Vasoconstrictive activity of meconium stained amniotic fluid in the human placental vasculature

Objective: The purpose of this study was to study was to determine the effe ct of meconium stained amniotic fluid on the vasculature of isolated perfus ed human placental cotyledon. Study Design: Isolated placental cotyledons w ere dually perfused. Fetal perfusion pressure was used as an index of vascu lar resistance. Meconium stained amniotic fluid (MSAF) was collected from p atients after artificial rupture of membranes in term gestation. A dilution of meconium (1:2; 1:4; 1:8; 1:16) was performed. Optical density (OD) of M SAF varied between 0 and 35.0 units/g as determined by spectrophotometry. B olus injections of 1.0 mi of MSAF at different concentrations were injected into the fetal circulation. Heated and dialyzed MSAF after adequate diluti on and evaluation of optical density were injected into fetal circulation i n separate experiments. Results: Analysis of variance (ANOVA) and paired t- test were used for statistical analysis. Bolus injections of MSAF into the fetal circulation resulted in a concentration-dependent increase in perfusi on pressure. MSAF with the highest OD resulted in a greater change in perfu sion pressure as compared to more dilute MSAF (P=0.0001). After high OD amn iotic fluid injections the provoked contractions lasted longer compared to dilute MSAF (P=0.006). MSAF after dialyzation did not exhibit any vasoconst rictive effect. Conclusion: Meconium is a vasoconstrictive agent in the fet al-placental vasculature and has a concentration dependent effect. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.