Aim: To compare ambulatory blood pressure monitoring (ABPM) in twin children to a published singleton population, and to examine the influence of birthweight and fasting plasma cortisol on blood pressure.
Design: A cross-sectional study of monozygotic and dizygotic twins compared with a similar previously published normative control population.
Methods: Forty-four healthy prepubertal twin children aged 4-11 years (20 monozygotic, 22 male) were studied. All subjects had 24-h ABPM and a fasting early morning plasma cortisol.
Results: Twins had higher 24-h systolic blood pressure (BP) compared with controls with similar daytime and elevated night-time systolic BP (P > 0.3 and P < 0.01, respectively). Twins had reduced systolic and diastolic nocturnal BP dipping compared with controls (P < 0.0001 for both), and 61% of twins exhibited a < 10% fall in nocturnal BP. In the twin cohort there was no association between birth weight and daytime systolic BP (P = 0.6), nor any other ABPM parameter. There was no difference in BP parameters between dizygotic and monozygotic twins, and no difference between the lighter and heavier birthweight twins for any ABPM parameter. Fasting plasma cortisol was not associated with either birthweight (P = 0.2) or daytime systolic BP (P = 0.4).
Conclusions: Healthy prepubertal twins have increased nocturnal BP and reduced nocturnal BP dipping independent of zygosity or birthweight. These abnormalities may be a risk factor for the later development of hypertension in twins. As these BP abnormalities are not associated with twin birth weight, the twin model may not be appropriate in investigating the fetal origins of disease in later adult life.