Meconium Aspiration is defined as.....Intrauterine passage of meconium into the amniotic fluid related to intrauterine stress
Passage of meconium can occur at any time during the antenatal or intrapartal (labor and delivery) periods
It's estimated between 7%-22% of term infants pass meconium at the time of delivery
This estimation climbs to 40% in post-term deliveries
The amount of meconium passed in utero affects the appearance and viscosity of the amniotic fluid
This impacts the outcome for the infant
Chronic over-time exposure to meconium, as opposed to an acute single-time exposure, may result in more severe outcomes for the infant
Diagnosis of MAS should be made only after all other reasons for respiratory compromise have been ruled out
Meconium aspiration in utero continues to represent a leading cause of neonatal morbidity and mortality
Who's At Risk?
MAS is seen most frequently in the term, post-term and growth retarded infant
Usually affects the fetus who is > 37 weeks' gestation
Greater than 98% of these fetuses have been noted to have meconium-stained fluid
Incidence of meconium-stained amniotic fluid increases steadily with increasing gestational age
Common occurrence in post-term fetus
If infant is a breech delivery, may be ignored and accepted as normal event--but should not be dismissed
Unusual in < 36 weeks' gestation
Rare occurrence in the preterm fetus
Appearance in the premature may indicate severe disease since this is not a normal event
Meconium may also be a marker of chronic intra-uterine hypoxia
"Old" yellow meconium indicates prolonged fetal hypoxia and is an ominous sign
Intra-uterine growth retarded (IUGR) infants
Whatever the underlying cause of the IUGR may contribute to the occurrence of MAS
Intrapartal fetal distress
Some early studies supported a correlation between abnormal fetal heart rate patterns in the presence of meconium stained fluid as increasing perinatal morbidity and mortality
These events then contribute to low 1-minute and 5-minute Apgar scores
Additional studies have not produced definitive support but inquiry continues
