Frozen embryo transfer has gained popularity in the recent years compared to Fresh embryo transfers. Frozen embryo transfers are done predominantly in women who suffer from Polycystic ovaries with a view to reducing complications such as Ovarian Hyperstimulation.
Discussion on success rates between Fresh vs Frozen embryo transfers are debatable as there is no clear cut evidence of superiority of one over the other. Embryos transferred can be either day 3 (cleavage stage) or day 5 (Blastocysts stage). Blastocyst stage embryos have been left to develop a little longer than D3 embryos. This helps with natural selection and helps the embryologist with selecting embryos which are likely to implant. We will need to bear in mind that not all embryos will develop further from day 3 to day 5 to become blastocysts as they might stop growing, this risks the loss of embryos. Your doctor will be considering these factors before deciding on your embryo transfer.