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The impact of fetal size and length of gestation on 6‐sulphatoxymelatonin excretion in adult life

Recent studies have shown that intrauterine growth retardation or fetal distress in human infants is associated with a pronounced reduction in melatonin secretion during the first 3 months of life. It is not known whether these associations persist beyond infancy. We have therefore examined the relationship between birthsize and melatonin secretion in 159 men and women aged 20, born in Adelaide, South Australia. Melatonin secretion was estimated by analysing the overnight urinary excretion of 6‐sulphatoxymelatonin. The overnight excretion ranged from 1.7 to 128.9 nmoles/subject, was higher in women than in men (46.5 vs 34.1 nmoles, P=0.003) and was significantly negatively correlated with the body mass index (P=0.006). Excretion correlated with both birthweight and ponderal index at birth (P=0.04 and P=0.01 respectively after adjustment for gestational age) and also fell with increased duration of gestation (P=0.007). The effects of adult body mass index added to that of low birthweight in predicting 6‐sulphatoxymelatonin excretion. These data suggest that urinary 6‐sulphatoxymelatonin excretion was impaired in adults who were growth restricted prenatally or were delivered after 40 weeks gestation.