Study design
The 9832 FET cycles were divided into three groups according to female
age: < 35, 35-39 and > 39 years, and two groups
depending on their post-thawed
culture period: short culture (2-3 h) group (S) and long culture (18-20
h) group (L). The long culture group divided into three groups depending
on the blastomere growth number: ≤ 2 group (blastomere growth number of
each transferred embryo was ≤ 2), one ≤ 2 and the other > 2
group (blastomere growth number of the two transferred embryos was that
one was ≤ 2 and the other was greater than > 2) and
> 2 group (blastomere growth number of each transferred
embryo was > 2).
Clinical outcomes included
implantation rate (IR), clinical
pregnancy rate (CPR), multiple
pregnancy rate (MPR), abortion rate (AR), live birth rate (LBR), ectopic
pregnancy rate (EPR), gestational age, preterm labor rate, mode of
delivery, sex ratio, congenital malformation, low birthweight rate and
birthweight were compared. IR was defined as the number of gestational
sacs on ultrasound divided into the total number of transferred
blastocysts. Clinical pregnancy was considered as a gestational sac seen
by vaginal ultrasound scan by 6-7 weeks of gestation, while multiple
pregnancy was described as having more than one gestational sac.
Meanwhile, abortion was the spontaneous cessation of a clinical
pregnancy, and live birth was defined as delivery of a live fetus at
gestational age ≥ 24 weeks.