Fetal and neonatal prostacyclin and thromboxane in relation to mode of delivery.

To study whether prostacyclin and thromboxane A2 might play a role in neonatal adaption pieces of the umbilical arteries of infants born vaginally (n = 18) or by elective caesarean section (n = 11) were superfused in vitro and the release of 6-keto-PGF1a (hydration product of prostacyclin) and thromboxane B2 (metabolite of thromboxane A2) measured by radioimmunoassay. In addition, the capacity of fetal platelets to produce thromboxane A2 and the neonatal urinary concentrations of 6-keto-PGF1a were measured. Infants born by caesarean section had lower diastolic blood pressure, higher heart rate, and smaller differences between rectal and skin temperature compared with infants born vaginally during the first two hours of life. The only difference encountered in the prostanoids between the groups was reduced urinary excretion of 6-keto-PGF1a in infants born by caesarean section, whose release of 6-keto-PGF1a by the umbilical artery was positively correlated with heart rate, respiration frequency, and dermal temperature. Thus prostacyclin may be a regulatory determinant, particularly in infants born by caesarean section.