Day 6 blastocyst

Some embryos reach the blastocyst stage on day six rather than day five. These are commonly frozen and used in a later cycle, and can result in healthy pregnancies, although on average day five blastocysts implant slightly more often. Slower development alone is not a reason to discard a good-quality embryo.

Also known as: day six blastocyst, slow blastocyst

Last reviewed: 8 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.