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.