Association between the number of morphological top-quality blastocysts developed and live births after single blastocyst transfer in the first fresh or frozen IVF/ICSI cycle

Research question: Is there an association between the total number of top-quality blastocysts (TQB) developed in the first IVF/intracytoplasmic sperm injection cycle (ICSI) and live births after a single blastocyst transfer (SBT)? Design: Pregnancy outcomes from 1336 infertile women who had undergone their first IVF/ICSI treatment and accepted a first-time embryo transfer with a single fresh or vitrified-warmed blastocyst between January 2016 and August 2018 were assessed retrospectively. The restricted cubic splines method was used to evaluate the association between the number of TQB, and ongoing pregnancies and live births. Results: A significant non-linear functional form was found between the number of TQB and the ongoing pregnancies and live births (P < 0.05). The odds of an ongoing pregnancy or live birth were similar, at about 11% or higher for each additional TQB up to five TQB (odds ratio [OR] 1.11; 95% confidence interval [CI] 1.01-1.21). After this, pregnancy outcomes nearly plateaued, indicating that the number of TQB was not related to pregnancy when it was greater than five. Conclusions: The quantity of TQB available for transfer or cryopreservation can provide important predictors for pregnancy and live birth after the first embryo transfer cycle with a single blastocyst. This valuable information may assist with the future application of SBT.