Ovulation is the release of an egg from one of a woman’s ovaries. After the egg is released, it moves down the fallopian tube, where fertilization by a sperm cell can take place.
Ovulation usually lasts one day and occurs in the middle of a woman’s menstrual cycle, about two weeks before she expects to have her period. But the timing of the process differs for each woman, and it may even differ from month to month.
If a woman is hoping to get pregnant, she will want to keep up with when she might be ovulating. Knowing when a woman ovulates each month is helpful because she is most fertile – or able to conceive – around the time of ovulation.
A couple will be more likely to get pregnant if they have sex a day or two before a woman ovulates and the day of ovulation, according to the March of Dimes.
Menstrual cycle and ovulation
At birth, a female fetus has 1 to 2 million immature eggs called oocytes in her ovaries, which are all the eggs she will ever produce, according to the Cleveland Clinic. By the time a girl enters puberty, about 300,000 of these eggs are left. About 300 to 400 of the remaining eggs will be ovulated during a woman’s reproductive life, says the Cleveland Clinic.
A likely sign that a woman is ovulating is that she has regular, predictable periods that occur every 24 to 32 days, according to the Centers for Disease Control and Prevention (CDC).
With each monthly menstrual cycle, a woman’s body prepares for a possible pregnancy. The cycle is regulated by hormones, including the sex hormones estrogen and progesterone, as well as follicle-stimulating hormone and luteinizing hormone. Hormones play a key role in all stages of the menstrual cycle, allowing the ovum (egg) to mature and eventually be released.
When an adult ovum leaves a woman’s ovary and moves into the fallopian tube, a sperm cell can fertilize the ovum. Sperm can live inside a woman’s reproductive tract about 3 to 5 days after sexual intercourse, according to the Mayo Clinic. For pregnancy to occur, a sperm cell must fertilize the egg within 12 to 24 hours of ovulation, according to the Mayo Clinic. The fertilized egg then moves to the uterus, or womb, where it can attach to the uterine lining and develop into a fetus.
During ovulation, the walls of the uterus also thicken to prepare for a fertilized egg. But if the egg is not fertilized, the uterine lining is shaken off about two weeks later, causing menstrual flow to begin. But simply her menstruation does not always indicate that a woman is ovulating.
“The most misunderstood thing about ovulation is the idea that when you menstruate, it means you are ovulating; and this is indeed not the case at all,” says Dr. Mary Jane Minkin, a clinical professor of obstetrics, gynecology and reproduction. science at the Yale School of Medicine.
Many women have an ovulatory cycle – the buildup of the uterine wall – because they make estrogen. But when the buildup gets to a certain level, the lining just drops off, and a woman can bleed quite heavily, Minkin said. When a woman ovulates, she also makes the hormone progesterone, which results in a more controlled bleeding.
Timing / ovulation clues
Many people mistakenly believe that ovulation always occurs exactly 14 days after a woman’s last menstrual period. But the timing of ovulation differs for each woman and depends on the length of her menstrual cycle.
If a woman typically has 28-day menstrual cycles, she usually ovulates between days 13 to 15; If her cycle varies between 27 and 34 days, ovulation usually occurs between days 13 and 20, according to The American Society for Reproductive Medicine.
“Most women have no idea when they are ovulating,” said Dr. Christina Ramirez, an obstetrician and gynecologist in Garden City, New York, said.
In addition to timing on a calendar, a woman may have other clues that she is ovulating. Her body may have one of the following three signs:
1. Change in vaginal secretions.
A few days before a woman ovulates, her cervix, which is the lower part of the uterus, produces a type of mucus that is thin, clear, smooth and stretchy. This change in cervical mucus occurs when ovulation approaches and her ovaries prepare to release an ovum. The day after ovulation occurs, cervical mucus undergoes another change and it becomes thicker and cloudy.
2. Change in basal body temperature.
Keeping track of a woman’s basal body temperature, taken in the morning before getting out of bed, for two to three menstrual cycles can help predict when she’s fertile. Shortly after ovulation, many women show a slight increase (about 1 degree F) in early morning body temperature. A woman is most fertile during the 2 to 3 days before her temperature rises, according to the Mayo Clinic.
3. Increase in luteinizing hormone.
About 24 to 36 hours before a woman ovulates, her levels of luteinizing hormone increase. An increase in luteinizing hormone is a signal for the ovary to release an egg. This hormone increase can be detected by using an ovulation predictor set, which can test a sample of urine in the days before ovulation. When an increase in luteinizing hormones is detected, the test will show a positive result.
A woman is fertile – able to conceive – only during a certain part of her monthly cycle. The “fertile window” extends over a period of 6 days, the 5 days before ovulation and the day a woman ovulates, according to The American Society for Reproductive Medicine. Studies suggest that intercourse is most likely to lead to a pregnancy when it occurs in the three days leading up to the day of ovulation.
Home ovulation test
If a woman gets her period monthly but does not get pregnant, it may be because she is not ovulating. An ovulation predictor set can be useful to see if a woman is ovulating.
This kit, which is sold over-the-counter in drug stores, can test a woman’s urine to determine if she is experiencing an increase in luteinizing hormone, which usually occurs about 24 to 36 hours before ovulation, according to the Mayo Clinic .
A woman may want to start using the kit about 10 days after the start of her last period, the March of Dimes recommends.
“And if the test shows that ovulation is not happening, it’s a good time to go see your gynecologist: because getting women to ovulate is often pretty straightforward,” Minkin said. When ovulation is irregular or does not occur, doctors can try to induce the process by prescribing medication to stimulate a woman’s ovaries to release an ovum.
There are many reasons why a woman may have ovulation problems. Some women, for example, have had fallopian tubes blocked due to pelvic inflammatory disease, endometriosis, or surgery for an ectopic pregnancy, according to theU.S. Department of Health and Human Services.
An abnormal level of hormones can cause ovulation to be irregular or not occur at all, according to The American College of Obstetricians and Gynecologists. For example, polycystic ovary syndrome (PCOS), is a condition in which levels of certain hormones are abnormal and a woman does not get her period or it is irregular. Thyroid problems can also make the ovaries less likely to release an egg.
A woman who is underweight with a body mass index (BMI) of 18.5 or less may have irregular menstrual cycles and it may also cause ovulation to stop, according to the American Society for Reproductive Medicine. On the opposite end of the weight spectrum, obesity can also lead to irregular periods and irregular ovulation.
In addition, the timing of ovulation can be influenced by factors, such as stress and excessive exercise. Emotional or physical stress can delay ovulation or prevent a woman from ovulating. Getting too much intense physical activity can also inhibit ovulation, according to the Mayo Clinic.
Problems with ovulation are just one possible cause of infertility, which according to the CDC affects about 12 percent of women in the United States between the ages of 15 and 44.
Additional reporting by Alina Bradford, Live Science contributor.