**Core Concept**
Chromosomal abnormalities are a leading cause of early pregnancy loss, often resulting in spontaneous abortion during the first trimester. This is due to errors during meiosis, leading to aneuploidy or other genetic issues that compromise fetal development.

**Why the Correct Answer is Right**
The correct answer is related to chromosomal abnormalities, which occur during meiosis when genetic material is not properly segregated. This can result in aneuploidy, where the fetus has an abnormal number of chromosomes. The most common chromosomal abnormalities leading to first-trimester abortion include trisomy 16, trisomy 13, and trisomy 18. These conditions often arise from errors during meiosis, particularly non-disjunction, where pairs of chromosomes fail to separate properly.

**Why Each Wrong Option is Incorrect**
**Option A:** Although hormonal imbalances can contribute to early pregnancy loss, they are not the most common cause of first-trimester abortion.
* Hormonal imbalances can lead to issues like luteal phase defect, but they are less common compared to chromosomal abnormalities.

**Option B:** Infections like listeriosis can cause miscarriage, but they are relatively rare causes of first-trimester abortion.
* Infections like listeriosis can cause miscarriage, but they are not the most common cause of first-trimester abortion.

**Option C:** Uterine anomalies are a rare cause of early pregnancy loss and are not the most common cause of first-trimester abortion.
* Uterine anomalies, such as a bicornuate uterus, can contribute to pregnancy complications, but they are not the most common cause of first-trimester abortion.

**Clinical Pearl / High-Yield Fact**
It's essential to note that chromosomal abnormalities are a leading cause of early pregnancy loss, and the risk of aneuploidy increases with maternal age. This highlights the importance of genetic counseling and screening for women over 35 years old.

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