The vaginal probe ultrasound allows the physician to view the ovaries, uterus, and other internal organs. A probe is placed inside the vagina where it emits ultrasound waves that are "reflected" differently dependent upon the type of tissue. The image produced by ultrasound is similar to that of an x-ray; however, the ultrasound does not involve potentially harmful radiation.
Numerous ultrasound measurements are required during cycles where fertility medications (ovulation induction agents) are administered.
The ultrasound is used to monitor the size and number of follicles produced in the ovary. It is usual to check the resting ovary for cysts before the commencement of therapy with fertility medications (induction of ovulation or super ovulation). If significant cysts are present, the cycle should be abandoned.
As the process to stimulate egg production continues, ultrasound is invaluable in measuring the follicular diameter (the pocket of fluid in which the egg resides.). When the mean follicular diameter reaches 18-20 mm, ovulation may be triggered with an hCG injection. hCG mimics the body's release of LH.
Ultrasound also provides valuable information about the following aspects of the reproductive process:
- Thickness of the endometrial stripe (the lining of the uterus). Eight to 10 mm is optimal.
- The successful rupture of the follicle and the formation of a corpus luteum, which produces progesterone.
- The presence of fibroids and polyps within the uterus that may alter the blood supply to the endometrium and hence an implanting pregnancy.