Understanding ovarian physiology is key to understanding ovarian factors that play a role in infertility. At birth, each ovary has approximately one million eggs. Each egg is protected by a layer of cells called a “primordial follicle”, a portion of which develop into “antral follicles.” Antral follicles mature under the influence of the hormone produced by the pituitary gland called follicle-stimulating hormone (FSH).
Normal Ovulatory Cycle
The normal cycle is broken down into follicular and luteal, or post-ovulatory, phases. During the follicular phase, antral follicles are subjected to higher levels of FSH causing them to begin the maturation process. Usually, several follicles start to grow and release estrogen. However, as they grow FSH declines. Consequently, only one follicle continues to grow. When that follicle and its corresponding egg reach maturity, luteinizing hormone, or LH, is released from the pituitary as a “surge” of activity; this is responsible for egg release from the follicle as well as the initiation of progesterone production by the follicle. The luteal phase lasts 14 days and is characterized by high progesterone levels relative to the follicular phase.
A blood progesterone level is drawn 7 days after the presumed day of ovulation to determine if ovulation is occurring. In a typical 28-day cycle, this is on cycle day 21 but, not all normal cycles are 28 days. So, your progesterone level draw will be determined by your particular cycle length.
An ovulatory progesterone level can range from 5 to 15 ng/ml. A single progesterone level can determine if you have ovulated, but not if your luteal phase is normal. To do this, we use a “pooled progesterone level” that combines blood drawn on 3 consecutive days in the luteal phase. A pooled progesterone level greater than 10 ng/ml suggests a normal luteal phase.
The term “ovarian reserve” refers to the age-related aspect of ovarian function. No new eggs are generated after embryonic ovarian development. As a woman ages, her eggs age as well. As eggs age, the “machinery” required for normal division of chromosomes begins to deteriorate. This accounts for the increase in infertility, miscarriage and chromosomally abnormal offspring as women age. These tests assess ovarian reserve:
- Cycle day 3 FSH and estradiol level
- Antimullerian Hormone level (AMH)
- Antral follicle count (AFC)
On cycle day 3 (CD3), the third day of full menstrual flow, the ovaries are normally at rest and estradiol is low.
Day 3 FSH Level in relation to Ovarian Reserve*
*assumes simultaneous D-3 estradiol is <50pg/ml
|Ovarian Reserve||FSH Levels|
|Severe Decrease||> 15
|Ovarian Reserve||FSH Levels|
|Severe Decrease||> 15|
AMH, antimullerian hormone, is produced by the primordial follicles and declines with age as the primordial follicles are “used up”. In the reproductive years, AMH is expected to be between 1 and 5 ng/ml. A level lower than 1 indicates that the ovary is becoming depleted of primordial follicles.
The number of antral follicles is proportional to the number of follicles in the whole ovary, so an Antral Follicle Count (AFC) can provide important information. We expect to see between 5 and 10 antral follicles in each ovary at any given time. If there are fewer than 5 in an ovary, it tells us two things: First, the ovary is becoming depleted of follicles and second, our ability to obtain multiple eggs by ovarian stimulation is limited thus limiting our treatment options.