Sex-specific differences in peripheral microvascular blood flow in preterm infants.

Microvascular blood flow is related to physiologic instability in newborn preterm infants. We investigated sex-specific differences in basal microvascular blood flow and the ability of the microvasculature to respond to vasoactive stimuli following preterm birth. Ninety-six infants in two gestational age groups (24-28 and 29-36 wk) were studied on days 1-5 of life. Laser Doppler flowmetry was used to measure baseline microvascular blood flow and vasodilatation in response to acetylcholine and local warming. A significant interaction of gestational age and sex was observed for baseline flow at 24 h of age. In the 24-28 wk group, male infants had higher baseline flow than females. Male, but not female, infants born at 24-28 wk exhibited a significant relationship between baseline flow and vasodilatory response to acetylcholine at 24 h of age. By 120 h of age, both sexes exhibited similar responses. Infants born at 24-28 wk exhibited greater vasodilatation in response to local warming than those born at 29-36 wk at 24, 72, and 120 h of age. Sex-specific differences in microvascular blood flow and vasodilatory capacity in the immediate newborn period may affect the transitional circulation, contributing to excess of morbidity and mortality in preterm males.