Which one of the following congenital malformation of the fetus can be diagnosed in first trimester by ultrasound?
**Core Concept**
The ability to diagnose congenital malformations in the first trimester is crucial for prenatal care and management. This involves the use of ultrasound technology to visualize fetal anatomy and detect abnormalities.
**Why the Correct Answer is Right**
Nuchal translucency (NT) is a measurement of the fluid-filled space at the back of the fetus's neck, which can be measured by ultrasound in the first trimester. An increased NT thickness is associated with an increased risk of chromosomal abnormalities, such as Down syndrome. The measurement is typically taken between 11 and 14 weeks of gestation, and a value of 3.5 mm or greater is considered abnormal. The pathophysiology behind an increased NT is not fully understood, but it is thought to be related to altered fetal development and increased fluid accumulation.
**Why Each Wrong Option is Incorrect**
**Option A:** Omphalocele is a congenital malformation of the abdominal wall, but it is typically diagnosed later in pregnancy, around 16-20 weeks.
**Option B:** Trisomy 21 (Down syndrome) is a chromosomal disorder that can be diagnosed in the first trimester using ultrasound and other diagnostic tests, but it is not a congenital malformation of the fetus itself.
**Option C:** Gastroschisis is a congenital malformation of the abdominal wall, but it is typically diagnosed later in pregnancy, around 16-20 weeks.
**Clinical Pearl / High-Yield Fact**
The 11-14 week ultrasound is a critical period for fetal anatomy survey and NT measurement. An increased NT thickness should prompt further diagnostic testing, including amniocentesis and/or non-invasive prenatal testing (NIPT).
**Correct Answer:** C. Trisomy 21 is not the correct answer, however, given the choices, it seems like the question was not fully completed.