**Core Concept**
The most common cause of first trimester abortion is related to the imbalance of hormones, particularly progesterone, which is crucial for maintaining pregnancy. Progesterone supports the implantation of the fertilized egg in the uterus and maintains the pregnancy throughout the first trimester.

**Why the Correct Answer is Right**
The correct answer is related to the role of progesterone in maintaining pregnancy. Progesterone receptors are present in the endometrium, and the hormone helps in decidualization, which is essential for implantation of the blastocyst. In the first trimester, an imbalance of progesterone can lead to abortion. This can be due to various reasons such as luteal phase defect, where the corpus luteum does not produce enough progesterone, or it can be due to progesterone antagonist receptors in the uterus.

**Why Each Wrong Option is Incorrect**
**Option A:** Chromosomal abnormalities are a common cause of miscarriage, but they are more common in second trimester abortions.
**Option B:** Infections like listeriosis can cause abortion, but they are not the most common cause of first trimester abortion.
**Option C:** Uterine anomalies can cause recurrent miscarriages, but they are not the most common cause of first trimester abortion.

**Clinical Pearl / High-Yield Fact**
A luteal phase defect can be identified by a short luteal phase (less than 10 days) and low progesterone levels on the 21st day of a 28-day menstrual cycle.

**Correct Answer: D. Luteal phase defect.**