My wife and I went through exactly the same, almost 10 years ago. Quite a few medical offices are STRONGLY biased in favor of abortion for indications of Downs.
We had the same error in test results too, and I think a DELIBERATE mistake as to the date of pregnancy, which gives a false positive on AFP test. The doctors told us we were wrong about the date of pregnancy - they insisted we were wrong. And we knew for a fact that we were not.
We told 'em to stuff it - the extra tests, the attitude, and the business. We fired the doctor. We hired a midwife - had the baby at the Catholic hospital.