Background: Many guidelines have been issued regarding the number of embryos to be transferred after in vitro fertilization (IVF), but patients and clinicians may be reluctant to accept or offer a single embryo transfer due to the expected lower chance of pregnancy or live birth. This study was aimed to provide additional information on cycle outcome according to the number and quality of thawed transferred blastocysts. Methods:A retrospective cohort study was designed to collect the data of 505 patients who performed the first frozen blastocysts transfer at Tam Anh General Hospital from June 2018 to September 2019. One good-quality embryo was transferred for 121 patients (Group 1), two good for 214 patients (Group 2), one good and one poor for 112 patients (Group 3), one good and two poor for 25 patients (Group 4), and one or two poor for 33 patients (Group 5). Results:The pregnancy rate was 71.9%, 74.8%, 69.4%, 84.0%, and 39.4% in Group 1–5, respectively. The multiple pregnancy rate was 36.9%, 16.9%, and 32.0% in Groups 2–4, respectively, higher than Group 1 (4.9%). The live birth rate was 55.6%, 50.9%, and 60.0% in Group 2–4, respectively, but not significantly different from the Group 1 (47.9%). Conclusions:Transferring an additional good or poor embryo, along with a good embryo, does not increase the live birth rate while the incidence of multiple pregnancies rises significantly.

Aims of the study were to describe main outcomes (clinical, ongoing single and multiple pregnancy and live birth rates) following frozen blastocyst transfer performed for the first time among women aged less than 35 years old and analyzed according to both quantity and quality of the embryos. A descriptive cross-sectional study was applied to collect and analyze available data of 505 patients who performed transfer of frozen blastocysts for the first time between June, 2018 and September, 2019 at the Assisted Reproductive Technology Centre of Tam Anh General Hospital. One good quality embryo was transferred for 121 patients (Group 1), 2 good quality embryos for 214 patients (Group 2), 1 good and 1 poor quality embryo for 112 patients (Group 3), 1 good and 2 poor quality embryos for 25 patients (Group 4) and 1 or 2 poor quality embryos for 33 patients (Group 5). Main results showed that the pregnancy rate was 71.9%, 74.8%, 69.4%, 84.0% and 39.4% in Group 1, 2, 3, 4 and 5, respectively. The rate of multiple pregnancy was 36.9%, 16.9%, and 32.0% in Group 2, 3, and 4, respectively, higher than in Group 1 (4.9%). Meanwhile, the live birth rate was 55.6%, 50.9%, and 60.0% in Group 2, 3 and 4, respectively, but not significantly different from the live birth rate in Group 1 (47.9%). In conclusion, pregnancy and live birth rates were not significantly different following transfer of 1 or 2 good quality blastocysts while the rate of multiple pregnancy was significantly increased following the transfer of 2 good quality ones. Transfer of 1 or 2 poor quality embryos in addition to 1 good embryo did not significantly improve the pregnancy rate.