Final answer:
Gestational age is best determined by a first trimester ultrasound because it uses specific, visible developmental milestones to establish a reliable gestational age. Ultrasound is preferred for its detailed and safe imaging capabilities, unlike other less reliable methods such as last menstrual period or fundal height.
Step-by-step explanation:
Gestational age is best determined by first trimester ultrasound. This method is highly accurate in the first trimester because it measures the clear and consistent developmental milestones visible on an ultrasound, such as crown-rump length. An ultrasound performed during this period can establish a reliable gestational age which is critical in assessing fetal growth and development.
Ultrasound imaging is the preferred technique for studying fetal growth and development due to its ability to produce detailed images of the fetus inside the uterus without using ionizing radiation. Through ultrasound, the physician can observe the fetus's structure, organs, and movements, facilitating the accurate assessment of its development stages and potential issues.
The determination of gestational age by other factors such as the last menstrual period, fundal height measurement, or quickening is less precise. The last menstrual period can be unreliable if the cycle is irregular or not remembered accurately, while fundal height measurement and quickening are subjective and variable. Therefore, which factor is most reliable for determining gestational age is clear—the first trimester ultrasound.