## **Core Concept**
The most common cause of first-trimester abortion is related to chromosomal abnormalities. These abnormalities can lead to non-viable pregnancies, which are then spontaneously aborted. The underlying principle here involves the critical role of genetics in early pregnancy viability.

## **Why the Correct Answer is Right**
The correct answer, **Chromosomal abnormalities**, is right because approximately 50-60% of first-trimester miscarriages are due to chromosomal anomalies in the embryo. These anomalies can include aneuploidy (having an abnormal number of chromosomes), polyploidy (having multiple sets of chromosomes), and other genetic imbalances. Such abnormalities usually occur due to meiotic errors during gametogenesis (spermatogenesis or oogenesis) and can render the embryo non-viable.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While uterine anomalies can contribute to recurrent pregnancy loss, they are not the most common cause of first-trimester abortion.
- **Option B:** Hormonal imbalances can play a role in pregnancy maintenance but are less commonly identified as the primary cause of first-trimester abortions compared to chromosomal abnormalities.
- **Option D:** Although infections can cause pregnancy loss, they are not as frequently associated with first-trimester abortions as chromosomal abnormalities.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the risk of chromosomal abnormalities leading to miscarriage increases with maternal age. This is because the risk of meiotic errors during oogenesis increases with age. Clinically, this is an important consideration in the management and counseling of pregnant women, especially those of advanced maternal age.

## **Correct Answer:** C. Chromosomal abnormalities