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 effect of meconium stained amniotic fluid on the vasculature of isolated perfused human placental cotyledon. Study Design: Isolated placental cotyledons were dually perfused. Fetal perfusion pressure was used as an index of vascular resistance. Meconium stained amniotic fluid (MSAF) was collected from patients 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 MSAF varied between 0 and 35.0 units/g as determined by spectrophotometry. Bolus injections of 1.0 ml of MSAF at different concentrations were injected into the fetal circulation. Heated and dialyzed MSAF after adequate dilution and evaluation of optical density were injected into fetal circulation in 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 perfusion pressure. MSAF with the highest OD resulted in a greater change in perfusion pressure as compared to more dilute MSAF (P=0.0001). After high OD amniotic fluid injections the provoked contractions lasted longer compared to dilute MSAF (P=0.006). MSAF after dialyzation did not exhibit any vasoconstrictive effect. Conclusion: Meconium is a vasoconstrictive agent in the fetal-placental vasculature and has a concentration dependent effect. Copyright (C) 1999 Elsevier Science Ireland Ltd.