Many people have grown up believing that the days immediately following their period are completely “safe” when it comes to the risk of pregnancy, but fertility experts say that assumption can be seriously misleading. Dr. Erika Munch, a fertility specialist, points out that while many women ovulate roughly two weeks before their next period, some can ovulate much earlier, which means the post-menstruation window is far from risk-free. As Dr. Munch explains, “Sperm in the body can survive up to five days, so if you have unprotected sex right after your period, pregnancy is still possible.” This is not just a harmless misconception — it can lead to unintended pregnancies or frustrate those who are actively trying to conceive, according to Today’s Parent.
To truly understand why this is the case, it helps to have a solid grasp of how the menstrual cycle actually works. Elisabeth van der Wilt, a doula and women’s health advisor, describes it this way: “Think of the menstrual cycle as your body’s monthly preparation for a possible pregnancy.” The cycle begins with the uterine lining thickening as an egg gets ready to be released from the ovary, all while a team of hormones works in the background to keep everything in sync. On average, a full cycle lasts somewhere between 25 and 35 days, though this varies from person to person, and menstruation itself typically lasts between two and seven days.
The cycle can be broken down into four distinct phases. The first is menstruation, when the uterus sheds its lining and bleeding occurs. This is followed by the follicular phase, during which the ovaries begin preparing an egg for release and the uterine lining starts rebuilding itself. Then comes ovulation, the moment a mature egg is released from the dominant follicle in the ovary. Van der Wilt notes that “ovulation is brief, usually lasting only 24 hours, but it’s the pivotal moment of the cycle.” Finally, the luteal phase begins after ovulation, during which the corpus luteum forms and releases hormones like progesterone to prepare the uterus for a potential pregnancy.
Several key hormones govern this entire process. FSH, or follicle-stimulating hormone, is released by the pituitary gland and encourages egg growth while raising estrogen levels. LH, or luteinizing hormone, also from the pituitary gland, is what actually triggers ovulation and helps transform the remaining follicle into the corpus luteum. Progesterone thickens the uterine lining after ovulation to ready it for a fertilized egg, and if pregnancy does not occur, its levels drop and menstruation begins again. Estrogen, produced by developing egg cells, helps build the uterine lining and peaks just before ovulation.
So what exactly is the fertile window? Dr. Eve Feinberg, a gynecologist and specialist in reproductive endocrinology, explains that the fertile window is the period during a cycle when conception is realistically possible. “It typically spans six days — the five days leading up to ovulation and the day of ovulation itself,” she says. Because sperm can remain viable in the body for up to five days, perfectly timed intercourse is not strictly necessary. “If sex occurs up to five days before ovulation, sperm can stay alive long enough to fertilize the egg. But once the egg is released, it only has about 24 hours to be fertilized,” Dr. Feinberg adds.
As for whether pregnancy is genuinely possible right after a period ends, Dr. Ruchi Amin, a reproductive endocrinologist, confirms that it is, and that the likelihood depends heavily on cycle length. “If someone has a shorter cycle, there may be only a few days between the end of their period and the start of their fertile window, which can increase the chances of pregnancy,” she notes. She also points out that as women age, their bodies can begin preparing eggs earlier in the cycle, sometimes during the final days of the previous cycle, which can result in earlier ovulation.
It is worth understanding a few broader facts about menstrual health that provide helpful context here. The menstrual cycle is regulated by a complex hormonal feedback loop involving the hypothalamus, pituitary gland, and ovaries, sometimes referred to as the HPO axis. Cycle length and ovulation timing can be significantly affected by stress, body weight changes, illness, intense exercise, and certain medications. Conditions such as polycystic ovary syndrome (PCOS) can cause irregular ovulation, making cycle tracking even less predictable. For anyone trying to conceive or avoid pregnancy, ovulation predictor kits, basal body temperature tracking, and cervical mucus monitoring are commonly recommended tools that provide more reliable information than calendar-based methods alone.
If this topic has made you think differently about how your own cycle works, feel free to share your experience or questions in the comments.
