Admin_NHT Staff asked 6 years ago Meconium Aspiration Syndrome (MAS) affects new-born babies. Babies sometimes pass meconium (or stool) in the amniotic fluid at the time of labour or delivery or in high stress situations, and the baby sometimes breaths in this fluid. This fluid build-up in the baby’s lung leads to MAS. The meconium blocks the baby’s airways, which causes a swelling of the baby’s lungs, which leads to breathing problems. Factors that can induce stress on baby before birth include : Aging of placenta, decreased supply of oxygen to the womb, mother having diabetes or high blood pressure, or a really long labour.