Follicular development: lessons learned from human in vitro fertilization.

In vitro fertilization has offered new insights into our understanding of ovulation induction, folliculogenesis, and luteal phase events. This new information is provided by the ability to precisely study these cycles in a frequent and sequential fashion through the use of peripheral blood markers, ultrasound evaluation, and follicular fluid constituents and cell culture techniques, as well as direct observation of the oocyte, fertilization, and cleavage. In these stimulated cycles the follicular phase serum estradiol levels in conjunction with ultrasound were evaluated; a poor correlation was shown between follicle size and number and estrogen production. This distinct dyssynchrony suggests the recruitment of a number of cohorts of follicles in each stimulated cycle. From the biochemical markers in follicular fluid, cyclic adenosine monophosphate has a distinct predictive value in regard to pregnancy in in vitro fertilization-embryo transfer cycles. In the luteal phase, the mass effect of aspiration of great numbers of granulosa cells, the effect of supplemental progesterone, and the influence of high follicular phase estradiol levels remain controversial and, therefore, a less clear cut pattern emerges. Variations in the protocol have not greatly improved the major problems of folliculogenesis associated with ovulation induction and an in vitro fertilization-embryo transfer program, that is, follicular asynchrony and luteal phase deficiency.