['Elevated maternal psychosocial stress during pregnancy and accompanying changes in stress hormones may contribute to risk of adverse birth outcomes such as low birth weight and preterm birth. Relatedly, research on fetal programming demonstrates intriguing associations between maternal stress processes during pregnancy and outcomes in offspring that extend into adulthood. The purpose of this study was to test whether hypothalamic-pituitary-adrenal (HPA) patterns in mothers during the period between 2 pregnancies (i.e., the interpregnancy interval) and during the subsequent pregnancy predict infant birth weight, a key birth outcome.', 'This study sampled salivary cortisol before and during pregnancy in a diverse community sample of 142 women enrolled in the Community Child Health Network study.', 'Using multilevel modeling, we found that flatter diurnal cortisol slopes in mothers during the interval between one birth and a subsequent pregnancy predicted lower infant birth weight of the subsequent child. This interpregnancy cortisol pattern in mothers also correlated with significantly shorter interpregnancy intervals, such that women with flatter cortisol slopes had more closely spaced pregnancies. After adding demographic covariates of household income, cohabitation with partner, and maternal race to the model, these results were unchanged. For participants who provided both interpregnancy and pregnancy cortisol data (n = 73), we found that interpregnancy cortisol slopes predicted infant birth weight independent of pregnancy cortisol slopes.'] Do diurnal salivary cortisol patterns prior to pregnancy predict infant birth weight?