Ovulation is the release of a mature egg from the ovary, marking the end of the follicular phase and the beginning of the fertile window. Knowing when the body transitions into an infertile state is important for family planning, whether aiming for conception or avoidance. Once ovulation is complete, the egg’s short lifespan means the fertile window closes quickly. The body then exhibits distinct physical and hormonal signs that confirm this shift has occurred.
Basal Body Temperature Confirmation
The most definitive sign that ovulation is over is a sustained increase in the body’s lowest resting temperature, known as the Basal Body Temperature (BBT). This temperature shift confirms that ovulation has successfully taken place, as it is caused by the sudden dominance of the hormone progesterone.
After the egg is released, the empty follicle transforms into the corpus luteum, which produces large amounts of progesterone. This hormone acts on the hypothalamus, the body’s temperature-regulating center, causing the BBT to rise slightly. The temperature increase typically ranges from 0.4 to 1.0 degrees Fahrenheit (0.2 to 0.6 degrees Celsius) above the pre-ovulatory average.
To accurately track this shift, BBT must be measured at the same time every morning immediately upon waking, before any activity. A specialized basal thermometer, which measures to at least one-tenth of a degree, is necessary to detect this subtle change. Confirmation requires observing three consecutive daily temperatures that are all higher than the previous six low temperatures.
This sustained temperature plateau confirms that the fertile window has closed. The elevated temperature remains constant throughout the luteal phase until progesterone levels drop just before menstruation begins. If the BBT remains elevated for more than 18 days past the confirmed ovulation date, it can indicate pregnancy.
Changes in Cervical Mucus and Position
Physical changes in the cervix and the quality of cervical mucus provide observable signs that the body has moved from a fertile to an infertile state. The cervix, the lower part of the uterus, changes its texture, position, and openness throughout the cycle in response to fluctuating hormones.
Before and during ovulation, rising estrogen levels cause the cervical mucus to become clear, wet, slippery, and stretchy, often compared to raw egg whites. This consistency is sperm-friendly, allowing sperm to travel easily toward the egg. Once ovulation occurs, the increase in progesterone signals a rapid change in the mucus.
The mucus quickly transitions to a thick, sticky, tacky, or completely dry consistency, effectively closing the pathway to the uterus. This post-ovulatory mucus acts as a barrier, becoming hostile to sperm survival and movement. The presence of this sticky mucus confirms that the fertile time has ended.
The cervix itself also undergoes a noticeable transformation after ovulation. During the fertile window, it is typically high, soft to the touch, and the opening is open. Following ovulation, the cervix drops lower, becomes firmer—often feeling like the tip of the nose—and the opening closes tightly. This low, firm, and closed position reinforces the physical barrier created by the thick mucus.
Understanding the Luteal Phase Duration
The final confirmation that the fertile window is closed comes from understanding the fixed timing of the luteal phase, which begins immediately after ovulation. The luteal phase is defined as the time from confirmed ovulation until the start of the next menstrual period.
This phase is consistent in length, typically lasting between 12 and 16 days. While the follicular phase can vary significantly, the luteal phase generally remains stable for an individual. This fixed duration is determined by the lifespan of the corpus luteum, the temporary structure that produces progesterone.
Once ovulation is confirmed by a sustained BBT shift or changes in cervical signs, the remaining days of the luteal phase are considered infertile. This predictable timing allows for a reliable calculation of the end of the fertile window. A luteal phase lasting at least 10 days is considered normal and healthy.