The study found the risks raises with every week a child is born short of full-term.
The risk was said to be 40 to 60 percent higher in babies born moderately preterm.
Full-term is considered 40 weeks and this study found babies born at 37 to 38 weeks had a 20 percent higher risk of having ADHD.
Scientists say the study proves that preterm births carry a significant risk and needs to be given more attention in neonatal care.
