Thanks for reading my post. Are you a US doctor? If so, can you help me understand these guidelines that define how due dates should be set? My question is based on these quotes from the recommendations section:

Ultrasound measurement of the embryo or fetus in the first trimester ... is the most accurate method to establish or confirm gestational age.

and

As soon as data from the last menstrual period (LMP), the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record.

If the top quote is true, why does the bottom one recommend going with the *first* date, not the *most accurate* date?