fOLLICULar monitoring USG in sub fertility

All but obviously simple cysts should be treated with caution as ovarian malignancy may occur in young women. Therapeutic stimulation of the ovaries should not be performed until complex ovarian cysts have resolved, either naturally or surgically.

The baseline ultrasound scan also permits inspection of the other pelvic structures and might reveal the presence of the dorsal, fibroids; -sub mucus fibroids are of particular importance- or even an elusive intrauterine contraceptive device, which on removal should cure the patient's subfertility. A patient with hydrosalpinges visible on ultrasound should be counselled to consider salpingectomy to improve the outcome of IVF.

The resolution of transvaginal and transabdominal scans is 2-3 mm and 3-5 mm, respectively, so small follicles can be visualised easily as echo –free structures that are usually towards the periphery of the more echogenic ovarian tissue. The internal diameter of the follicle should be measured in three planes and the mean value should be calculated... In one study, the intra-observer standard deviation of transabdmi­nal follicular measurement was reported to be 0.6 mm and the interobserver standard deviation 1.2 mm, irrespective of the follicular diameter [38]. The 95% confidence limits for any particular measurement would therefore be ±2.4 mm. One would expect transvaginal measurements to confer greater precision. In natural cycles, therefore, the small follicles can generally be visualised approximately 10 days before the day of ovulation (day 4). By day 5, there is usually a dominant follicle that then grows at a rate of approximately 2-3 mm daily until the day of ovulation. For illustration of ultrasound scans of follicular growth.

Plasma oestradiol concentrations correlate quite well with follicular diameter in natural cycles but not in superovulated cycles, when not only is there great variation but also differential effects of the different drug regimens that may be used. The increase in circulating oestrogen levels results in an increase in the overall uterine size and a thicken­ing of the endometrium, thereby serving as a useful bioassay for oestrogen production.

It may be helpful to perform an ultrasound scan in the mid-luteal phase in both natural and stimulated cycles for IVF. The corpus luteum may have various appearances, being either ovoid or irregular in outline with either a cystic, echo-free interior or it may have a hazy, echodense appearance because of the presence of cellular debris and blood. The combination of a corpus luteum seen on ultrasound and an elevated serum progesterone concentration provides the best possible evidence of ovulation, although only a pregnancy will confirm that an oocyte was released from the follicle. Occasionally, there is no follicular rupture and a cystic structure persists in the luteal phase of the cycle associated with an elevated serum progesterone con­centration. This process is referred to as luteinised unruptured follicle (LUF). There is some debate about the incidence of the LUF syndrome. It occurs in less than 5% of cycles of patients undergoing ovulation induction therapy, and it does not tend to be a recurrent phenomenon.

Endometrial Assessment

Endometrial changes can be seen clearly using pelvic ultrasound (Figures 5.19 and 5.20). In the early follicular phase, when the endometrium is thin, there is a single hypoechogenic line produced by the opposed walls of the endometrial cavity. In the periovulatory phase, the oestrogenised endometrium takes on a characteristic triple line appearance (see Figure 7.24). In the luteal phase, the functional layer becomes hyperechogenic because of stromal oedema. The endometrial thickness in the early follicular phase is 4-6 mm, by the time of ovulation, it is approximately 8-10 mm and in the mid-luteal phase it may reach 4 mm. It has been suggested that there is a reduced chance of pregnancy if the triple line appearance is absent or if the pre­ovulatory endometrial thickness is less than 7 mm.

Doppler Ultrasound in Assisted Conception

The combination of transvaginal ultrasound with colour Doppler measurements can provide a detailed picture of follicular events around the time of ovulation, and it allows assessment of the uterine blood flow to predict endometrial receptivity. The precise uterine requirements for successful implantation have yet to be fully eluci­dated. The probability of a pregnancy occurring during assisted conception procedures depends on embryo quality and uterine receptivity. Methods to improve our ability to assess endometrial receptivity for implantation might help prevent the transfer of precious pre-embryos in cycles that are virtually doomed to failure. The embryos could then be frozen and transferred later, in a cycle that is judged to be optimal for implantation, perhaps after hormonal manipulation of the endometrial response. Until recently, the only way to assess endometrial receptivity was by endometrial biopsy. Doppler ultrasound has been suggested as a valuable, non-invasive method that provides an instantaneous picture of uterine blood flow.

Blood flow through the uterine and ovarian arteries

Blood flow through the uterine and ovarian arteries has been extensively investigated in spontaneous and stimulated cycles [44]. Doppler studies of the ovarian circulation are still at the research stage. It was reported in one study of natural cycles that resistance to arterial flow was lower on the side bearing the dominant follicle. In gonadotropin-stimulated cycles, it was reported that ovarian impedance was inversely proportional to the number of follicles greater than 15 mm in diameter. It also has been reported that, in IVF cycles, there was lower ovarian impedance 3 days after embryo transfer in those patients who conceived compared with those who did not. In practice, blood flow studies tend still to be performed only in centres with a research interest and have not gained widespread use.