetal growth in this population. (AM J OBSTET GVNECOL 1992;167:1344-52.)

Key words: Birth weight, fat deposition, body composition changes during pregnancy

Maternal nutritional status as evaluated by prepregnancy weight, height, or weight gain during gestation has repeatedly been demonstrated to be associated with birth weight. 1 Furthermore, increased caloric intake with a presumably improved nutritional status also appears to influence birth weight. 2.3 Although the overall effect of weight gain during pregnancy has been established, its components (fat vs fat-free mass), the timing of tissue deposition and the independent effect of these factors on birth weight have yet to be completely described. Two early reports preFrom the Division of Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health'; the Perinatal Research Program, Guatemalan Social Security Obstetrics and Gynecological Hospital (IGSS)'; the Department of International Health, The Johns Hopkins University School of Hygiene and Public Health'; and the Department of Gynecology and Obstetrics, The Johns Hopkins HospitaU Supported by the Research Grant Program, Board of Sciences and Technology for International Development, National Academy of Sciences, grant No. REA GT 4-84-2. Presented in part at the Thirty-sixth Annual Meeting of the Society for Gynecologic Investigation, San Diego, California, March 15-18,

1989.

Received for publication November 11, 1991; revised March 25, 1992; accepted April 8, 1992. Reprint requests: J. Villar, MD, Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, 1211 Geneva 27, Switzerland. 611 138549

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sented the patterns of fat-fold changes in a wellnourished' and an undernourished population." These two reports and body composition changes during pregnancy estimated with the factorial method 6 have been the basis for the study of these issues up to recent years. The introduction of nonradioactive methods of body composition estimation 7 has created new possibilities for a more adequate evaluation of body composition and energy balance during pregnancy in populations and their relationship with birth weight. 8.9 Our report describes the patterns and location of fat and fat-free mass deposition during pregnancy and prospectively evaluates the effects of these patterns and components of tissue accretion on birth weight.

Material and methods We report a prospective follow-up study conducted within the Perinatal Research Program of the Guatemalan Social Security Obstetrics and Gynaecological Hospital and the Institute of Nutrition of Central America and Panama. Between October 1985 and December 1986, 123 pregnant women enrolled for prenatal care in the perinatal nutrition unit before the seventeenth week of gestation. A detailed description of this population has been published elsewhere. 10. 11 In brief, these women were employed or married to employed men covered by the

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Social Security Institute, with the majority belonging to the low-to-middle urban class. All participants were clinically healthy, with known date of last menstrual period and without clinical evidence of malnutrition, history of pregnancy complications, or abnormal baseline laboratory test. None had abnormal edema. From the original group of 123 enrolled patients 18 are excluded from our report because they either had their first body composition measure after 16 weeks (n = 9) or they were delivered at

Effect of fat and fat-free mass deposition during pregnancy on birth weight.

The purposes of our study were to describe the patterns and location of fat and fat-free mass deposition during pregnancy and to evaluate their effect...
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