Nuchal translucency is best measured at-
**Question:** Nuchal translucency is best measured at-
A. 10th week of pregnancy
B. 11th week of pregnancy
C. 12th week of pregnancy
D. 13th week of pregnancy
**Core Concept:** Nuchal translucency (NT) measurement is a non-invasive ultrasound procedure used to assess the risk of trisomies, particularly Down syndrome, in early pregnancy. It measures the distance between the skin and underlying fluid at the back of the neck, which is thicker in fetuses with increased risk of chromosomal abnormalities.
**Why the Correct Answer is Right:** The optimal time for measuring nuchal translucency is during the first trimester, typically between 11 to 14 weeks of pregnancy. The 12th week is a more precise time point due to the decreased variability in measurement and increased sensitivity for detecting trisomy 21 (Down syndrome).
**Why Each Wrong Option is Incorrect:**
A. Measuring nuchal translucency earlier than 11 weeks is not recommended as the fetal structures are not fully developed, leading to unreliable measurements and reduced sensitivity for detecting chromosomal abnormalities.
B. Measuring nuchal translucency later than 14 weeks is not ideal due to fetal growth and anatomic changes that can affect the measurement accuracy and reduce the sensitivity of the test.
C. While measuring the nuchal translucency at 12 weeks is optimal, measuring it at 13 weeks is also reasonable as it falls within the recommended time frame and provides a more accurate measurement due to fewer technical errors.
D. Measuring nuchal translucency at 13 weeks is incorrect, as it is just one week later than the optimal measurement period and may still be affected by fetal growth and anatomic changes.
**Clinical Pearl:**
Measuring nuchal translucency at the 12th week of pregnancy is crucial for accurate assessment of fetal chromosomal abnormalities, particularly trisomy 21. This test helps healthcare providers in counselling pregnant women about the risk of chromosomal abnormalities and guiding appropriate further testing and management strategies.