BLOOD-PRESSURE IN PROSPECTIVE POPULATION-BASED COHORT OF NEWBORN AND INFANT TWINS

Objective-To describe blood pressure in twins during infancy. Design-P rospective study of cohort of twins. Setting-Teaching hospital in Flor ida. Subjects-166 viable twin pairs born between July 1976 and Decembe r 1989. Main outcome measures-Blood pressure and body weight at birth, at 14 days, and at 1, 3, 6, 9, and 12 months. Results-Both systolic a nd diastolic pressure correlated with body weight throughout infancy ( at birth r = 0.41, P < 0.001 and r = 0.42, P < 0.001 respectively; at 1 year r=0.23, P < 0.001 and r=0.26, P < 0.001 respectively). In infan ts weighing < 1500 g at birth mean blood pressure rose from about 45/2 5 mm Hg to 101/55 mm Hg from birth to the age of 1 year, while in infa nts weighing > 3000 g at birth it rose from 63/39 mm Hg to 100/61 mm H g; corresponding mean body weights at 1 year were 7.86 kg and 9.58 kg. Differences in birth weight within pairs of monozygotic twins were ne gatively correlated with such differences in systolic blood pressure a t 1 year (r = -0.37, P < 0.01). Conclusions-Blood pressure and body we ights in twins showed strongly positive but generally declining correl ations throughout infancy. Twins Of lower birth weight showed a more r apid rate of rise in blood pressure during infancy. At 1 year the catc h up in blood pressure exceeded that in body weight. Greater differenc es in birth weights between monozygotic twins were associated with sma ller differences in systolic blood pressure at 1 year, suggesting that intrauterine environmental factors related to birth weight are import ant in determining blood pressure in infancy.