infants thinner at birth exhibit smaller kidneys for their size in late gestation in a sample of...

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Infants Thinner at Birth Exhibit Smaller Kidneys for Their Size in Late Gestation in a Sample of Fetuses With Appropriate Growth MICHELLE LAMPL, 1 * CHRISTOPHER W. KUZAWA, 1 AND PHILIPPE JEANTY 2 1 Department of Anthropology, Emory University, Atlanta, Georgia 30322 2 WomenÕs Health Alliance, Nashville, Tennessee 37203-2131 ABSTRACT Fetal ultrasound measurements were employed to investigate the relationship be- tween weight and ponderal index at birth and kidney size during the second (23 weeks) and third (32 weeks) trimesters of pregnancy in a sample of 25 normally growing fetuses. Kidney volume and kidney volume / fetal weight ratio at 32 weeks are significantly and positively related to both weight and ponderal index at birth, controlling for sex, gestational age at birth, and day of ultrasound measurement. A second-degree polynomial relationship approximates the predictability of kidney volume fetal weight ratio at 23 weeks to that at 32 weeks, demonstrating shifting growth rates in fetal organ and body growth relationships during midgestation. Sex and parental size are suggested as contributing to these patterns. Females have a surge in renal growth between 23 and 32 weeks to catch up to earlier growing males, and maternal weight significantly predicts incremental growth in kidney volume and the kidney volume / fetal weight ratio at 32 weeks of gestation. The observation that fetuses relatively thin at birth have relatively smaller kidneys for their size in late gestation suggests that the influence of maternal weight on birth outcome may act through organ growth. Am. J. Hum. Biol. 14:398±406, 2002. Ó 2002 Wiley-Liss, Inc. Birthweight is ubiquitously employed as a marker of prenatal growth in numerous studies positing adult morbidity sequelae of fetal development. Whether birthweight is a good proxy for fetal growth is debatable in this context. A question that remains to be answered is the following: What is it about size at birth that predicts later health in some individuals? Published epidemiologi- cal observations suggest that underlying relationships between organ growth and birth size may be important. Research tracking traits such as blood pressure across developmental stages has reported inverse dose±response relation- ships across the entire range of birth- weights. Observations that individuals of average birthweight have higher blood pressure than individuals of above-average birthweight (Barker et al., 1989, 1993; Os- mond et al., 1993; Valdez et al., 1994) have provoked much debate regarding underly- ing mechanisms (Law and Shiell, 1996). While subsequent research has often fo- cused on the study of low birthweight neonates and employed nutritional insuffi- ciency as the fetal growth model of causa- tion, an unanswered question is why adult disease risk has been observed to increase continuously and in a dose±response fash- ion as fetal size or the ponderal index at birth declines? Organ-level studies may provide addi- tional information. The present study em- ploys fetal ultrasound measurements to investigate normal variation in birthweight with respect to kidney growth, an organ currently central to hypotheses linking the fetal environment with postnatal blood pressure regulation (Ingelfinger and Woods, 1999). A relationship between fetal kidney growth and adult blood pressure levels was first hypothesized over a decade ago, when Brenner et al. (1988) posited a direct rela- tionship between kidney size and functional outcome. Observations of smaller kidneys in populations prone to hypertension provided early support and animal models extended these observations (Fassi et al., 1998; Langley-Evans et al., 1999; Merlet-Beni- chou et al., 1994). Controversy presently surrounds these propositions in humans (Manalich et al., 2000; Haycock 2001; Jones et al., 2001). This investigation used ultrasonographic data to investigate the relationship between birth outcome in terms of weight and the *Correspondence to: M. Lampl, Department of Anthropology, Emory University, Atlanta, GA. E-mail: [email protected] Received 19 June 2001; Revision received 3 December 2001; Accepted 4 December 2001 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ajhb.10050 AMERICAN JOURNAL OF HUMAN BIOLOGY 14:398±406 (2002) ã 2002 Wiley-Liss, Inc.

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Page 1: Infants thinner at birth exhibit smaller kidneys for their size in late gestation in a sample of fetuses with appropriate growth

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Page 2: Infants thinner at birth exhibit smaller kidneys for their size in late gestation in a sample of fetuses with appropriate growth

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