Transfers of fresh blastocysts and blastocysts cultured from thawed cleavage embryos are associated with fewer miscarriages.

The literature shows an inconsistent relationship between miscarriage and assisted reproduction treatment factors. This study assessed the association between miscarriage and transfer of fresh or thawed embryos at cleavage/blastocyst stages. A population study included 52,874 pregnancies following autologous cycles. The miscarriage rate was compared by groups of transferred embryos (fresh cleavage embryo, fresh blastocyst, thawed cleavage embryo, blastocyst from thawed cleavage embryo, thawed blastocyst), IVF/intracytoplasmic sperm injection procedures, number of embryos transferred and woman's demographics. The overall miscarriage rate was 18.7%. Women aged 35-39 years and ≥40 years had a 51% and 177% increased hazard of miscarriage, respectively, compared with women <35 years. Women with history of miscarriage had 1.22 times hazard of miscarriage compared with those without previous miscarriage. Singleton pregnancies following fresh double-embryo transfer had 1.43 times higher rate of miscarriage than fresh single-embryo transfer. Fresh blastocyst transfer was associated with 8% less hazard of miscarriage than fresh cleavage-embryo transfer. Compared with pregnancies following thawed cleavage-embryo transfers, thawed blastocyst transfers were at 14% higher hazard of miscarriage. This study suggests that a practice model that includes transferring blastocysts and freezing cleavage embryos in fresh cycles would result in better outcomes.