Birthsize, gestational age and adrenal function in adult life: studies of dexamethasone suppression and ACTH1-24 stimulation

OBJECTIVE: Several studies show that low birthweight is associated with long-term alterations in the function of the hypothalamic-pituitary-adrenal axis (HPAA). We recently reported that the relationship between birthweight and fasting serum cortisol concentrations differed according to the gestational age of the babies, suggesting that both hypercortisolism and hypocortisolism could be a consequence of impaired fetal growth. We have now extended these findings by examining the relationship between birthweight, gestational age and tests of adrenal suppression and stimulation. DESIGN: Prospective birth cohort study. SUBJECTS AND METHODS: We studied 165 women (mean age 71.3 Years) born at term in Helsinki, Finland, between 1924 and 1933, whose body size and gestational age at birth were recorded. These women underwent an overnight 0.25 mg dexamethasone suppression test followed by a 1 microg ACTH(1-24) stimulation test. RESULTS: In all women combined, low birthweight was associated with lower total (P=0.03) and free (P=0.02) cortisol concentrations following dexamethasone. However, these relationships were dependent on gestational age at birth, interactions between the effects of birth size and gestational age on dexamethasone responsiveness being statistically significant. To demonstrate these interactions, we divided the study population into two groups according to gestational age. In subjects born at 40 weeks of gestation or more, low birthweight was strongly associated with enhanced dexamethasone suppression (P=0.003 for total and P=0.0004 for free cortisol), while in subjects born before 40 weeks of gestation there was no association. There was, however, no correlation between birth size and the adrenal response to ACTH(1-24). CONCLUSIONS: These findings reinforce our suggestions that events during prenatal life may lead to both up-regulation and down-regulation of the HPAA.     

Type 2 (non-insulin-dependent) diabetes mellitus,hypertension and hyperlipidaemia (syndrome X): relation to reduced fetal growth

Summary Two follow-up studies were carried out to determine whether lower birthweight is related to the occurrence of syndrome X — Type 2 (non-insulin-dependent) diabetes mellitus, hypertension and hyperlipidaemia. The first study included 407 men born in Hertfordshire, England between 1920 and 1930 whose weights at birth and at 1 year of age had been recorded by health visitors. The second study included 266 men and women born in Preston, UK, between 1935 and 1943 whose size at birth had been measured in detail. The prevalence of syndrome X fell progressively in both men and women, from those who had the lowest to those who had the highest birthweights. Of 64-year-old men whose birthweights were 2.95 kg (6.5 pounds) or less, 22% had syndrome X. Their risk of developing syndrome X was more than 10 times greater than that of men whose birthweights were more than 4.31 kg (9.5 pounds). The association between syndrome X and low birthweight was independent of duration of gestation and of possible confounding variables including cigarette smoking, alcohol consumption and social class currently or at birth. In addition to low birthweight, subjects with syndrome X had small head circumference and low ponderal index at birth, and low weight and below-average dental eruption at 1 year of age. It is concluded that Type 2 diabetes and hypertension have a common origin in sub-optimal development in utero, and that syndrome X should perhaps be re-named the small-baby syndrome.     

Age, period, and cohort models. Non-overlapping cohorts don't resolve the identification problem

Age, period, and cohort models have generally been applied to rates from tabulated national statistics, and it is known that such models suffer from an identification problem. When individual records, including date of birth, are available, however, a unique solution has been proposed which uses non-overlapping cohorts. We have shown that the identification problem exists in continuous time, so that even perfect information on the three variables will fail to resolve it. It is important to recognize clearly the assumptions that are implicit in the non-overlapping cohort formulation of the age-period-cohort model. The value of the solution proposed depends critically on their appropriateness or otherwise. It should always be remembered that the assumptions determine much of the final solution, including the apportionment of trend to the different components, age, period, or cohort.