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Ovulation Detection
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Ovulation is a phase in the menstrual cycle where a mature ovarian follicle ruptures and discharges an ovum (egg). Ovulation is triggered by a surge of luteinizing hormone (LH) in the woman’s blood, and occurs approximately 36 hours after the start of this LH surge. The ovulatory phase spans the period of hormonal elevation in the menstrual cycle. The process requires a maximum of thirty-six hours to complete. The average time of ovulation is the fourteenth day of an average length (twenty-eight day) menstrual cycle. It is normal for the day of ovulation to vary from the average, with ovulation anywhere between the tenth and nineteenth day being common. The few days near ovulation constitute the fertile phase. |
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Pregnancy |
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The ovulated egg moves toward the uterus through one of the fallopian tubes. For normal conception to occur, the man’s sperm must fertilize the egg (that is, it should attach to and penetrate the egg). This happens when the man ejaculates his semen, the fluid containing the sperm, into the woman’s vagina near the time of ovulation. 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 remains in the fallopian tube for a few days and then travels to the uterus and implants in the endometrium (lining of the uterus). It grows and matures in the uterus and, if all goes well, a child is born approximately nine months later.
If the egg is fertilized and implants in the uterine lining, 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. |
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Detecting Ovulation |
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Ovulation is one of the key factors in fertility. It is the most fertile phase in the menstrual cycle. Pinpointing the ovulation phase can be the first step in planning to conceive, especially for those who have trouble conceiving. A variety of problems can prevent or disrupt ovulation and result in infertility. If tests indicate that a woman is not ovulating, or that she has irregular cycles, treatments are available to correct the problem and increase the chances of a successful pregnancy. So, it is often necessary to determine whether or not a woman is ovulating. As ovulation approaches, a woman’s cervical mucus becomes more abundant, thin, slippery, and stretchy. This is an inexpensive, natural way to help identify a woman’s most fertile days. There are several other ways to detect ovulation, including urine test kits to measure LH levels, transvaginal ultrasound, endometrial biopsy, blood tests to measure hormone levels, and the basal body temperature (BBT) chart. |
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Urine Test Kits to Measure Luteininzing Hormone (LH) Levels |
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Ovulation Prediction Kits (OPKs) are available at chemists, supermarkets, and even online shopping sites. They use test strips to detect changes in the level of luteinizing hormone (LH) in urine. Ovulation usually takes place within 12 to 36 hours after the LH surge occurs. For women with 28-day cycles, ovulation usually occurs on days 13 to 15. Urine testing usually begins two days prior to the expected day of ovulation. 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 to 34 days, ovulation usually occurs between days 13 to 20. Therefore, testing should begin on day 11 and continue until ovulation is indicated or through day 20. There is an 80% chance of detecting ovulation with five days of testing, and a 95% chance with 10 days of testing. During any cycle, one can suspend the test as soon as ovulation is detected. Though occasionally ovulation might not occur in a particular cycle, failure to detect ovulation in two or more consecutive cycles is an indication of an ovulatory problem. |
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Transvaginal Ultrasound |
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A transvaginal ultrasound, also called transvaginal sonogram (TVS), is an ultrasound that uses an internal probe, or transducer, that enters the vaginal cavity. It can also be done with an external probe placed on the abdomen. Ultrasound uses sound waves to produce an image on a monitor screen. The ultrasound scan is performed to evaluate the number and size of the follicles. The follicle is thin-walled and filled with fluid before ovulation. As the egg inside the follicle develops, the follicle increases in size. The identification of a dominant follicle (which will be approximately 1.8 to 2.5 cm in diameter) indicates that ovulation is imminent. If a second ultrasound scan the next day reveals that the same follicle has returned to a smaller size, ovulation has occurred. Effective ultrasound can be integral to predicting ovulation and timing intercourse or insemination. For women undergoing fertility treatments, this test is done on different days (serial transvaginal ultrasounds) during menses in order to measure and monitor each follicle. |
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Endometrial Biopsy |
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An endometrial biopsy involves examining a tissue sample from the uterine lining under a microscope. Samples may be obtained in several ways that include scraping the uterus or using a suction device. If ovulation has occurred, the sample of tissue is likely to show the effects of Progesterone, a natural ovarian hormone that helps prepare the uterine lining to receive and support a fertilized egg. This test is performed just before menstruation is expected to begin. The precise day menstruation begins after the biopsy is crucial for interpreting the biopsy result. Maintaining a BBT chart and/or using an ovulation prediction test kit may be helpful in determining the best day to perform an endometrial biopsy and in interpreting the result. Endometrial biopsy is an invasive procedure and may be uncomfortable; it is usually reserved until other ovulation tests have been inconclusive. |
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Blood Tests to Measure Hormone Levels |
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Blood tests are one of the first tests conducted while medically assessing the factors that may be affecting your ability to get pregnant. Blood tests are an important diagnostic tool in helping to establish the best path for you in getting pregnant. Blood tests measure the levels of hormones like progesterone, LH, and estrogen in your body. The results of a blood test will indicate whether any imbalances in hormones may be negatively affecting your chances of getting pregnant. |
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 Elevated progesterone levels in the blood indicate ovulation. A blood test to measure progesterone can be performed about one week before the anticipated onset of the next menstrual period.
LH levels can be measured to predict when the follicle is mature and ready for ovulation. The LH surge occurs just before 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.
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Basal Body Temperature (BBT) Chart |
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Basal Body Temperature (BBT) is the body’s core temperature. It is the body temperature measured immediately after awakening and before any physical activity has been undertaken. In women, ovulation causes an increase of one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius) in basal body temperature (BBT). The production of progesterone during ovulation is the reason behind the temperature rise. 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. An increased body temperature for several days indicates ovulation has occurred. BBT charts can only confirm whether or not ovulation has occurred; they cannot predict when ovulation may occur.
Fertility experts suggest that the combined approach of charting basal body temperature and checking the change in volume and texture of the cervical mucus will give you a clear picture of your menstrual cycle, so that you can predict ovulation more accurately. |
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