Introduction
The primary goal of assisted reproduction technology (ART) is the birth
of one single healthy child at a time, while multiple pregnancies were
considered as the most serious adverse outcome related to ART,
associated with increased risks of maternal and fetal morbidity1. Risks associated with multiple pregnancies include
higher rates of cerebral palsy, preterm delivery, and low birth weight,
perinatal death compared with singleton pregnancies 2.
The most effective way to minimize the incidence of multiple pregnancies
is single embryo transfer (SET).
The developments of extended embryo culture and the introduction of
vitrification have allowed the widespread application of SET at the
blastocyst stage and surplus blastocysts to be vitrified for subsequent
frozen-thawed blastocyst transfer (FBT) 3, 4. While
single blastocyst transfer (SBT) is commonly adopted in fresh cycles,
double blastocyst transfer (DBT) remains preferable in frozen-thawed
blastocyst transfer (FBT) cycles due to the concerns of reduction of
live birth rate (LBR) 5. Previous studies reported
conflicting results when comparing clinical
pregnancy rate (PR) and LBR of
SBT with DBT in frozen-thawed cycles.
Some investigators demonstrated no significant differences
in PR and LBR between SBT and DBT6, 7, while some studies indicated SBT met a lower PR
and a lower LBR compared to DBT 5, 8. Nevertheless,
all of these studies supported that SBT significantly decreased the
multiple pregnancy rate (MPR).
On the other hand, embryo quality has been reported as a major predictor
of IVF success rates 9. It is well established that
poor quality embryo (PQE) has a lower implantation potential than good
quality embryo (GQE). However, we may confront a dilemma in clinical
practice, whether it would be worthwhile to transfer an additional PQE
with a GQE when the decision concerns embryo quality and number of
embryos. In particular, patients in certain situations (advanced age,
failed repeatedly) commonly resulted in only PQEs with one or no GQE.
Moreover, these patients with poor prognosis were associated with
limited chance of conception and increased risks of obstetrical and
neonatal complications 10, 11.
Therefore, the objective of this study was to evaluate the effect of
DBT with one GQE plus one PQE on
outcomes in women undergoing FBT stratified by age and cycles of ET.
This information would be beneficial for clinicians making transfer
policy for patients with different prognosis. It will also promote the
reduction of overall MPR without impairment of LPR.