Blood pressure during the first two years of life.

Blood pressure (BP) was measured on the third postnatal day in 392 healthy, full-term, appropriate weight infants, and again in 318 infants at six months, in 277 infants at 15 months, and in 232 infants at 24 months of age. Differences in average BP between white infants and black infants were small; BP did not vary significantly as a function of socioeconomic class or sex. BP, measured during sleep, had increased from birth to six months of age, but showed no change from six to 15 months, a period of rapid growth, during which average weight increased 37% and average height increased 16%. BP continued to show to change from 15 to 24 months, when waking BP measurements at 24 months were adjusted for sleep-waking differences in BP. Cross-sectional and analyses revealed only modest weight-BP relationships at 15 and 24 months. Five per cent of the infants exhibited systolic BPs which remained above the 80th percentile at six, 15, and 24 months of age. This was six times the number expected by chance if BP was assumed to be uncorrelated from measurement to measurement. This group of infants showed physical maturation, measured by weight change, which was almost identical with that of the total cohort.