Final answer:
Ultrasound Dating is the most accurate measurement available to determine gestational age.
Step-by-step explanation:
The most accurate measurement available to determine gestational age is Ultrasound Dating. Ultrasound dating uses sound waves to create images of the fetus and can accurately determine gestational age by measuring the size of the fetus. This method is more precise than relying on the Last Menstrual Period (LMP) or Fundal Height Measurement. Fetal Heart Rate Monitoring is not used to determine gestational age, but rather to monitor the health of the fetus during pregnancy.