Psychosocial stress could lead to a wide range of possible physiological reactions, due to both the total burden of stress as well as individual susceptibility. Two useful Swedish registers to investigate early life influences on stress susceptibility are the Swedish Medical Birth Register (MBR) and the Military Service Conscription Register (MSCR). In a previous study we showed a positive relation between fetal growth and psychological functioning (PF) including an assessment of stress susceptibility.¹ However, in that study we did not adjust for family social class—nor did another related study.² We have therefore now carried out such an analysis in an expanded cohort study, by adding parental educational level as a marker of family social class. The aim was to investigate independent associations between fetal growth and stress susceptibility in young men.

METHODS

We selected all Swedish men born in 1973–1979 and registered in the MBR (n = 306 497). Birth characteristics recorded in MBR were linked to data on PF in the MSCR during 1990–1997. Excluded from the conscript test are men with severe physical or mental handicap (n = 43 890). In all, 161 991 young men had complete birth data and full data on PF using the same standardised methods. The study was approved by the ethical committee, University of Lund.

Recorded MBR variables were: birth weight (g), birth length (cm), head circumference (cm), gestational age (weeks), maternal age (years), and parity (n). We used data only from …