Explain the term "gestational age".

Gestational age is the term used to quantify the age of a fetus from the first day of the last menstrual period (LMP). This measurement is essential in obstetrics to assess the development of the fetus in utero, determine due dates, and monitor pregnancy progress. The calculation starts from the LMP rather than the date of conception because it provides a standardized reference point that is consistent among women, despite variations in individual cycles.

This method allows healthcare providers to estimate a more accurate timeline for fetal growth and development, as well as making essential decisions regarding prenatal care. By using the first day of the last menstrual period, clinicians can consider the typical gestational period of approximately 40 weeks, which is helpful for scheduling routine visits and ultrasound assessments.

The other options do not accurately define gestational age. Option A refers to the age of a fetus after birth, which is not relevant to gestational age. Option C discusses puberty, which is unrelated to fetal development. Option D, while somewhat related, does not specify that gestational age is calculated from the date of the last menstrual period, making it less precise than the correct option.