**Core Concept**
Edward syndrome, also known as Trisomy 18, is a genetic disorder caused by an extra copy of chromosome 18. Accurate diagnosis is crucial for managing the condition and providing appropriate care to patients and their families.

**Why the Correct Answer is Right**
The investigation performed here to diagnose Edward syndrome is likely a **Chorionic Villus Sampling (CVS)** or **Aminocentesis**, which involves analyzing the genetic material from the placenta or amniotic fluid to detect chromosomal abnormalities. These prenatal tests allow for early detection of Trisomy 18, enabling expectant parents to make informed decisions about their pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** **Ultrasound** is a valuable diagnostic tool for detecting structural anomalies and fetal growth restrictions associated with Edward syndrome, but it is not a definitive diagnostic test for chromosomal abnormalities.

**Option B:** **Coombs test** is a blood test used to detect autoimmune disorders such as Rh incompatibility, which can cause hemolytic disease of the newborn, but it is not relevant to diagnosing chromosomal abnormalities like Edward syndrome.

**Option C:** **Karyotype analysis** is a laboratory test that examines the chromosomes in a person's cells, but it is not a specific investigation for diagnosing Edward syndrome, as it can detect a wide range of chromosomal abnormalities.

**Clinical Pearl / High-Yield Fact**
Prenatal diagnosis of Edward syndrome can be challenging, and a definitive diagnosis is often made postnatally through chromosomal analysis of blood or tissue samples. Accurate diagnosis is crucial for providing supportive care and counseling to families affected by this condition.

**Correct Answer: D. Aminocentesis. Aminocentesis is performed to diagnose Edward syndrome.**