Scalp hair samples were studied from 10 term infants of normal weight for dates, 10 infants born very early of normal weight for dates and 10 infants born near term who were small-for-dates. The samples were examined morphologically and the diameters measured precisely using a scanning electron microscope. The control term-normal weight for dates infants had hairs which tapered gradually to the tip. Infants born very early had narrower hairs: these could be superimposed on the distal segments of the term infants hairs. Small-for-dates infants had hairs which where shorter and of narrower diameter for gestational age than the equivalent hair segments from normally grown infants, implying growth constraint from about 20 weeks of gestation. Amino acid analysis of the hairs from the three groups of infants showed no differences in concentration. These data suggest that no specific disturbance of any one or any groups of amino acids is the growth-limiting factor on the fetus as a whole in intra-uterine growth retardation.

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