Previously, aspiration was thought to be stimulated by fetal hypoxic episodes, and fetal heart rate tracing abnormalities were used to identiy fetuses at greatest risk during labor. Unfortunately, this was found to be an unreliable predictor (Dooley, 1985). As another potential prevention, oropharyngeal suctioning was standard care for a time. However, this was abandoned when evidence failed to support a reduction in syndrome incidence or severity (Davis, 1985; Wiswell, 1990). At the same time, reports described that pulmonary hypertension caused by aspirated meconium was characterized by abnormal arterial muscularization beginning well before birth. These findings led some to conclude that only chronically asphyxiated fetuses developed meconium aspiration syndrome (Katz, 1992). But, correlation was not found between meconium aspiration and markers of acute asphyxia-for example, umbilical artery acidosis (Bloom, 1996; Richey, 1995). Others, however, have reported that thick meconium is an independent risk factor for neonatal acidosis (Maisonneuve, 201r1).
In response to conlicting results regarding suctioning, an II-center randomized trial was designed to compare suctioning with no suctioning (Vain, 2004). There was an identical 4-percent incidence of meconium aspiration syndrome in both groups. Subsequently, a committee that represented the American Heart Association updated its guidelines (Wyckof, 2015) . Adopted by the American College of Obstetricians and Gynecologists (2017c) and the World Health Organization (2012), these recommend against routine intrapartum oro-and nasopharyngeal suctioning at delivery. For vigorous newborns, no treatment is required. For depressed newborns, management includes intervention to support ventilation and oxygenation, and intubation is used as indicated (Chap. 32, p. 609).
Intrapartum amnioinusion has been used successully in laboring women with diminished amnionic fluid volume and frequent variable fetal heart rate decelerations (Chap. 24, p. 475). Earlier, it was studied as a preventive measure in labors complicated by meconium staining. This practice failed to lower meconium aspiration syndrome rates because fetuses usually inhaled meconium before labor (Bryne, 1987; Wenstrom, 1995). To urther settle this issue, a trial was conducted with almost 2000 women at 36 weeks' gestation or later and in whom labor was complicated by thick meconium (Fraser, 2005). he perinatal death rate with and without amnioinusion was 0.05 percent in both groups. Rates of moderate or severe meconium aspiration were also not significantly diferent-4.4 percent with and 3.1 percent without amnioinusion. Finally, cesarean delivery rates were similar-32 versus 29 percent, respectively. Currently, the American College of Obstetrics and Gynecologists (2016a) does not recommend amnioinusion to reduce meconium aspiration syndrome.