What is the definition of "gestational age"?

The definition of "gestational age" refers specifically to the age of the fetus calculated from the first day of the last menstrual period (LMP). This method is commonly used because it provides a standardized way to estimate the timing of key events during pregnancy, including conception and due date. By counting from the LMP, healthcare providers can estimate the gestational age in weeks, which is critical for monitoring fetal development, planning prenatal care, and anticipating delivery.

While ultrasound can provide an estimate of the fetal age based on measurements taken during the exam, this is not the primary definition of gestational age. The duration of pregnancy measured in weeks does relate to gestational age, but it does not encompass the specific methodology used to determine it. Additionally, calculating the age of the fetus using information from prenatal visits may incorporate several assessment methods, but it still would not be considered the definition of gestational age itself. Thus, defining gestational age as the time from the first day of the last menstrual period is the most accurate and widely accepted understanding.