The ovulatory phase is a point within the menstrual cycle when a mature egg is released from an ovary. This event is fundamental to reproduction, as the egg becomes available for fertilization by traveling down the fallopian tube. This phase is the culmination of hormonal changes that prepare the body for a potential pregnancy.
Hormonal Control of Ovulation
The regulation of ovulation is a process governed by hormones. During the preceding follicular phase, rising estrogen levels stimulate the growth of follicles within the ovaries. One follicle becomes dominant and continues to develop while the others are reabsorbed.
This dominant follicle produces a large amount of estrogen, which prepares the uterine lining. When estrogen levels peak, it signals the pituitary gland to release a large amount of Luteinizing Hormone (LH) in an event called the “LH surge.” This surge, along with a smaller increase in follicle-stimulating hormone (FSH), causes the dominant follicle to rupture and release the mature egg.
The ovulatory phase lasts 16 to 32 hours, with the egg released about 10 to 12 hours after the LH peak.
Timing Within the Menstrual Cycle
The timing of ovulation varies among individuals and from cycle to cycle. While a 28-day cycle often sees ovulation around day 14, a more precise way to estimate is to count backward 14 days from the start of the next period. For instance, in a 35-day cycle, ovulation would likely happen around day 21, while in a 21-day cycle, it could occur as early as day 7.
The period when conception is possible, the fertile window, includes the days leading up to and including ovulation. Sperm can survive in the female reproductive tract for several days, making the time just before the egg is released important for conception.
Physical Signs of Ovulation
The body provides several physical clues that ovulation is approaching. A common sign is a change in cervical mucus. As estrogen levels rise before ovulation, cervical mucus becomes clear, slippery, and stretchy, similar to raw egg whites. This change creates a more favorable environment for sperm to travel toward the egg.
Another sign is a shift in basal body temperature (BBT), the body’s lowest resting temperature. A slight but sustained increase in BBT, between 0.5 and 1 degree Fahrenheit, happens just after ovulation due to the release of progesterone. Because this occurs after the egg is released, tracking BBT confirms that ovulation has already taken place.
Some individuals experience one-sided pelvic pain around ovulation, known as mittelschmerz. This discomfort can range from a dull ache to a sharp pang and may last for a few minutes to a few hours on the side of the ovary releasing the egg. Other signs can include light spotting, breast tenderness, or an increased sex drive.
Conditions Affecting Ovulation
Several health conditions and lifestyle factors can disrupt ovulation, leading to irregular cycles or anovulation, which is a complete absence of ovulation. Polycystic Ovary Syndrome (PCOS) is a common hormonal imbalance that interferes with the development and release of eggs, often resulting in enlarged ovaries with multiple small cysts.
Hypothalamic dysfunction occurs when signals from the brain to the pituitary gland are impaired, affecting the release of LH and FSH. Premature ovarian insufficiency, where egg production stops early, can also prevent ovulation. Lifestyle factors, including significant stress, excessive exercise, and being either underweight or overweight, can impact the hormonal balance needed for regular ovulation.