Once the patient and doctor have produced eggs and sperm it is the laboratory’s job to create and grow healthy embryos. Thereafter, the doctor transfers those embryos into the woman’s uterus.
The clinic and doctor are interdependent. If the doctor’s protocol is unable to produce enough healthy eggs and sperm, or the laboratory enough healthy embryos, the cycle will end in failure.
In our minds, the laboratory has four key, discrete tasks to provide the doctor with healthy embryos to transfer. The laboratory needs to fertilize as many eggs as possible, cultivate the resulting embryos to a healthy state, be able to biopsy the healthiest embryos for genetic testing (if requested) and then freeze/thaw either eggs or embryos for future use. Each step is crucial, and there is often no agreed-upon ‘best practice’ to execute any step, but thankfully each discrete task can be measured and laboratories can be compared (which we'll cover in the next chapter).
We think of laboratories as elaborate kitchens: they are given ingredients (sperm and eggs) and must deliver a satisfying meal (healthy embryos). Like in the kitchen, the laboratory has chefs (embryologists), recipes (processes), pots & pans (culture media) and ovens (incubators). When one facet breaks down, results suffer.