A proper evaluation of the stimulation process includes both functional (i.e., hormonal measures) and morphological (i.e., ultrasound visualization) indices. The combined evaluation should identify a comfort zone between inadequate and excessive stimulation. Zone parameters are assuredly different for mono- or paucifollicular (classic) stimulations on the one hand, and multifollicular (for IVF) stimulations on the other.
5.1 Hormonal (Functional) Monitoring
The only essential hormonal parameter is the rapid plasma estradiol assay, but the evaluation process may be strengthened by addition of LH and/or progesterone measures.
Estradiol assumes the role of lead indicator because its level in blood reflects secretory activity of the dominant ovarian follicle coupled with that of numerous smaller follicles that have developed directly in response to the injected gonadotropins. For this reason pre-ovulatory estradiol is normally higher in stimulated cycles than in the spontaneous cycle. In the natural cycle, the dominant follicle releases estradiol in regularly increasing amounts from the sixth day CD until the pre-ovulatory peak, usually in the range of 125–250 pg/ml.
Measuring progesterone concomitantly with estradiol is a valuable safeguard because it represents another marker of the stimulation quality. However, levels should remain under 1 ng/ml throughout the stimulation process and readings that exceed 1 ng/ml would likely suggest one of the following:
· An unnoticed ovulation that occurred between two monitoring controls
· An abnormally developing stimulation, despite the presence of satisfactory estradiol and ultrasound parameters
· An inappropriately early follicular luteinization caused by erratic surges of endogenous pituitary LH
· The release of progesterone into blood as a result of FSH-promoted secretion from granulosa cells
During a normal follicular phase, progesterone originates in the theca interna and is converted to androgens for transport to granulosa cells where the production of estradiol is completed. In case of a relative lack of LH, more of the progesterone production may enter the blood instead of being moved along the steroidogenic pathways. An inappropriate increase of blood progesterone results in a thickened cervical mucus and an abnormally matured uterine endometrium that becomes visible on ultrasound. The stimulation cycle should be stopped when this occurs, although the treatment protocol should not necessarily be modified upon the initial occurrence. However, a repeated rise of plasma progesterone during a second consecutive treatment cycle should lead to consideration of protocol modification, or possibly to changing the gonadotropin itself. A progesterone level in excess of 5 ng/ml in the first monitoring sample might be a sign of an early pregnancy. Even if the patient believes she had a normal menses, a pregnancy test would be indicated.
5.1.3 Luteinizing Hormone
A serum LH assay is mandatory when an intra-uterine insemination is planned, but LH measures are also useful for a simple stimulation cycle intended for a single intercourse, in order to know if a spontaneous ovulatory process might have begun prior to hCG administration, a sign of optimal follicular maturity, or if it is the hCG administration that will trigger the ovulation:
An LH rise together with a concomitant progesterone rise suggests that a spontaneous ovulatory process has started within the previous 12–24 h, and that an ovulation will occur on the following day. It will no longer be possible to block this spontaneous event by means of a GnRH antagonist.
An LH rise in excess of twice its initial level, but without a progesterone elevation, is an early sign of a spontaneous ovulation that will likely occur 2 days hence; this is similar to the timing that follows an hCG administration. In this situation the spontaneous gonadotropin surge may still be arrested, or at least delayed, if necessary, by using a GnRH antagonist.
5.2 Ultrasound (Morphologic) Monitoring
Ultrasonic imagery for the purpose of monitoring ovulation is best performed though the endo-vaginal route because it places the ultrasound probe in the closest position relative to the pelvic organs being examined. Typical 2D imagery is sufficient to visualize the numbers of growing follicles as well as their shape, location, growth rate, and echogenicity. The images may also help clarify reasons why similar estradiol levels can occur with different types of follicular cohorts. The imagery should also help grade the thickness and echogenicity of the uterine mucosa, as well as the extent of cervical mucus secretion.
5.2.1 Ovarian Follicles
Ovarian follicles appear as transonic structures within the ovary. The mean diameter of a follicle is estimated by the average of two perpendicular diameters, with the calipers placed in contact with the internal follicular wall .
In a normal, spontaneous cycle, the selected follicle appears on CD 6 with a diameter of 10 mm, then it expands at a daily rate of 1–2 mm until reaching 15 mm diameter on CD 10. Expansion continues at 2.5 mm daily until ovulation, and may even accelerate during the final hours. A mature follicle typically measures 20–23 mm just prior to rupture .
Endometrial appearance and thickness can vary considerably throughout a spontaneous menstrual cycle and also during ovulation stimulation. The thickness of the endometrial mucosa should be measured close to the uterine fundus.
Beginning at the end of menses in a natural menstrual cycle, the follicular phase endometrium grows at a rate of about 1.5 mm daily, reaching a total thickness of 8–10 mm by CD 12. By this time the tissue has developed a 3-layered hypo-echogenic (“coffee bean”) appearance that changes after ovulation due to the effect of luteal progesterone that arrests further growth (Figs. 5.1 and 5.2) .
Preovulatory endometrium with three layers showing a characteristic “coffee bean” appearance (Image courtesy of P. Billet)
Post-ovulatory echogenic endometrium, with its vascularization visible through color energy Doppler (Image courtesy of P. Billet)
Recent advances in 3D ultrasound imagery that include automated follicle measurements would seem to be of value only in multifollicular stimulations, where the more numerous follicles have become pressed together. Distorted shapes can disrupt relations between the mean diameter and the true follicular volume . It remains to be seen whether 3D technology will really improve routine monitoring of classical stimulations.
In order to optimize chances of a good stimulation while avoiding excessive risks, a strategy of evaluating both hormonal and ultrasonic parameters is best. Some studies on exclusively hormonal, or exclusively sonographic, monitoring, or even totally blind stimulation have been published, but they were concerned only with COH, and represented simple feasibility exercises . In the event that the triggering criteria are not met, only the combination of dual hormonal and ultrasound measures provides a complete assessment of the three basic principles that underlie the FSH dosing strategy:
· When estradiol correlates correctly with the follicular diameter(s), the FSH dose should remain unchanged
· When estradiol rises in excess of the follicular growth, the FSH dose should be decreased
· When estradiol lags behind follicular growth, the FSH dosage should be increased, unless a relative LH insufficiency has been detected
Criteria for follicular maturity and ovulation triggering may vary according to the stimulation protocol, and additional discussion of posology will be undertaken in the succeeding chapters.
5.3 Monitoring After hCG Administration
Whereas follicular stimulation typically commands the clinician’s close attention, care can easily wane as soon as hCG is administered, almost as if a harmonious progress into the second part of the cycle were obvious. The quality of the luteal gland is of course strictly dependent upon an optimal follicular maturation, but the results of hormonal and ultrasonic monitoring during the pre-ovulatory period can only approximate actual follicle and oocyte maturity. It is well established that hCG administration with an immature or a post-mature follicle will lead to diminished chances for a successful pregnancy.
A normal luteal phase should demonstrate a clear shift of basal body temperature to a higher plateau lasting 12–14 days, and/or a plasma progesterone level in excess of 10 ng/ml on the seventh to ninth post-hCG day. On the other hand, complete follicular rupture does not always occur, and can be confirmed only by ultrasound imagery. Some studies have reported as much as a 40 % incidence of luteinized unruptured follicles (LUF) during stimulated cycles triggered with an hCG injection . Color energy Doppler is now sufficiently sensitive to differentiate the characteristic vascularity of a cystic corpus luteum from an unruptured follicle (Figs. 5.3, 5.4, and 5.5) .In the latter case, a second administration of hCG may provoke complete follicular rupture and restore chances for a successful pregnancy. An additional sonographic verification on the third post-hCG day is indicated even during the first attempt at a stimulation, and should become a standard procedure if several treated cycles of apparently good quality have not resulted in a pregnancy.
An intra-ovarian corpus luteum that is barely discernible with conventional ultrasound (a), but is clearly revealed through color energy Doppler (b) (Image courtesy of P. Billet)
An apparent unruptured follicle 72 h post-hCG seen by conventional ultrasound (a) but which is in fact a cystic corpus luteum revealed by color energy Doppler (b) (Image courtesy of B. Broussin)
A residual follicle 72 h post-hCG (a): color energy Doppler shows an unruptured follicle (b) (Image courtesy of P. Billet)
Duijkers IJ, Louwe LA, Braat DD, Klippig C (2004) One, two or three: how many directions are useful in transvaginal ultrasound measurement of ovarian follicles? Eur J Obstet Gynecol Reprod Biol 117:60–63PubMedCrossRef
Bakos O, Lundkvist O, Wide L, Bergh T (1994) Ultrasonographical and hormonal description of the normal ovulatory menstrual cycle. Acta Obstet Gynecol Scand 73:790–796PubMedCrossRef
Broussin B (2007) The clinical value of ultrasound for endometrial receptivity assessment in Assisted Reproductive Techniques (ART) procedures. Gynecol Obstet Fertil 35:570–615PubMedCrossRef
Salama S, Torre A, Paillusson B et al (2011) La monitorage de l’ovulation: passe, présent et perspectives. Gynecol Obstet Fertil 39:245–254PubMedCrossRef
Wiser A, Gonen O, Ghetler Y et al (2012) Monitoring stimulated cycles during in vitro fertilization treatment with ultrasound only – preliminary results. Gynecol Endocrinol 28:429–431PubMedCrossRef
Check JH, Nazari A, Barnea ER et al (1993) The efficiency of short-term gonadotropin releasing hormone agonists versus human chorionic gonadotropin to enable oocyte release in gonadotropin stimulated cycles. Hum Reprod 8:568–571PubMed
Miyazaki T, Tanaka M, Miyakoshi K et al (1998) Power and colour Doppler ultrasonography for the evaluation of the vasculature of the human corpus luteum. Hum Reprod 13:2836–2841PubMedCrossRef