- **Placental Aging:**  
  - After 42 weeks, the placenta may begin to function less efficiently, reducing the oxygen and nutrients delivered to the baby.

- **Fetal Distress and Meconium Aspiration:**  
  - A stressed baby is more likely to pass meconium into the amniotic fluid, which can be inhaled during birth, potentially leading to breathing problems.

- **Increased Risk of Stillbirth:**  
  - Post-term pregnancies carry a higher risk of stillbirth due to decreased placental function and other complications.

- **Labor Complications:**  
  - The baby may grow larger (macrosomia), which can lead to difficulties during labor, increasing the chances of birth injuries, prolonged labor, or the need for a cesarean section.

- **Maternal Risks:**  
  - There is an increased risk of postpartum hemorrhage and other complications related to an overextended pregnancy.

These factors are why healthcare providers often consider induction of labor if a pregnancy extends significantly beyond 42 weeks.