This is abhorrent on a few points:
1) A doctor is lying to his or her patient.
2) It allows the circumvention of the law.
3) This could have serious, possibly fatal consequences for mother and/or child.
4) The doctor could choose to tell the mother of the birth defects only after she has passed the window of opportunity to abort. I'm under the impression that a woman has until the third trimester to abort. Isn't this a tad late to start any needed prenatal care? Not to mention it's rather cruel to the parents. Not even because a woman has indicated that she would abort (which isn't a justification for this law anyway), this is all because the doctor suspects she may consider it!
"Well everything looks great, you'll be having you're baby in three months, oh by the way, the child will probably be mentally handicapped. Best get crackin' on researching how to care for such a child. Congratulations!"