How should poor embryo quality trends be investigated?

[Verified against the Vienna Consensus 2017] Work down the indicator sequence in order, because a deficit at any stage propagates and the first abnormal point localises the problem. 1. Reference indicators. These relate to oocytes entering the laboratory and proxy the response to ovarian stimulation. If the cohort arriving has changed, the laboratory is not the cause. 2. Fertilisation. Normal fertilisation ≥60% competency, polyspermy <6%, 1PN <5% IVF and <3% ICSI, failed fertilisation <5%. 3. Cleavage. Competency >95%, benchmark >99%. Note the cohort effect — at least one non-cleaved embryo predicts reduced quality across the remaining embryos. 4. Development rate. Day 2 ≥50% competency, Day 3 ≥45%. 5. Blastulation. ≥40% competency, ≥60% benchmark on Day 5. On grading-based indicators, the consensus is notably cautious and this is worth heeding. Embryo fragmentation rate is described as subjective and difficult to evaluate — one must distinguish a cell from a fragment and then estimate proportions. Survey competence values ranged from 20% to 90%. Grading systems are described as not robust, usable as internal quality assessment parameters rather than as comparators. Its conclusion is explicit: cleavage rate and embryo development rate are extremely important indicators, while early cleavage rate, rate of good quality embryos, and embryo fragmentation rate are less important as quality indicators. So a trend detected on subjective grading alone warrants confirmation against objective stage-based indicators before an investigation is launched. Practicalities: monthly review where caseload allows, otherwise a predetermined case number with 30 as a starting guide. Respond promptly to unexpected fluctuations rather than waiting for the next scheduled review.