Best marker of gestational age in 2nd trimester is :
**Core Concept**
The determination of gestational age is crucial in prenatal care, particularly in the second trimester when ultrasound measurements become more accurate. The best marker of gestational age in this period is an important diagnostic tool for obstetricians.
**Why the Correct Answer is Right**
The correct answer is the femur length (FL). In the second trimester, the femur length is a reliable indicator of gestational age because it grows at a steady rate. The femur length is measured from the top of the greater trochanter (the large rounded prominence at the top of the femur) to the bottom of the femur. This measurement is taken using ultrasound and is expressed in centimeters. The femur length is used in conjunction with other ultrasound markers, such as the biparietal diameter (BPD), to estimate gestational age.
**Why Each Wrong Option is Incorrect**
* **Option A:** The biparietal diameter (BPD) is an important marker of gestational age, but it is not the best marker in the second trimester. BPD measures the distance between the two parietal bones of the fetal skull and is more accurate in the first and third trimesters.
* **Option B:** The abdominal circumference (AC) is a useful marker of fetal growth and development, but it is not the best marker of gestational age in the second trimester.
* **Option C:** The head circumference (HC) is an important marker of fetal growth and development, particularly in the first and third trimesters, but it is not the best marker of gestational age in the second trimester.
**Clinical Pearl / High-Yield Fact**
The femur length is a reliable marker of gestational age because it grows at a steady rate, making it a useful tool for obstetricians to estimate gestational age in the second trimester. This information can be used to monitor fetal growth and development and to identify any potential complications.
**Correct Answer:** C. Femur length.