What is Ovulation?
Ovulation is the process that occurs when the ovary releases an egg cell (ovum) into the fallopian tube. A woman may fall pregnant at any time but is most fertile during the period of ovulation. This usually occurs 12 to 16 days before the start of menstruation (monthly periods). In a woman with a regular cycle of 28 days, ovulation is likely to occur around the 14th day of the cycle.
For women who are actively trying to fall pregnant, it is important to ascertain when ovulation is taking place. The most accurate method to estimate the period of ovulation is via urine or blood tests although saliva home predictor kits, identifying the signs and symptoms associated with ovulation and an ovulation schedule tool (calculator/calender) may also prove useful. For couples who are experiencing difficulty with conceiving, frequent intercourse during the period of ovulation is advisable. If ovulation does not occur (anovulation), then fertility treatments may have to be considered.
Hormonal Changes during Ovulation
Certain hormonal changes occur in a woman’s body around the time of ovulation which give rise to the signs and symptoms associated with ovulation and which form the basis of the tests which predict or confirm ovulation.
- The first part of the menstrual cycle, from the first day of the last menstrual period (LMP) till just before ovulation, is known as the follicular phase. In the beginning of the follicular phase the estrogen level in the body is low, which initiates the secretion of follicle stimulating hormone (FSH) by the pituitary gland. FSH causes maturation of follicles in the ovary, of which one follicle develops into the dominant follicle and releases a mature egg while the others disintegrate.
- Estrogen is secreted by the follicles, which stimulates the pituitary to produce luteinizing hormone (LH), causing an LH surge. This triggers the release of the egg from the follicle. Hence, an LH surge indicates that ovulation is about to occur. This is the ovulatory phase, beginning with the surge in luteinizing hormone till the release of the egg (ovulation), which usually occurs 16 to 32 hours after the LH surge. During the ovulatory phase, the estrogen level is at its highest and the progesterone level starts to increase.
- The last part of the menstrual cycle (from the day of ovulation till beginning of the next period) is known as the luteal phase. During this phase the corpus luteum (follicle from which the egg was released) produces the hormone progesterone, which is responsible for preparing the endometrium of the uterus for a possible pregnancy till the placenta takes over this function (if pregnancy occurs). If fertilization does not take place, the ovum disintegrates and the hormone levels decrease gradually till menstruation ensues once more.
Progesterone causes a mild rise in body temperature which remains elevated till the next menstrual period. Hence, noting a rise in basal body temperature or detecting an elevated progesterone level in the blood will indicate that ovulation has occurred.
What is Anovulation?
Anovulation is the medical term for the absence of ovulation. The ovary releases a mature egg cell into the fallopian tube during the menstrual cycle and this process is known as ovulation. It can occur approximately 14 to 16 days before the start of menstruation (refer to Ovulation Schedule). In anovulation, this process does not occur.
The ovary may not release a mature egg cell for a number of reasons including ovarian disorders, menopause or perimenopause, pregnancy, hormone contraceptives, drugs or even severe stress, exercise and starvation (including strict dieting). Other chronic conditions, even those that are not gynecological in origin, may result in anovulation.
Anovulation is one of the main reasons for infertility in women. If ovulation does not occur during the course of the menstrual cycle then this is known as an anovulatory cycle. Anovulation should not be confused with amenorrhea which is the absence of menses. In an anovulatory cycle, normal menstruation will occur in most instances. If there is no ovulation and no period (menses), then this is known as anovulatory amenorrhea. Refer to Primary and Secondary Amenorrhea for more information on absent menses.
The absence of ovulation may occur many times in a woman’s fertile years but this is occasional and does not persist. In young menstruating girls or older women approaching menopause, anovulation is more likely although normal menstruation is occurring on a regular basis. Ovulation is not always detectable without medical investigation. A light vaginal discharge or lower abdominal pain or discomfort may indicate ovulation but this is not always present. Ovulation is best assessed by a female hormone screen, which is a blood test to measure changes in the female hormones during the menstrual cycle.
Signs and Symptoms of Ovulation
The signs and symptoms of ovulation must be looked for carefully as they are not always obvious.
- Basal body temperature (BBT) – there is usually a small rise in body temperature (usually 0.4 – 0.6 F) once ovulation has taken place. Recording the BBT (taken either by means of a special BBT thermometer or a digital thermometer) every day before getting up from bed for a few cycles will give an idea about the ovulation time by noting the temperature rise in each cycle.
- Changes in cervical mucus – normal cervical mucus is cloudy and sticky, or may be altogether absent in some women. Just before the time of ovulation the consistency of the cervical mucus may change and a copious amount of clear, slippery secretion, resembling raw egg-white may be seen.
- Mittelschmerz (mid-cycle pain) – some women get abdominal cramping or pain every month around the time of ovulation. They are usually more severe on one side of the abdomen and may last from a few minutes to several hours.
Some ovulation tests may be done at home, such as :
- Ovulation predictor kits (OPK) – the LH surge can be tested at home by means of ovulation kits which measure the hormone level in the urine. Passing urine on a test stick or dipping a test strip in collected urine, for a few days around the expected date of ovulation and noting the color change will indicate an LH surge. An LH surge indicates that ovulation is about to occur and is the time when there is maximum chance of getting pregnant.
- Saliva ferning – some ovulation predictor kits test for rising estrogen levels just prior to ovulation. The saliva-based OPK contains a pocket-sized portable microscope. The saliva is smeared on a slide and the dried saliva is examined with the microscope to look for the ferning pattern caused by estrogen, which will indicate that ovulation is about to occur. Although easier to use than the urine-based LH tests, the saliva ferning tests are not always accurate.
- Ovulation calculator and calendar – while not very helpful in women with irregular cycles, an approximate idea about the ovulation date can be obtained by putting the menstrual cycle dates into an ovulation calculator or calendar. Refer to the Ovulation Schedule online calculator for more information.
Ovulation tests that may be done at the doctor’s office :
- Blood test for progesterone – progesterone level varies throughout the menstrual cycle. An elevated serum progesterone level will indicate that ovulation has taken place.
- Ultrasound of the ovaries – high-frequency sound waves are used to scan the ovaries to determine accurately when an egg matures and ovulation takes place. Daily scans are done to visualize the growing follicle and watch for ovulation.
- Endometrial biopsy – a small portion of the endometrium is removed, stained and examined under the microscope. This test is done about a week before the expected period (7 days after ovulation) to look for secretory changes in the endometrium caused by progesterone. However, it is not a very reliable test for ovulation and is not often done.
Article reviewed by Dr. Greg. Last updated on September 9, 2012