Supervising Ovulation Induction

Normal Folliculogenesis

Before reviewing the details  the parameters of follicular  growth studied  with 2D  ultrasound  imaging , it is  helpful  to summarize   normal folliculogenesis in order   to be able  to correlate   imaging   findings  with physiologic   expectations. Follicles   grow in two  stages the gonadotropin independent and gonadotropin dependent  stages. Primordial follicles   consist of an oocyte with a thin layer of granulosa and stromal   cells and cannot be  seen on ultrasound. By  The time follicles  develop  a fluid   antrum they are    ultrasonographically   identifiable  and they  have    reached the gonadotropin dependent stage  of the 3 month   maturation process. These  antral follicles  measure between 2 and 10 mm  and represent   the pool of  follicles  that may be  recruited  in the ensuing  follicular   phase . In a   natural  cyce one  is ultimately selected  for ovulation and that selection process occurs   during  the latter half  of the follicular   phase of the ovarian cycle   when the endogenous pituitary follicle  stimulating hormone level   is falling in response  to the increasing    ovarian   estradiol production. Falling FSH  promotes a selection process  in which each  of the follicular microenvironments   competes for  the diminishing FSH needed   to stimulate   granulosa   cells in the follicle   to produce   aromatase . Aromatase in turn   is necessary  to convert testosterone and   androstenedione produced in the peripheral theca   cells into   estradiol and estrone respectively . Failure   of this conversion   leads  to an elevated androgen to estrogen ratio which leads  to follicular   atresia. From this  cursory review of the  anatomy and physiology  of oocyte  maturation , it is easy to see how  ovulation inducing agents  that either indirectly  increase   endogenous FSH   or  directly   add FSH  to the system   diminish the completion between   the follicles  and permit the development of  multiple  dominat follicles .

Monitoring  Follicular  Maturation

Methods  for Monitoring

It is   difficult to predict  the optimal number of growing ovarian    follicles in an IVF cycle , since   there is   considerable   variation   in ovarian   response among   women undergoing   ovulation     induction   therapy. The ovarian  response    depends  on age ovarian reserve  how the hypothalamic  ovarian axis  is manipulated exogenously   FSH  done cause  of infertility ethnicity  etc.

Follicular   maturation in IVF   cycles can be   monitored  clinically in different ways , either  by

Serum   estradiol  value  alone

2D   ultrasound alone

3D   ultrasound alone

Serum   estradiol  and  ultrasound combined 

Supplemental  power Doppler   imaging

There  are   numerous   studies on the use of  these different methods  for monitoring   of an IVF  treatment cycle   includes  a combination of regular  ultrasonography   and serum  estradiol   concentrations  and has long  been    accepted  as the gold  standard. However  the need for estradiol monitoring   remains controversial  . Ultrasound    provides     more accurate     measurement    of follicle   number    and size   than can be   obtained by serum  estradiol  alone. Whether  serum estradiol  or ultrasound is superior to the other is  questionable , but  it has been shown that  ultrasound   imaging of follicular growth  and endometrial   thickness  is sufficient to  monitor  follicular   maturation .

Which    approach when to adjust   the gonadotropin   dose up or   down and how often      monitoring   should be  done is  dependent   on the individual clinician the experience   and the routine at each individual   clinic Some   monitoring  methods are very complex   whereas   other methods   are rather simple however   the outcomes of IVF  cycles seem to be the same regardless of the chosen method.