**Question:** Most common cause of Moebius syndrome in use of which of the following drug in pregnancy?

**Core Concept:** Moebius syndrome is a congenital disorder characterized by the absence of facial muscles and abnormal limb movements. It is mainly caused by exposure to teratogenic drugs during pregnancy. Teratogenic drugs are substances that can cause birth defects in a developing embryo or fetus.

**Why the Correct Answer is Right:** The correct answer, "D-Thalidomide", is due to its strong teratogenic properties. Thalidomide is an antiemetic (anti-nausea) drug that was widely prescribed for morning sickness during pregnancy in the 1950s and 1960s. Unfortunately, it caused severe birth defects in thousands of babies, including Moebius syndrome.

**Why Each Wrong Option is Incorrect:**

A. **Dicumarol (Warfarin)** is an anticoagulant used to prevent blood clots. It is not a teratogenic drug, making it an incorrect choice.

B. **Salicylic Acid (ASA)** is a nonsteroidal anti-inflammatory drug (NSAID) commonly used for pain relief and fever reduction. While it can cause some fetal abnormalities, it is not the most common cause of Moebius syndrome.

C. **Anti-histamines (e.g., Cetirizine)** are used to treat allergies and are not a strong teratogen like Thalidomide. They are also less likely to cause Moebius syndrome compared to Thalidomide.

**Clinical Pearl:** Teratogenic drugs can have severe and permanent consequences for the developing fetus, emphasizing the importance of avoiding certain medications during pregnancy and counseling patients appropriately.

**Correct Answer:** D. Thalidomide