Final answer:
The crown-rump length measurement during the first trimester is the most reliable method for determining gestational age, with the second trimester ultrasound also being highly accurate.
Step-by-step explanation:
The most reliable method of determining the gestational age of a fetus is the crown-rump length measurement during the first trimester. This is due to the fact that there is less variability in fetal size during the early stages of pregnancy. During the second trimester, a second trimester ultrasound is still considered highly accurate, especially when assessing fetal anatomy and confirming earlier measurements. Quickening date, while meaningful to the expectant mother, is not scientifically reliable as it is subjective. Third trimester composite biometry can also help estimate gestational age, but due to the increased variability in fetal size at this stage it is less precise. Lastly, placental calcifications are a normal part of the aging placenta but are not a precise indicator of gestational age.
Ultrasound imaging remains the technique of choice for studying fetal growth and development throughout pregnancy because it provides detailed images of the fetus, allows for measurements of fetal parts such as the head, abdomen, and femur, and has no known adverse effects when used appropriately.