As the follicle undergoes development, blood estradiol levels increase and peak just before ovulation—these can be measured with simple blood tests. Elevated progesterone levels in the blood usually are associated with ovulation. A blood test to measure progesterone can be performed about one week before the anticipated onset of the next menstrual period or one week after 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 usually done with a probe inserted into the vagina. 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. A medication that causes ovulation (hCG) can be administered to allow timing of intercourse.
Progesterone, a hormone released by the ovaries, helps prepare the endometrium, the lining of the uterus, to receive an embryo. An endometrial biopsy is occasionally used to 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.
For couples who are trying to conceive a baby, the key to success is knowing when a woman is most fertile during her monthly menstrual cycle. Most of the methods do not require any special equipment and can be done at home by the couple. Others require simple, low-cost equipment. Blood testing, ultrasound, and endometrial biopsy require medical intervention and are usually used for infertility evaluation or treatment.