Ovulation is the release of an egg from a woman’s ovary and is important for getting pregnant. Ovulation happens spontaneously about 36-40 hours after blood levels of a hormone luteinizing hormone (LH) rise which is called the LH surge.
Once released from the ovary, the egg is picked up by the fimbria of the fallopian tubes and travels down the fallopian tube where it can meet the sperm to fertilize and become an embryo.
Why is ovulation important?
For a couple who is trying for pregnancy, knowing when the female is about to ovulate can be helpful in planning when to have intercourse. Problem with ovulation (anovulation) is a common cause of infertility. If a woman is trying to find the reason for infertility, it is helpful to know whether she is ovulating and when the ovulation is happening.
Having regular menstrual periods between accompanied by menstrual cramps is a good indication of ovulation. There are several ways to test for ovulation: the basal body temperature (BBT) chart, urine test kits to measure LH levels, blood tests to measure levels of certain hormones and transvaginal ultrasound.
What tests are available to check for ovulation?
Blood tests to measure hormone levels
- Serum estradiol – Estradiol is produced by the follicle as it grows and blood levels go up quickly just before ovulation.
- LH – A rise in LH levels in the blood can predict when the follicle is mature and ready for ovulation. Because LH is released in pulses or short bursts, the LH surge is not always found by a single blood or urine test, so serial tests have to be done to predict ovulation.
- Progesterone – Increased progesterone levels in the blood a week before the menstrual period usually indicates ovulation has occurred but cannot predict the time when ovulation had happened.
Urine test kits to measure LH levels
These are home test kits just similar to pregnancy detection kits, available at drug stores which show changes in the level of LH in the woman’s urine. Urine testing for LH surge should begin at least 2 days before the expected day of ovulation and continue until the LH surge or through day 20.
For women with irregular periods, urine testing should be timed according to the earliest and latest possible dates one is expected to ovulate. Once it is detected in the urine, ovulation usually takes place within 12 to 24 hours.
There is about 80% chance of detecting ovulation with 5 days of testing, and 95% with 10 days of testing with the LH detection kits.
Once the surge is detected, it is no longer necessary to continue testing during that cycle. Occasionally, ovulation may not occur in a cycle despite the detection of an LH surge. If ovulation is not detected in 2 or more cycles in a row, there may be a problem with ovulation and the couple should meet an infertility specialist.
The egg develops within a part of the ovary called the follicle. As the egg gets ready to ovulate the follicle grows in size. Follicle growth can be measured with ultrasound. Before ovulation, the follicle is thin-walled and filled with fluid.
Ovulation generally happens when the follicle measures between 1.8 and 2.5 centimeters. For women having treatment for fertility, ultrasound may help time intercourse or insemination. In women taking fertility drugs, ultrasound may be done on several different days during the menstrual cycle to measure and monitor each follicle (follicular monitoring).
Basal body temperature (BBT) chart
Daily measurement of basal body temperature during the ovulatory period can help determine if ovulation has occurred.
However, BBT charting is only an estimate of ovulation timing and can confirm that ovulation has happened but will not predict when it might occur. Although not very helpful or accurate to time intercourse, it is an inexpensive, easy way to gather information at home.
Although determining whether ovulation is happening and when it is occurring might seem frustrating and time consuming, it is often an essential step toward achieving pregnancy.
If these tests indicate that the 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.