Earliest detectable congenital malformation by USG is :
First, I remember that early detection in pregnancy is crucial. USG is a primary tool here. The first trimester is when some anomalies can be detected. The most common early malformations include neural tube defects, cardiac issues, and limb abnormalities. But which one is the earliest?
Neural tube defects like anencephaly are usually detected around 12-14 weeks. Cardiac defects might be seen as early as 10-12 weeks with fetal echocardiography. Limb abnormalities such as absence of a limb might be visible by 12 weeks. However, the earliest is likely anencephaly because the neural tube closes by around 6-7 weeks, so any defect would be apparent by the end of the first trimester. But wait, some sources say that anencephaly can be detected as early as 11-12 weeks. Another possibility is gastroschisis or omphalocele, but those are abdominal wall defects. Gastroschisis is usually picked up by 12 weeks.
Wait, the earliest would be anencephaly because the neural tube closes early, so absence of the skull bones and brain tissue would be visible by 12-14 weeks. However, some sources suggest that certain cardiac anomalies like hypoplastic left heart syndrome can be detected as early as 10-12 weeks. But the question is about the earliest detectable congenital malformation. So maybe the answer is anencephaly. Alternatively, limb abnormalities like absence of the femur could be seen by 12 weeks. But I need to confirm the standard answer here.
Looking up standard textbooks, the earliest detectable congenital malformation by USG is anencephaly, typically around 12 weeks. Other options like spina bifida might be detected later, around 18-20 weeks. So the correct answer is anencephaly. The other options would be incorrect because they are either detected later or not the earliest. The clinical pearl here is to remember that neural tube defects are among the earliest to detect due to the timing of neural tube closure.
**Core Concept**
The earliest detectable congenital malformation by ultrasound (USG) is determined by the timing of organogenesis and the structural complexity of the defect. Neural tube defects, such as anencephaly, are typically identified earliest due to their gross anatomical disruption and the timing of neural tube closure (6–7 weeks gestation).
**Why the Correct Answer is Right**
Anencephaly, a severe neural tube defect, is the earliest detectable congenital malformation by USG, usually visible by 12–14 weeks. It results from failure of the cranial neural tube to close, leading to absence of the skull and brain tissue. The absence of the calvarium and characteristic "lemon sign" (rounded, collapsed skull) are easily visualized sonographically, even before other malformations become apparent. Early detection is critical for counseling and management.
**Why Each Wrong Option is Incorrect**
**Option A:** Spina bifida is detectable later (1