The relationship of maternal weight status to birth weight was evaluated retrospectively for the first and second pregnancies of 72 younger (age 12-15 years at first conception) and 80 older (age 16-19 years at first conception) low-income adolescents (76% black, 24% white). Mean birth weight increased during the second pregnancies of both groups (277 g and 132 g, respectively). Multiple regression analysis (controlling for potentially confounding variables) indicated a positive relationship between second and third trimester rate of maternal weight gain (kg/week) and birth weight for younger adolescents during their second pregnancy (p = 0.014), and for older adolescents during their first pregnancy (p = 0.047). Mean birth weight increased with each increase in maternal weight-for-height (W/H) category near term from the lowest (< 100% of standard) to the highest (> or = 140% of standard), for both age groups during both pregnancies. Multiple regression analysis indicated that among older adolescents birth weight increased 4.2 +/- 2.0 g (X +/- SE) for each 1% increase in maternal W/H near term in their first pregnancy (p = 0.038) and 7.1 +/- 1.8 g for each 1% increase in maternal W/H near term in their second pregnancy (p = 0.0003). Among younger adolescents these relationships, while in the same direction, were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)