i am not sure but i just wonder, my sister doesn't have any vices, she takes care of herself and she's very careful but still she gave birth with defects.
Genetics play a role in some birth defects. Every cell in the body has chromosomes containing genes that go a long way in determining a person's unique characteristics. One missing or faulty gene can cause a birth defect; this is significant when you consider that we each have about 25,000 genes per cell determining everything from the length of our toes to the color of our eyes.