Crown-Rump length of 120 mm means the gestational age is :
**Core Concept**
The **crown-rump length (CRL)** is a measure used in embryology and fetal development to estimate the gestational age of an embryo or fetus. It measures the length from the top of the head (crown) to the bottom of the buttocks (rump). This measurement is crucial in the early stages of pregnancy for dating and assessing fetal growth.
**Why the Correct Answer is Right**
A CRL of 120 mm corresponds to a specific gestational age based on established growth charts and fetal development timelines. Typically, a CRL of 120 mm is associated with a gestational age of approximately 14 to 15 weeks, considering the average growth rate of a fetus during this period.
**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect if it suggests a gestational age that does not align with the expected growth pattern of a fetus.
**Option B:** Similarly, this option is incorrect if it does not match the gestational age corresponding to a CRL of 120 mm.
**Option C:** This option is also incorrect for the same reason, not aligning with the established fetal development milestones.
**Option D:** Assuming this is not the correct gestational age for a CRL of 120 mm, it would be an incorrect choice.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the CRL is most accurate for estimating gestational age in the first trimester, up to about 14 weeks. After this period, other measurements like the **biparietal diameter (BPD)** become more reliable for estimating fetal age.
**Correct Answer:** C. 14 weeks