Study design
With the approval of the Ethics Committee of the Third Hospital of
Peking University (No. 2020-419-01), the clinical data of pregnant women
who underwent in vitro fertilization/intracytoplasmic sperm injection
(IVF/ICSI) and embryo transfer and delivered at the Third Hospital of
Peking University from January 2012 to February 2022 were collected. The
live birth cases were divided into three groups according to the embryo
transfer method: the fresh embryo transfer group, natural cycle
(NC)-frozen-thawed embryo transfer (FET) group, and hormone replacement
therapy (HRT)-FET group.
Inclusion criteria: gestational age ≥24 weeks, live birth, and single
pregnancy or single intrauterine foetal demise or reduction before 12
weeks.
Exclusion criteria: 1) ART with donor sperm , 2) conception after
preimplantation genetic diagnosis, 3) definite foetal malformation
before delivery, and 4) intrauterine foetal death or reduction after12
weeks.