What is Ovulation? Top 7 Things You Might Not Know About It

“What is ovulation?” may seem like an easy question—it’s just when the egg is released, right? True, but there is so much more to ovulation than that. It’s the major turning point in the cycle, and understanding this process is key to getting pregnant fast.

Fact 1: Egg cells survive for 12 – 24 hours

Ovulation is when a mature egg is released from one of the ovaries. During the first half of the menstrual cycle, multiple follicles—fluid-filled sacs containing immature eggs—grow until one emerges as dominant. Eventually, the dominant one secretes estradiol (one of the main estrogens) which leads to a surge in luteinizing hormone (LH), causing the dominant follicle to rupture, and a mature egg is released.

Once the mature egg is released, though, it only survives for between 12 – 24 hours. So, the process of ovulation itself doesn’t last very long, but the complex biology leading to ovulation takes longer.

Fact 2: The best time to get pregnant is two days before ovulation

What is ovulation in the context of getting pregnant? Well, it’s not quite what you might have seen in movies and T.V. shows aka a woman frantically exclaiming that she’s ovulating so she must have sex at that exact moment or she won’t get pregnant.

Actually, a large study of over 7,000 menstrual cycles from 2000 showed that your chances of conceiving are highest during the 2 – 3 days before ovulation. As mentioned above, the actual moment of ovulation—when the egg is released from the ovary—takes only a moment. But, because the egg survives for a short time, your chances of conceiving are better if the sperm have already made their way up to the fallopian tube where they can readily fertilize the egg.

An earlier study from 1995 had similar findings, observing conception rates from couples who had intercourse during the fertile window. The conception rate was 36 percent two days before ovulation and 34 percent the day before ovulation. For comparison, intercourse three, four, or five days before ovulation had an 8 – 17 percent chance of conception.

Fact 3: Odds of conceiving on day of ovulation is… tricky

A study from 1998 assessed odds of conceiving on the day of ovulation, and the answer was tricky:  Intercourse on day of ovulation had a high conception rate, but it also had the higher rate of pregnancy loss. The researchers speculated that this potentially has to do with the fact that the egg has been around too long before sperm could successfully fertilize it, but more research is needed to know for sure.

Bottom line? Knowing your cycle is always a good idea for making the most of your fertility calendar so you can time intercourse as accurately as possible to know when the best time is to get pregnant.

Fact 4: Human Chorionic Gonadotropin (hCG) rescues the follicle after ovulation

Wondering what happens to the rest of the follicle after ovulation? After the mature egg awaits fertilization, the rest of the follicle becomes the corpus luteum, which secretes progesterone and maintains the built-up uterine lining. If implantation doesn’t occur, then the corpus luteum shrinks, progesterone levels drop, and your period begins.

BUT, if implantation occurs, then hCG levels will rise, “rescuing” the corpus luteum so that it can continue to secrete progesterone, supporting the uterine lining and leading to the missed period aka an early sign of possible pregnancy.

Fact 5: LH surges can vary from woman-to-woman

After the surge in LH, ovulation happens about 12 – 24 hours later. But, how long the LH surge lasts can vary considerably from woman to woman or even within the same woman from cycle to cycle. While researchers are still trying to understand why, it’s important to know that this variability can make it difficult to interpret at-home LH tests. If you have a short LH surge, you might miss the peak. If you have a long LH surge, you can get days of positive tests.

Fact 6: It’s possible to experience bleeding without ovulating

It’s possible to experience an anovulatory cycle, or a cycle with no ovulation. In this case, the uterine lining that was built during the first half of the cycle will still have to be shed, resulting in breakthrough bleeding. This type of bleeding will seem like a period, but it’s not a true period because ovulation didn’t occur.

Anovulatory cycles typically happen after a major shift in hormones, like after coming off hormonal birth control (as in the case of post-pill amenorrhea) or after giving birth. If you’re tracking basal body temperature and experience bleeding but no biphasic temperature change, it’s possible that you experience an anovulatory cycle. If you experience them recurrently, consult with your doctor about this issue.

Alternatively, it’s also kind of possible to ovulate without bleeding. A hormonal cascade of events means that bleeding almost always occurs roughly two weeks after ovulation (one exception to this is with the progestin-only methods of birth control such as the Mirena IUD, which thin uterine lining so that ovulation may occur without bleeding). But in the case of breastfeeding, for example, ovulation may precede menstruation. That means that if you’re breastfeeding, you might be fertile before the return of your period.

Fact 7: It’s possible to experience an LH surge but no ovulation

There is a condition called luteinized unruptured follicle syndrome, or LUF, and is a possible reason underlying unexplained infertility. It can happen occasionally to women with normal cycles, and for 6 – 25 percent of women with infertility.

What is ovulation in this case? In this condition, the LH surge doesn’t cause the follicle to rupture, so no egg is released aka no ovulation. But, the follicle will still secrete progesterone, so even though it’ll appear like a normal cycle, no ovulation occurs. Also, because the LH surge is still happening, urine LH tests for detecting ovulation will still appear positive. The only way to confirm if this condition happens is with ultrasound.

Aarthi Gobinath, PhD

Aarthi Gobinath earned her PhD in neuroscience from the University of British Columbia. Her research covers the ways that stress affects the male and female brain differently.

She tackled the issue of sex bias in research by looking at why standard treatments for depression don't always work in the case of postpartum depression. Her work has been covered by Vice and Massive Science.