**Core Concept:** Congenital malformations are structural abnormalities present at birth, resulting from abnormal fetal development. Oral anticoagulants, such as warfarin, are medications that interfere with blood clotting, increasing the risk of excessive bleeding during pregnancy.

**Why the Correct Answer is Right:** The correct answer, option D (Edwards syndrome), is a type of chromosomal abnormality that increases the risk of pregnancy complications. In the context of maternal use of oral anticoagulants, it represents a specific example of a congenital malformation associated with such treatments.

**Why Each Wrong Option is Incorrect:**

A. Down syndrome (Option A) is caused by trisomy 21 and is unrelated to oral anticoagulants.
B. Tetralogy of Fallot (Option B) is a congenital heart defect and is unrelated to oral anticoagulants.
C. Hypoplastic left heart syndrome (Option C) is a congenital heart defect and is unrelated to oral anticoagulants.

**Clinical Pearl:**

While maternal use of oral anticoagulants does not directly cause most of the wrong options, it increases the risk of miscarriage, stillbirth, and other complications due to its anti-coagulant effect. In such cases, the fetus may be exposed to abnormal blood clotting, leading to various congenital malformations like Edwards syndrome.

**Correct Answer:** D. Edwards syndrome (Trisomy 18)