In vitro model of human umbilical venous perfusion to study the effects of meconium staining of the umbilical cord.

Because meconium diffuses into placental and umbilical cord tissue, its bioactive components are potentially capable of entering the fetal circulation. Meconium diluted in Krebs solution produces vasoconstriction in human umbilical vein segments that are suspended in a milieu similar to that of the amniotic cavity. Based on published observations, we wanted to determine if very diluted meconium could induce vasospasm in intact umbilical cords. Human umbilical cords were obtained from full-term deliveries, cut into 2 equal segments, cannulated, and perfused continuously as test and control cords. The study included four parts: (1) intraluminal meconium (n = 6; 0.01-1% solution); (2) 4-hour exposure to 10% meconium-stained amniotic fluid of intact umbilical cords (n = 8); (3) 4-hour exposure to a 10% meconium-stained amniotic fluid of umbilical cords denuded of their epithelial layer (n = 5); (4) 24-hour exposure to a 10% meconium-stained amniotic fluid of intact umbilical cords (n = 9). Significant vasoconstriction of the umbilical vein occurred only with the intraluminal meconium solution exposure (p = 0.034). In this in vitro model meconium staining of the umbilical cord was not associated with vasoconstriction of the umbilical vein.