(a) This section applies only to an abortion authorized under Section 171.046(a)(1) or (2) in which:
(1) the probable post-fertilization age of the unborn child is 20 or more weeks; or
(2) the probable post-fertilization age of the unborn child has not been determined but could reasonably be 20 or more weeks.
(b) Except as otherwise provided by Section 171.046(a)(3), a physician performing an abortion under Subsection (a) shall terminate the pregnancy in the manner that, in the physician's reasonable medical judgment, provides the best opportunity for the unborn child to survive.