There are a variety of tests to try and work out if a woman is releasing eggs (ovulating). Unfortunately there is not one test that can tell for sure if ovulation will or has happened.
- Ultrasound scan of the ovaries. This type of scan is called a follicle-tracking scan because it measures the bubble of fluid called the follicle in which the egg grows. Human eggs are microscopic and cannot be seen with the human eye. If a follicle is seen to be growing in size from one scan to the next, then it is likely to contain an egg. Once this follicle reaches 18-25mm in diameter then it usually will contain a mature egg. A scan in the next 24-48 hours will show that the follicle has ruptured and changed in appearance if ovulation has happened.
- Urine testing for ovulation hormone (LH). Once a mature egg is ready to ovulate the body usually releases a “surge” or large amount of LH hormone to cause ovulation to occur. This LH hormone can be easily detected in the urine using a commercially available urine ovulation kit.
- Basal body temperature monitoring. Once ovulation has happened the body temperature rises by 0.5 degrees Farenheit. Often a small dip in temperature is seen just before this rise. Both of these slight temperature changes can be detected with a sensitive thermometer, used to measure your morning resting temperature before you get out of bed (basal body temperature).
- Progesterone blood test. When ovulation takes place, levels of the hormone progesterone rise. The amount of hormone present can be detected in the blood. This rise can be found on a blood test that is done seven days before your period starts. If you have a 28-day menstrual cycle the test is performed on day 21. If your cycle is longer or shorter the day of the test will be altered. The doctor will calculate which is the correct day for you according to your menstrual cycle.
Most fertility clinics now advise ultrasound scanning or LH urine testing, as they have the advantage of picking up signs before the egg releases, at a time when sexual intercourse is recommended to maximise the chance of pregnancy. Both progesterone blood testing and basal body temperature testing only show signs after ovulation has already happened, at a time when sexual intercourse is less likely to result in a pregnancy.
Maximum pregnancy rates are actually seen when sexual intercourse takes place in the 24 hours before the egg releases. This ensures that sperm are ready and waiting for the egg inside the fallopian tube. The sperms are capable of living for several days inside the womb & tubes, however the egg probably lasts 12 hours at most. This is why the most up-to-date advice for timing sexual intercourse is to be sexually active in the 24 hours before ovulation.