This longitudinal study will examine the associations of the steroid hormones, testosterone and cortisol, levels with infant health, mother-infant interactions, and infant cognitive/motor/language development ('infant development') in very low birthweight (VLBW, BW < 1,500 g) preterm (gestational age < 32 weeks gestation) infants after adjusting for maternal physical and mental health state, infant socioemotional and behavioral development, and characteristics of infants and mothers. Concurrent and repeated measurement of testosterone and cortisol levels both in infants and mothers will be conducted through infancy and early childhood (at birth, 40 weeks postmenstrual age, 12 and 24 months corrected age).