Meconium-Associated Umbilical Vascular Myonecrosis: Correlations with Adverse Outcome and Placental Pathology.

Intrauterine passage of meconium is common, occurring in approximately 10-15% of term births. Uncommonly, long-standing meconium exposure is associated with umbilical vascular myonecrosis, but few studies have evaluated specific clinical and pathologic features. This is a retrospective study of 481 term placentas: 139 with meconium-associated myonecrosis, 139 with meconium in fetal membranes, only 62 with meconium in the cord without myonecrosis, and 139 controls without meconium. We studied clinical factors, including clinical evidence of meconium discharge, fetal distress, APGAR scores, intrauterine growth restriction (IUGR), and intrauterine fetal demise (IUFD), and histologic factors, including acute chorioamnionitis, umbilical cord complications, uteroplacental malperfusion, fetal thrombosis, chorangiosis, and fetal nucleated red blood cells. Meconium myonecrosis was significantly associated with clinical meconium, fetal distress, IUGR, IUFD, acute chorioamnionitis, cord complications, fetal thrombosis, chorangiosis, and nucleated red blood cells when compared to controls (P < 0.05). Compared to cases with meconium in the membranes only, clinical meconium, fetal distress, IUGR, chorioamnionitis, thrombosis, chorangiosis, and nucleated red blood cells remained significant. Compared to cases with meconium in the cord without myonecrosis, only chorioamnionitis retained significance. In conclusion, myonecrosis was associated with adverse clinical outcome and placental lesions associated with hypoxia. Chorioamnionitis was significantly more common in all meconium groups compared to controls. As myonecrosis is an important lesion, a clinical history of meconium should trigger a meticulous search for meconium and specifically myonecrosis.