While the maxim stated at the beginning of this chapter that only good quality oocytes can make good quality embryos is true, it is easily derailed and that we can make poor quality embryos from good quality oocytes using inappropriate conditions.

What defines a “good” embryo? There are as many embryo scoring and grading systems as there are IVF units, and some of the most commonly used criteria of fragmentation and overall morphology are currently being reexamined in the light of several observations, originally based on specific observation times and, more recently, the advent of time lapse recording systems [3]. Even with the most stringent scoring systems, the “best” embryos have only a 50 % chance of implantation. This suggests that the use of such systems is limited as to its efficacy. More recently, the term “on time, appropriate development,” as defined by the Alpha/ESHRE consensus, has proved to be at least as effective as the more complex methods. Again, time lapse measurements of early development are adding more precise information to appropriate development [11].

On time, appropriate development and the effect on implantation rates are illustrated in Fig. 36.2, where the same dataset used for Fig. 36.1 was used. It is quite clear from this graph that the embryos from the poorer prognosis groups develop at a slower rate, and these differences increase with extended culture.

The differences between the groups are further illustrated in Fig. 36.3, where the ratio of blastocysts forming on day 5 was greatest for the “good” prognosis groups (donor and first cycle patients) compared with the “poor” prognosis groups (advanced maternal age and RIF patients). The overall utilization rates (defined as the percent of zygotes that were either transferred or frozen) and implantation rates per embryos transferred fresh follow the same trends. The apparent decrease in miscarriage rates suggests that “good” prognosis embryos are less liable to fail in pregnancy maintenance.

Using the “on time, appropriate development” methods should now give us more quantitative methods to look at the effect of stimulation regimes on embryonic development. However, can we make the contention that if only “good” oocytes make “good” embryos, will the measurement of zygote syngamy be sufficient by itself to investigate differences in stimulation regimens?

There are three main areas of ovarian stimulation which can potentially affect the quality of oocytes and embryos. These are suppression of pituitary functions using GNRH agonists and antagonists, stimulation of follicular development with FSH, and the “trigger” used to initiate oocyte maturation and release. Various adjuvants have also been used to attempt to mediate all of these processes.