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.