Eleven thousand eighty-two term, singleton pregnancies were analyzed for clues to how different levels of maternal blood pressure affect fetal growth. Birth weights progressively increased with increasing pressures until the hypertensive range was reached when maternal edema and proteinuria were absent. Pressure-associated increases in fetal growth were even more rapid when mothers were edematous, and slower when 2+ or greater proteinuria was present. Birth weights leveled off or decreased when pressures reached the hypertensive range. The pressure threshold at which growth slowed increased from diastolic 75 mm Hg in the lowest maternal pregnancy weight gain category to nearly 100 mm Hg in the highest weight gain category. Decreases in birth weight associated with hypertension were most severe when mothers were thin and had low pregnancy weight gains. Diuretics reduced birth weights in low maternal weight gain pregnancies but not in high weight gain ones.