Earliest detectable congenital malformation by USG
**Core Concept**
The question is testing the earliest detectable congenital malformation by ultrasound (USG) in a fetus. This involves understanding the development stages and the capabilities of ultrasound technology in detecting fetal abnormalities.
**Why the Correct Answer is Right**
The correct answer is **A. Nuchal Translucency (NT)**. Nuchal translucency is an increase in the thickness of the fluid-filled space at the back of the fetus's neck, which can be detected by ultrasound as early as 11 weeks of gestation. This is a significant risk factor for chromosomal abnormalities such as Down syndrome. The measurement of NT is a crucial part of the first trimester screening for Down syndrome and other fetal abnormalities.
**Why Each Wrong Option is Incorrect**
* **Option B:** Anencephaly is a congenital malformation where a large part of the brain and skull are absent. While it is detectable by ultrasound, it is typically detectable later than NT, around 14-16 weeks of gestation.
* **Option C:** Omphalocele is a congenital malformation where the intestines or other organs protrude through the navel. It is detectable by ultrasound, but typically later than NT, around 16-20 weeks of gestation.
* **Option D:** Cystic Hygroma is a congenital malformation of the lymphatic system, which can be detected by ultrasound. However, it is typically detectable later than NT, around 16-20 weeks of gestation.
**Clinical Pearl / High-Yield Fact**
The first trimester screening for Down syndrome includes the measurement of Nuchal Translucency (NT), maternal age, and serum markers such as free beta hCG and PAPP-A. A high NT is a significant risk factor for chromosomal abnormalities, and further testing such as non-invasive prenatal testing (NIPT) or amniocentesis may be recommended.
**Correct Answer:** A. Nuchal Translucency (NT)