North American Registry of Midwives (NARM) Practice Exam

During which phase of the reproductive cycle does the endometrial lining thicken?

1. Follicular phase

2. Luteal phase

3. Ovulation phase

4. Menstrual phase

The correct answer is: Luteal phase

The thickening of the endometrial lining occurs during the luteal phase of the reproductive cycle. This phase begins after ovulation and typically lasts about 14 days, leading up to the next menstrual period. During this phase, the corpus luteum, which forms from the ruptured follicle, secretes hormones, primarily progesterone. Progesterone plays a critical role in preparing the endometrium for a potential implantation of a fertilized egg. The increase in progesterone levels is responsible for making the endometrial lining more vascular and glandular, which is essential for supporting an early pregnancy if conception occurs. In contrast, other phases such as the menstrual phase involve the shedding of the endometrial lining, while the follicular phase is focused on the development of follicles and the preparation for ovulation. The ovulation phase marks the release of the egg from the follicle but does not contribute to the thickening of the endometrial lining. Thus, the luteal phase is distinctly characterized by the preparation of the uterus for potential implantation, which is why this is the correct answer.