Interpretation
The clinical results of the total patient population indicated that group G had the highest IR, lowest MPR and similar CPR, AR and LBR among groups with good-quality blastocysts, which were similar to those of previous studies.9-11Moreover, group P also had a higher IR, lower MPR, and similar CPR, AR and LBR between groups without good-quality blastocysts, which were also in accord with those of previous studies.12 In regard to double blastocyst transfer, the MPR of groups GG, GP and PP were 56.5%, 36.3% and 33.1%, respectively. The changed trends of pregnancy results for different age groups were observed to be equivalent with those for the total patient population. Accordingly, the obtained results indicated that single blastocyst transfer was an effective embryo transfer strategy in significantly reducing the MPR while maintaining LBR. The results of the logistic regression analysis demonstrated that female age and transferred blastocysts were significantly relative to LBR, and the MPR of groups GG, GP and PP were 67.6%, 41.0% and 40.9%, respectively, in < 35 age group. Therefore, it is suggested that single blastocyst transfer should be recommended rather than any double blastocyst transfer methods, and transferring two good-quality blastocysts should be avoided in young patients. Furthermore, increasing the number of blastocysts transferred classified as the same grade was not found to obviously increase CPR and LBR, however, it significantly increased MPR. The corresponding results were similar to those of previous studies.10, 13, 14
Pregnancy is widely viewed as being dependent on an intimate dialogue mediated by locally secreted factors between a developmentally competent embryo and receptive endometrium. Previous studies have indicated that decidualizing human endometrial stromal cells could selectively recognize the presence of a developmentally impaired embryo and respond by inhibiting the secretion of key implantation mediators (e.g. IL-1β and HB-EGF) and immunomodulators (e.g. IL-5, -6, -10, -11, -17, and eotaxin).15 Impaired human embryos elicited an endoplasmic stress response in human decidual cells, and signals emanating from developmentally competent embryos activated a focused gene network enriched in metabolic enzymes and implantation factors.16 Moreover, competent human embryos triggered short-lived oscillatory Ca21 fluxes, whereas low-quality embryos caused a heightened and prolonged Ca21 response.16 These distinct positive and negative mechanisms may result in a lower IR of poor-quality blastocysts. Additionally, its inhibiting effect may be a superimposed effect resulting in a lower IR of two poor-quality blastocysts than one poor-quality blastocyst. The IR of a single good-quality blastocyst was found to be higher than that of two good-quality blastocysts, which may be because the secretion of implantation factors was insufficient for implantation of the two blastocysts. The IR of GP was lower than that of P and G in groups < 35, 35-39 and total patient population, which was in accord with previous studies.10, 12 The reason for this result may be that biochemical reactions preventing the implantation of the poor-quality blastocyst have a negative influence on the implantation of the good-quality blastocyst. Additionally, a competitive relationship may exist between transferred blastocysts, which results in a lower IR of double blastocysts than one blastocyst. Previous findings have demonstrated that IRs were high in the following order: single good embryo, double good embryos, one good embryo with a poor embryo, single bad embryo and double bad embryos.12 Blastocyst score and proportion of top-scoring blastocyst affected implantation, and the degree of blastocoele re-expansion served as a significant ability in predicting live birth in a warmed single blastocyst transfer cycle.17, 18 These results were similar to our study.
Multiple pregnancy is considered the most significant adverse event associated with assisted reproductive technologies and linked to an increased risk of maternal and neonatal morbidity. In this study, the singleton group had a higher average gestational age and birthweight as well as a lower cesarean section rate, preterm labor rate and low birthweight rate than the twin group. Moreover, the LBR of single blastocyst transfer was similar to that of double blastocyst transfer in good-quality blastocyst transfer groups and poor-quality blastocyst transfer groups. Hence, single blastocyst transfer is recommended in decreasing the risk of maternal and neonatal morbidity caused by multiple pregnancy. Monozygotic twins had a lower gestational age and birthweight in conjunction with a higher preterm birth rate and low birthweight rate compared to dizygotic twins. Therefore, the monozygotic twin deserves more attention in assisted reproductive technologies.
In vitro culture induced precocious X-chromosome inactivation and ICSI induced decrease in number of trophectoderm cells in female blastocysts.19 Sex ratio was significantly higher toward males in the transfer of blastocyst compared to transfers of cleavage stage embryos.19-22 Our findings also indicated the presence of a positive correlation between sex ratio and blastocyst quality, which was significant between good-quality and poor-quality embryo groups. Additionally, blastocyst culture and selective single good-quality blastocyst transfer are being recommended by an increasing number of researchers.6, 10, 23 Thus, this transfer strategy may result in an unbalanced sex ratio of newborns in the future, and further research is required in this area.