Final answer:
A post-term infant might pass meconium prior to birth due to fetal distress often caused by factors like maternal drug abuse, hypertension, and placental anomalies, leading to potential complications that require immediate medical attention.
Step-by-step explanation:
A post-term infant may have passed meconium prior to birth, often due to fetal distress, which is commonly associated with fetal hypoxia or oxygen deprivation. Multiple factors might contribute to this condition, including maternal drug abuse (such as tobacco or cocaine), maternal hypertension, depletion of amniotic fluid, long labor or difficult birth, or placental defects. Normally, the gastrointestinal system is not mature enough to pass meconium before 34 weeks of gestation, but due to distress, the fetal vagus nerve can activate gastrointestinal peristalsis and cause relaxation of the an_al sphincter, potentially resulting in meconium passage. The presence of meconium in the amniotic fluid can be recognized during childbirth when the amniotic sac ruptures, and the fluid appears greenish or yellowish. If meconium is aspirated with the first breath, it can lead to serious complications, such as labored breathing, barrel-shaped chest, or a low Apgar score. It is therefore crucial to aspirate meconium from the newborn's airways to prevent obstructions, surfactant dysfunction, pulmonary inflammation, or hypertension, all of which increase susceptibility to pulmonary infections, including pneumonia.