Single embryo collection for Day 15 embryos was done using standard embryo flushing technique (Berg et al., 2010) using the same flushing medium and volumes as Day 7 recoveries. The ipsilateral uterine horn was flushed first, and flushing terminated when an intact elongation stage embryo was visually detected during the flushing procedure. The contralateral horn was only flushed if an embryo was not detected or an embryo fragment was recovered. Each uterine flushing was reduced by filtering the contents through a cup filter to approximately 20 mL. This was then transferred to a 90-mm Petri dish and searched as described for Day 7. The embryo was removed and immediately transferred into a 30-mL Petri dish containing EMCARE Holding solution. The length of the embryo was measured and was classified by trophectoderm (TE) length and morphology: spherical, ovoid, elongating (2–10 mm), tubular (10–30 mm), or filamentous (>30 mm). In the case of several TE fragments being found, the length of each fragment was measured and the lengths summed. The embryo was examined for the embryo disc (ED). If the ED was not located, the uterine flushing samples were re-examined for a detached ED. Each ED was photographed after microdissection of the ED from the TE.