The Role of Hormones in the Fertility Cycle
A woman's fertility cycle, also known as the menstrual cycle, typically ranges from 24 to 38 days [8].
The rise and fall of hormone levels drive the development of the menstrual cycle. Understanding the process can help you understand your fertility and what tests or treatments may help.
Menstruation
The fertility cycle begins with the menstrual bleeding phase, clinically known as the follicular phase. Two key processes occur during this phase.
One is the shedding of the endometrium, the thickened uterine lining that develops to prepare for embryo implantation. Low levels of estrogen and progesterone drive this process.
At approximately the same time, FSH levels increase, prompting the growth of a cohort of ovarian follicles. One of those follicles becomes dominant and secretes high estrogen levels to prepare for ovulation [9].
Ovulation
Rising estrogen levels cause a surge in FSH and LH. The LH surge stimulates egg release from the dominant follicle, usually 16 to 32 hours after the initial hormonal surge [8].
At the same time, estrogen levels decrease, and progesterone increases. LH levels fall significantly after ovulation is complete [9].
Luteal Phase
The luteal phase begins at ovulation and lasts approximately 14 days [9]. During this time, non-released follicular cells combine with other cells in the ovaries to become a hormone-releasing organ called the corpus luteum, which releases progesterone to prepare for and maintain pregnancy.
Progesterone is the hormone that prepares the uterine lining for pregnancy by creating new capillaries. Peak blood flow happens around nine days after ovulation when progesterone and estrogen are also at peak levels. At that time, the uterus is preparing for potential fertilization [10].
If pregnancy occurs, the body will release HCG to keep the corpus luteum active. If not, the structure dissolves, and estrogen and progesterone decrease. This begins menstruation and the cycle restarts.
Menopause
In the absence of a medical disorder or surgical interruption, a woman's fertility cycle continues until menopause. Menopause is not a moment in time but a multi-year transition during which reproductive hormones fluctuate dramatically.
These hormonal fluctuations lead to changes in the timing of a woman's fertility cycle. Those changes typically begin four to eight years before a woman's last period [11].
Most women experience menopause between 46 and 55 years of age. Menopause is premature before age 40 and early but normal between 41 and 45.
How Hormonal Imbalances Impact Fertility
Hormones prompt the chemical reactions that drive the fertility cycle. If hormone levels are abnormal, it can affect a woman's ability to conceive. For example:
- Low FSH levels may indicate a failure of the ovaries to produce and release eggs [12]
- Low LH at ovulation may reduce the chances of conception [13]
- Low progesterone or impaired progesterone reactions may prevent a successful pregnancy [14]
If you have concerns about your fertility or have had trouble getting pregnant, an evaluation of your fertility hormones could offer answers.
Testing and Monitoring Fertility Hormones
Hormone testing is a common way of monitoring and assessing fertility. Many women test at home using over-the-counter products.
One famous example is the urine test for ovulation production, which measures LH levels. These measure the LH surge that precedes ovulation [15]. Another option is the PdG test.
But what is a PdG test? This option is newer, and many women are still unfamiliar with it.
The PdG test evaluates progesterone levels to confirm ovulation. Because PdG levels change after the LH surge, a PdG test can offer results during the fertility window [16].
Clinics and physicians' offices may also do urine or blood testing to evaluate fertility hormones [17]. A healthcare provider will choose the most appropriate tests based on an interview and physical exam.
Follow the Diagnox blog to learn more about at-home medical testing and how it can help you take control of your health.
