Discussion
This study indicated that double FBT
with one GQE plus one PQE increased
LBRs mainly in patients aged 35 and over and in patients received at
least 3 cycles of ET when compared with
single
FBT with only one GQE. Notably, MPR was significantly higher in group GP
than in group G regardless of age or prior ET cycles. MR remained
comparable no matter two groups were stratified by age or cycles of ET
or not.
Several studies have evaluated the impact of double blastocyst transfer
(DBT) on clinical outcomes compared with single blastocyst transfer
(SBT). Dobson and colleagues demonstrated DBT with one PQE plus one GQE
does not increase LBR but increases MPR when compared with SBT with a
TQE during fresh or frozen blastocyst transfer 18.
However, the only confounder they have adjusted for OR was age. There
were likely some other factors which would confound for the results as
other studies have reported 19, 20. Our study also
resulted in no difference in LBR (OR:0.93, 95%CI:0.77-1.11) between two
groups when only adjusted for age before PS matching. Wintner and
colleagues also concluded no statistically significant difference in LBR
between these two groups 21. However, their study was
performed in fresh cycles with ET at cleavage stage or blastocyst stage,
which might differ from FBT 22. On the other hand,
El-Danasouri and colleagues found that transferring an impaired quality
embryo along with a good quality embryo significantly lowered both the
pregnancy rate and implantation rate, than transferring the good quality
embryo alone 23. However, their study did not
demonstrate a statistically significant difference. In contrast to their
reports, some investigators demonstrated that transferring two
blastocysts in FBT cycles lead to a higher PR, a higher LBR and no doubt
a higher MPR 5, 8, which is consistent to our results.
In spite of different results in LBR, aforementioned studies concluded
consistently that double FBT achieved a significantly higher MPR than
single FBT.
Two prior studies have compared the outcomes of DBT with SBT in advanced
maternal age. One study found that DBT resulted in a higher live birth
than SBT for women aged 35 years and over undergoing vitrified-warmed
cycles 6. Another study indicated eSBT is associated
with similar LBRs compared to the entire DBT cohort, but the subgroup of
women who had elective DBT achieved a higher LBR and a higher MP in
advanced maternal age 24. In accordance to their
results, our study also observed DBT with one GQE plus one PQE achieved
a higher LBR than SBT with only one GQE in women aged 35 and over but
not in women under 35 years of age. Our data showed that DBT maintained
a similar PR, MPR, MR and LBR between the subgroups stratified by 35
years of age, whereas SBT resulted in a significantly lower LBR due to a
lower trend in PR and a statistically higher miscarriage rate. The
miscarriage rate significantly increased may possibly because the
prevalence of aneuploidy rose along
with maternal age 25. Poor quality blastocysts owing
to age-related decline in oocyte quality were assessed 25.5% euploid
compared with 56% of the top-quality blastocysts 26.
Despite higher incidence of aneuploidy and a lower implantation than
good quality blastocyst, poor quality blastocysts still contributed an
overall increase of live births 27.
Few studies have reported the comparison of double FBT versus single FBT
in women failed repeatedly. A study performed by McLernon and his
colleagues to develop the prediction model to estimate the chances of a
live birth implied the association between number of complete cycles
with live birth 28. Although it didn’t meet the
definition of recurrent implantation failure, patients underwent at
least 3 cycles of embryo transfer implied difficulties of conception
with various reasons 10. Our study found that DBT of
PQE with GQE achieved a
significantly higher LBR in women
received over 3 cycles of ET due to a higher PR and a similar MR
compared with SBT. The possible explanation of a higher PR might be that
the promotion of interaction between embryo and endometrium by an
additional embryo led to a more favorable endometrial receptivity29. Anyway, it indicated that poor quality blastocyst
had implantation potential to provide additional increase of LBR and
should be vitrified for future use in patients with poor prognosis.
A main strength of our study is that it included the largest number of
patients on this topic to-date. Second, PS matching was conducted to
control for potential confounders which might have effects on the
outcomes. It has been proofed that PS matching provides an approach to
mimic random assignment as RCT and is superior to conventional
regression-based methods in a real world observational study15. Third, the comparisons were not only performed in
overall groups, but were also explored in advanced maternal age and in
women received at least 3 cycles of ET.
Our study was limited by its retrospectively observational design, and
patients’ information were previously recorded by hospital with some
missing data. Though PS matching was performed to evaluate the effects
of DBT with mixed quality embryo independently from other confounders,
the sample decreased after PS and the loss of unmatched cases might have
unforeseen effects. Accordingly, results by multivariable GEE models to
adjust potential confounders before PS matching was presented
relatively.