About 1 in 33 babies is born with a birth defect
That is the starting point, before any test is done. No test brings it to zero.
Most people begin a pregnancy with a private assumption that serious problems are rare and happen to other people. The first half of that is not quite true.
CDC states it in two sentences: Birth defects are common, affecting 1 in every 33 babies born in the United States each year.
And: They are also the leading cause of infant deaths, accounting for 20%, or 1 in 5, of all infant deaths.
Behind that headline is the oldest US surveillance system for birth defects, which has been counting in metropolitan Atlanta since 1978. Its finding: the overall prevalence of major defects was stable from 1978 (2.8 per 100 live births) to 2005 (3.0 per 100).
Note that this is one metropolitan area, not a national register. The 1 in 33 is CDC's own rounded headline and is safe to use as CDC's figure, attributed that way.
An independent US count, from statewide surveillance in Utah of children born 2005 to 2009, found 5,504 major birth defects among 270,878 births, a rate of 2.03%. That study excluded mild isolated conditions (such as muscular ventricular septal defects, distal hypospadias)
. The two figures are not a disagreement. They are two different definitions of what counts.
On infant death, a national analysis found that birth defects accounted for 20.6% of US infant deaths in 2017, and that the rate of infant death attributable to birth defects fell from 12.2 per 10,000 live births in 2003 to 11.0 per 10,000 in 2017. Those authors state that breaking this down by type of defect was outside what they studied, so no claim of the form "heart defects cause this much of it" can be made from this source.
"Does my test result change that number, and by how much?"