Stress Ulcers

Does anyone know the cause of stress ulcers in a neonate? My sister recently had a precip delivery and after 2 hours of returning home the baby was throwing up blood and was rushed to the PCCU for 3 days where he was diagnosed with 2 stress ulcers. She was told it was because of the precip delivery, but I am more concerned that it was because she was on aspirin therapy during her pregnancy for a clotting disorder.