Whats the percentage that have birth defects?

Depends on definitn: Most accept the definition of bds as anatomical abnormalities, large or small, obvious or not that are present at birth.Some might include gene derived anomalies like extra fingers or metabolic issues like cystic fibrosis. Numbers for individual defects are easier to come by than inclusive numbers for this reason. (ie.Cleft lip, down syndrome) i've seen inclusive estimates from 3-6% for all bd's.

3 to 4 %: The comprehensive NIH study of 50,000 pregnancies with infants followed up to the age of 7 years revealed approximately 3 to 4 % major birth defects in the neonatal period (not including genetic disorders like cystic fibrosis), defined as a condition requiring surgery, causing a significant cosmetic problem, or a significant functional problem. By age 7 years, the percentage of affected was 7%