While we do not fully understand why some babies pass meconium stool into the amniotic fluid, doctors believe that in some cases (but not always) it may be related to fetal stress, which may be linked to infections, decreased oxygen in utero, or a long or difficult labor. When the meconium mixes into the amniotic fluid, it can be swallowed and breathed into the fetus’s airways, and then, when the baby takes its first breaths outside the womb, these particles can be aspirated deep into the lungs.
Risk factors include:
- Aging placenta (if the pregnancy goes too far past its due date; in fact, premature babies have less of a chance of having meconium aspiration syndrome)
- Difficult labor
- Gestational diabetes, maternal high blood pressure, or a mother who smokes cigarettes heavily or has chronic respiratory or cardiovascular disease
- Umbilical cord complications
- Poor growth of the baby while in the uterus
- Chorioamnionitis, infection during labor