What is the most reliable method to determine a baby's age?

A sonogram, or ultrasound, is considered the most reliable method for determining a baby's age because it provides direct visual assessment of the fetus in utero. The measurements taken during a sonogram, such as the crown-rump length in the first trimester or the biparietal diameter and femur length in later trimesters, offer accurate estimates of gestational age. These measurements are based on established growth patterns and norms for fetal development, making them a vital tool in prenatal care.

In contrast, palpation involves the healthcare provider feeling the mother's abdomen to assess fetal position and gestational age, but this method can be subjective and less precise. A gestational wheel is a helpful tool that estimates gestational age based on the last menstrual period but does not account for variations in individual fetal development or anomalies. Fetal heart rate monitoring provides important information about the baby's well-being but does not directly indicate gestational age. Therefore, sonograms are the most dependable method for accurately determining a baby's age.