Editor—To investigate the effect of antenatal steroids on thymic size, we reviewed the chest x ray pictures taken in the first 36 hours of life in two groups, each of 25 infants. The first group of infants was born in 1992–3; none of their mothers had received antenatal steroids. The second group was born in 1995–6; all of these mothers had received two doses of dexamethasone before delivery. The groups were matched for sex, birthweight (± 100 g), and gestation (±1 week). There was no significant difference in the causes of premature delivery; the most common stated cause of premature …