Acid-Base Significance of Meconium Discovered Prior to Labor

Although the significance of meconium in the amniotic fluid diagnosed during labor remains problematic, there is little information regarding the significance of meconium discovered prior to labor. The present study consisted of 40 term pregnancies with meconium found at amniocentesis for lung maturity (n = 7) or elective cesarean section (n = 33) and 40 uncomplicated, control pregnancies with clear amniotic fluid at elective cesarean section. The mean umbilical artery (UA) blood pH was 7.26 in the meconium group and 7.28 in the control group. Overall, the frequency of fetal acidemia (UA pH <7.20) was 15% (6 of 40) of the infants in the meconium group versus 8% (3 of 40) in the control group (p = 0.24). All nine of these infants had a respiratory acidosis defined as a UA blood pH less than 7.20 with normal bicarbonate and elevated carbon dioxide pressure. Importantly, none of the neonates had metabolic acidemia and all had uncomplicated hospital courses. All of the pregnancies reported were promptly delivered because of meconium and we therefore cannot recommend nonintervention when meconium is diagnosed in the antepartum period. Meconium discovered prior to labor is not necessarily a marker of immediate or chronic fetal compromise.