Curious???

Okay so i recently found out im pregnant (7 weeks) . Im 18 years old. As first time mothers we all tend to worry about the baby's health and the outcome of the baby especially when it's your first! So none of my family has ever had any chromosomal disorders nothing big. Neither on the fathers side so how can i be sure that my baby wont have a chromosomal disorder (down syndrome) or anything else??