Is umbilical cord prolapse secondary to fetal acidemia?

Aims The objective of the present study was to examine whether umbilical cord vessels are less responsive to vasoconstricting agents in the presence of acidosis. We speculated that some of the cases of cord prolapse during labor might be related to a lower 'baseline' tone of the umbilical vessels secondary to pre-existing fetal acidosis. Materials and methods Umbilical cord segments obtained from uncomplicated pregnancies at term were incubated under in vitro conditions. Maximal responses to 120 mmol/l potassium HEPES and dose response to 5-hydroxytryptamine (5-HT) were measured under different pHs (7.4, 7.2, 7.0, 6.8) of the HEPES solution. Results There was a marked decrease in maximum response to 5-HT and a decrease in the Hill coefficient in response to 5-HT as the pH in the bath decreased. Conclusion The in vitro response of umbilical cord vessels to a vasoconstrictor decreased as pH decreased. We speculate that changes in the pH, within the range observed in fetal acidosis, could alter the firmness of the umbilical cord. We propose that some fetuses could experience cord prolapse secondary to a pre-existing undiagnosed fetal acidemia.