So how does this work? Who determines the difference between 5 and 6 weeks?

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21. "DETERMINATION OF PRESENCE OF FETAL HEARTBEAT"

https://legiscan.com/TX/text/SB8/id/2395961

[...]

Sec. 171.203. DETERMINATION OF PRESENCE OF FETAL HEARTBEAT
REQUIRED; RECORD. (a) For the purposes of determining the
presence of a fetal heartbeat under this section, "standard medical
practice" includes employing the appropriate means of detecting the
heartbeat based on the estimated gestational age of the unborn
child and the condition of the woman and her pregnancy.
(b) Except as provided by Section 171.205, a physician may
not knowingly perform or induce an abortion on a pregnant woman
unless the physician has determined, in accordance with this
section, whether the woman's unborn child has a detectable fetal
heartbeat.
(c) In making a determination under Subsection (b), the
physician must use a test that is:
(1) consistent with the physician's good faith and
reasonable understanding of standard medical practice; and
(2) appropriate for the estimated gestational age of
the unborn child and the condition of the pregnant woman and her
pregnancy.
(d) A physician making a determination under Subsection (b)
shall record in the pregnant woman's medical record:
(1) the estimated gestational age of the unborn child;
(2) the method used to estimate the gestational age;
and
(3) the test used for detecting a fetal heartbeat,
including the date, time, and results of the test.
Sec. 171.204. PROHIBITED ABORTION OF UNBORN CHILD WITH
DETECTABLE FETAL HEARTBEAT; EFFECT. (a) Except as provided by
Section 171.205, a physician may not knowingly perform or induce an
abortion on a pregnant woman if the physician detected a fetal
heartbeat for the unborn child as required by Section 171.203 or
failed to perform a test to detect a fetal heartbeat.
(b) A physician does not violate this section if the
physician performed a test for a fetal heartbeat as required by
Section 171.203 and did not detect a fetal heartbeat.
(c) This section does not affect:
(1) the provisions of this chapter that restrict or
regulate an abortion by a particular method or during a particular
stage of pregnancy; or
(2) any other provision of state law that regulates or
prohibits abortion.

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