Ovulation detection


Ovulation, the release of an egg from its follicle in one of the two ovaries is one of the most important factors in conceiving a child. In order for traditional conception to occur, the man must ejaculate his semen, the fluid containing the sperm, into the woman’s vagina near the time of ovulation. Once ovulated. the egg is picked up by one of the fallopian tubes and begins traveling toward the uterus (Figure 1). The man’s sperm must be capable of swimming through the vagina and cervical mucus, up the cervical canal into the uterus, and up into the fallopian tube, where it must attach to and penetrate the egg in order to fertilize it. The fertilized egg continues traveling to the uterus and implants in the endometrium. where it grows and matures. If all goes well. a child is born approximately nine months later.

Because a variety of problems can prevent or disrupt ovulation and result in infertility, it is often necessary to determine whether or not a woman is ovulating. There are several ways to detect ovulation, including the basal body temperature (BBT) chart, urine test kits to measure leuteinizing hormone (LH) levels, vaginal ultrasound, an endometrial biopsy, and blood tests to measure hormone levels. This booklet describes how ovulation occurs and methods of detecting ovulation.

The Menstrual Cycle and Ovulation

Ovulation is triggered by the LH .surge and occurs approximately 36 hours after the start of this surge. If the egg is fertilized and implants in the endometrium, a pregnancy is established. If a pregnancy is not established the endometrial lining that develops in preparation for pregnancy is shed as the menstrual flow.

Unlike men who continuously product new sperm throughout their lives, a woman is born with all of the eggs that she will ever have. These eggs remain in an immature state within the ovary until they either undergo ovulation or atresia (degeneration). Ovulation is a complex sequence of events involving hormones from the hypothalamus, pituitary, and thyroid glands, including gonadotropin releasing hormone (GnRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin, and thyroid hormone.
Figure 1 : The female reproductive tract. Solid arrows indicate path sperm must travel to reach the egg. Dotted arrow indicates path of egg. The fertilized egg continues traveling through the fallopian tube to the uterus.

The hormones released by the egg’s follicle in the ovary cause the endometrium to develop in anticipation of implantation. The coordination of this system is one of the most remarkable events in the body. resulting in the release of a mature egg at the exact time the cervical mucus is most receptive to sperm. Fertilization usually occurs in the fallopian tube 12 to 24 hours after ovulation. After this period of time, the egg loses its ability to be fertilized and begins to degenerate. If fertilized, the resulting embryo reaches
the uterus about three to four days later and begins to implant in the endometrium.

The menstrual cycle is divided into three phases: the follicular phase. mid-cycle. and the luteal phase. The follicular phase lasts 10 to 14 days, beginning with the onset of menstruation and lasting until the onset of the LH surge. During the follicular phase, the hormone FSH triggers the development of many follicles and encourages the egg in the dominant follicle to mature. The dominant follicle increases in size and secretes estrogen into the bloodstream. The increasing levels of estrogen cause the hypothalamus and pituitary to decrease the production of FSH, insuring the development of a single egg.

As the egg matures during the mid-cycle, estrogen levels rise. Triggering the pituitary gland to release a large amount of LH (the LH surge), which stimulates the release (ovulation) of the egg from its follicle in the ovary.

The LH surge usually occurs 34 to 36 hours prior to ovulation. It can be measured in either the blood or the urine. The luteal phase, which generally lasts about 14 days, begins after ovulation, when the empty follicle collapses and becomes known as the corpus luteum. The corpus luteum secretes large amounts of progesterone, the hormone responsible for the rise in basal body temperature characteristic of the luteal phase. Progesterone also induces specific changes in the endometrium that make it receptive for embryo implantation. The highest levels of progesterone occur about one week after ovulation and then decline if a pregnancy does not result. Declining progesterone levels allow break down of the endometrium, which results in menstruation. Abnormal progesterone secretion may be caused by poor follicular development, inadequate LH levels during the mid-cycle surge, or inadequate LH after ovulation.


Cycle Length

In most women aged 15 to 44, the average menstrual cycle length is 28 days. However, normal menstrual cycles may range from 21 to 35 days. The menstrual cycle starts on the first day of menstrual flow. Ovulation usually occurs between the 13th and 15th day of a 28-day cycle. Keeping track of menstrual cycle length can help determine the approximate time of ovulation.

Abdominal Pain

Mittelscchmerz refers to a pain on one side of the abdomen near the time of ovulation. Mittelschmerz discomfort may begin prior to actual ovulation and is generally caused by nerve fibers that stretch as the follicle matures. Pain experienced after ovulation is usually due to irritation of the body lining (peritoneum) by the small amount of fluid or blood that leaks into the pelvis after ovulation. This pain may last for one to two days.

Cervical Mucus Test (Billings Method)

Another indication of impending ovulation is an increase in cervical mucus discharged from the vagina and sometimes visible to the woman (Figure 2) This is due to the increasing estrogen secreted by the growing ovarian follicle. Early in the cycle, the cervix is closed and there is no mucus When mucus production begins, the early mucus is thick, cloudy, and sticky. As the cycle progresses, the mucus becomes abundant, slippery, clear and elastic conditions favorable to sperm passage. These changes begin about two or three days before ovulation. After ovulation. the mucus becomes thick again

Figure 2 : the cervical mucus test can provide information about ovulation

Basal Body Temperature (BBT) Chart

The basal body temperature chart helps to monitor the duration of the different phases of the menstrual cycle and can help determine if and when ovulation has occurred. During the follicular phase, the woman’s body temperature is relatively low. When progesterone production begins at ovulation. it produces a temperature rise with a minimum increase of 0.5 degrees Fahrenheit (Figure 3). An increased body temperature for several days indicates ovulation has occurred. BBT charts cannot predict when ovulation is going to occur: they only confirm that ovulation has occurred after the tact. The following are general instructions for keeping a basal body temperature chart:

1. The chart starts on the first day of menstrual flow. Record the date and place an “x” on the chart for each day of menstrual bleeding. 2. After your period is over, or on about the fifth day of bleeding, begin taking your temperature every morning before getting out of bed and before eating, drinking, or smoking. Record your temperature on the chart every day. noting any unusual circumstances such as insomnia, illness, or alcohol consumption. Also note on the chart each time you have sexual intercourse or have a test for infertility. When your next period begins, start a new chart.

Blood Tests

Elevated progesterone levels in the blood are usually associated with ovulation. A blood test to measure progesterone can be performed about one week before the anticipated onset of the next menstrual period. The LH surge occurs just before ovulation. LH levels in the blood or urine can be measured to predict when the follicle is mature and ready for ovulation. Estrogen is secreted by the growing follicle and rises rapidly prior to ovulation. If ovulation is being induced with fertility drugs, frequent estrogen level measurements may be needed to determine follicular growth. Common hormonal problems such as thyroid gland disorders or excessive secretion of the hormone prolactin can cause ovulatory disturbances. Levels of these hormones can also be measured by blood tests. In women with excess hair growth or acne, the physician may suggest measuring the male hormones {androgens). since increases in these hormones are associated with adrenal gland and ovarian disorders which can also prevent ovulation.


Follicular- growth can be measured with ultrasound, a technique which uses sound waves to produce an image on a monitor screen. This is a painless procedure that can be done using either a vaginal probe or an abdominal scanning device. Prior to ovulation. the follicle is thin-walled and filled with fluid. As the egg inside the follicle develops, the follicle increases in size. Ovulation generally occurs when the follicle measures about 1.8 to 2.5 centimeters. Ultrasound is especially useful for timing intercourse or insemination. In women taking fertility drugs, ultrasound may he performed on several different days during the menstrual cycle so that each follicle can be carefully measured and monitored.

Ovulation Prediction Kits

Several ovulation prediction tests are available at drug stores. These kits use paper dip sticks that show changes in the level of LH in the urine. Once the LH surge has occurred, ovulation usually takes place within 12 to 44 hours. Urine testing usually begins two days prior to the expected day of ovulation. For women with 28-day cycles, ovulation usually occurs on days 13 to 15. For women with irregular menstrual cycles, urine testing should be timed according to the earliest and latest possible dates of ovulation. If the cycle ranges between 27 and 34 days, ovulation usually occurs between days 13 and 20. Therefore, testing should begin on day 11 and continue until ovulation is indicated or through day 20. There is an 80 percent chance of detecting ovulation with five days of testing and a 95 percent chance with ten days of testing. Once ovulation is documented, it is no longer necessary to continue testing. Occasionally, ovulation may not occur in a particular cycle. If ovulation is not detected in two or more consecutive cycles, an ovulatory problem may be present.

The following are general guidelines for ovulation prediction tests that are based on detecting LH in the urine:

1. The manufacturer’s instructions should be followed precisely.
2. Urine that is very dilute (light) may not have an adequate concentration of LH for detection. Therefore, women should avoid food and liquids for two to four hours before obtaining urine for testing so as to have an adequately concentrated (dark) urine sample.
3. False positive results in urinary LH detection may occur if the woman is currently pregnant, has recently been pregnant, or is close to menopause. Fertility medications such as human menopausal gonadotropin (hMG). human chorionic gonadotropin (hCG). or clomiphene citrate may also cause inaccurate results. Women taking any of these drugs should consult their physician before using a urinary ovulation prediction test and ask the manufacturer about the medication’s effect on the test kit.

Endometrial Biopsy

Progesterone helps prepare the endometrium (lining of the uterus) to receive an embryo. An endometrial biopsy can determine if a woman has ovulated and if the endometrium has been adequately stimulated with progesterone. During this office procedure, a small amount of endometrial tissue from inside the uterine cavity is removed and examined under a microscope. This test is performed just before menstruation is expected to begin. In order to interpret the endometrial biopsy, the physician will need to know the day that menstruation begins after the biopsy. Maintaining a BBT chart and/or using an ovulation prediction test kit is generally helpful in determining the best day to perform an endometrial biopsy and also in interpreting the result.

If the degree of progesterone-induced changes in the endometrium is less than what is expected, a luteal phase defect may be diagnosed. A second biopsy may he needed to confirm this problem. Medication may be recommended to help correct the situation. Progesterone given either orally, vaginally, or by injection after ovulation may help to correct a luteal phase defect by exerting a direct effect on the endometrium. Clomiphene citrate, an ovulation inducing medication, may act indirectly on the endometrium by improving ovulation. It is not known which treatment is best for luteal phase detect.


Abnormal ovulation may appear in several ways. Menstrual cycles that are shorter than 21 days or longer than 35 days are often associated with anovulaiton. Lack of a menstrual period for three months or more is called oligomenorrhea. The complete absence of menstrual periods is referred to as amenorrhea.

Many hormonal systems work together to produce regular menstrual periods, and the hormones that make up these systems are often evaluated to determine the cause of ovulatory disorders. Therefore, in order to prescribe the appropriate therapy, physicians may require additional tests to determine why ovulation is not taking place.
Common conditions that may cause irregular ovulation or anovulation include disorders of the hypothalamus. Hypothalamic disorders are usually caused by subtle changes in the signal sent from the hypothalamus to the pituitary gland. This may result in changes in the secretion of FSH and LH and may cause ovulatory disturbances. Acute stress as well as rapid weight loss or weight gain can alter the function of the hypothalamus and pituitary glands and cause anovulation. An elevation of the pituitary hormone prolactin may also lead to absence of menstrual periods and anovulation.

Disturbances involving the thyroid gland can affect ovulation. Although less common, disorders of the adrenal gland may also be associated with anovulation. Blood tests are usually needed to confirm the diagnosis of these disorders.

Polycystic ovary syndrome (PCOS). a condition which is frequently associated with weight gain, excess hair growth on the face and body. And irregular menstrual periods, can cause irregular ovulation or anovulation. Women with PCOS frequently have an increased LH level relative to the FSH level, which can be detected by a blood test. Increased androgens are also frequently present. In most cases, medical therapy with fertility drugs is successful in restoring ovulation. A thorough evaluation, including hormonal studies and appropriate medical therapy, may be required if these disorders are suspected.


Clomiphene citrate, the most commonly prescribed ovulation drug. is an oral medication often used to regulate ovulation or to induce ovulation in women who are not ovulating or do not have normal menstrual cycles. Clomiphene citrate is also used to time ovulation for patients who plan to undergo insemination.

Human menopausal gonadotropins (hMG) are injectable medications that stimulate multiple follicle development. Physicians may prescribe these medications for patients who do not respond well to oral therapy such as clomiphene citrate.

Gonadotropin releasing hormone (GnRH), a hormone secreted by the hypothalamus which prompts the pituitary gland to release FSH and LH. Is released from the hypothalamus in small amounts approximately every hour or so. Synthetic GnRH can be administered by a pump to stimulate the pituitary to secrete LH and FSH. This medication is only useful for women who are anovulatory due to abnormalities in FSH and LH release.

GuRH analogs may be used as adjunctive therapy to enhance induction of ovulation with other drugs. These analogs are prescribed to women whose hormonal patterns interfere with normal follicular development or with the administration of hMG.