Initial infertility ultrasound investigations emphasized follicular rupture and corpus luteum formation. A method which we have developed and utilized for a three year period includes endometrial assessment and staging. We refer to ovarian ultrasound in fertility assessment as Ovulation Verification by Ultrasound Methods (O.V.U.M.). The O.V.U.M. approach utilizes three ultrasound parameters: 1) follicular change, 2) corpus luteum formation, and 3) development of secretory endometrium.
Follicular change can be classified into three categories: 1) rupture and complete collapse of a follicle, 2) rupture with partial collapse of the follicle, and 3) unruptured increasing in size with or without internal hemorrhage.
We have observed four "typical" patterns in corpus luteum appearance. A corpus luteum may appear as 1) a thick walled doughnut without fluid after rupture and complete follicular collapse, 2) a thick walled cyst after partial follicular collapse, 3) a thick or thin walled cyst smaller than the follicle with a few echoes representing hemorrhage, and 4) development after rupture and complete collapse of a smooth walled corpus luteum cyst which may approach or surpass the size of the original follicle. This last pattern may develop in a 48 hour time interval. Therefore daily imaging is required once the follicle attains a size of 1.5 to 2.0 cm.
The third parameter we have been assessing is that of endometrial changes related to follicular and corpus luteum function. We have developed criteria which can differentiate late proliferative endometrium from early and late secretory endometrium. Proliferative endometrium appears as a triple line in the uterine cavity; the central line representing the cavity itself and the two outer lines representing the endometrium. As the endometrium progresses to the late proliferative stage the two outer lines become thicker than the central line but do not achieve an echo density greater than the myometrium. Early secretory endometrium is present when the two outer lines become thicker and more echogenic than the center line and the myometrium. Definite secretory endometrium takes place when the two outer lines thicken to the point of obscuring the center line and appear much more echodense than the myometrium. Increasing accoustical enhancement posterior to the endometrium is also characteristic of secretory endometrium. The ability to differentiate proliferative and secretory endometrium has been confirmed by endometrial biopsies obtained on the same day as the ultrasound procedures. It is felt that the ability to monitor the hormonal response of the endometrium as it relates to pre-ovulatory follicular estrogen and post-ovulatory corpus luteum progesterone is very helpful in follicular assessment. The O.V.U.M. approach holds exciting potentials in not only the anatomical assessment of follicular development and ovulation, but the assessment of physiological function of follicles and corpus lutea as monitored by endometrial imaging. Direct verification of ovulation using the O.V.U.M. approach is now possible. Indirect methods such as serum progesterones, basal body temperature charting and endometrial biopsies can indicate ovulation when in fact follicular rupture has not occurred. This has now enabled the diagnosis of luteinized unruptured follicles.
Ten patients who have achieved pregnancy during the time of a complete ultrasound cycle demonstrated the three parameters in normal sequence. No pregnancies have been achieved when the parameters were out of sequence. The illustration below demonstrates the parameters in normal sequence during a pregnancy achievement cycle.
