Findings in relation to existing literature
Our eSBT patients had a live birth rate per fresh cycle (52.1%) similar
to that reported after eSBT in younger women,26 which
might imply that once the blastocysts-stage was achieved, pregnancy
outcomes were less effected by maternal age.27,28 In
this regard, despite their age, a subset of these women can still have
embryos cultured to blastocyst-stage and can benefit from policy of
eSET.
The finding in the present study differs from some previous studies
suggesting that eSET can result in a significant lower ongoing pregnancy
rate compared with DET (21.4 versus 40.3%) in unselected IVF
patients.29 Nevertheless, only cleavage-stage transfer
was included in their study, which may have limited their results. The
better outcomes in our work probably reflects marked improvements in IVF
over the past decade. Extended culture to blastocyst-stage transfer
enables more sophisticated assessment of embryo morphology, with better
selection of the embryos more likely to success. Similar to the present
study, Davis et al 30 recruited 45 patients older than
35s undergoing eSBT in a small retrospective study. Of them,
twenty-three patients (51.1%) have an ongoing pregnancy or live
delivery, demonstrating a clear role for SET in this relatively older
IVF population. Another retrospective study also confirmed the
feasibility of eSBT in women with a narrow maternal age (40-43
years).31
Implications for clinical practice
A growing number of women seek IVF over the age of 35
years,32 specifically as the two-child policy was
fully implemented in China, ART has been a beneficial complementary
technology and health service for couples with advanced age. Practical
questions are encountered: if transferring one embryo at a time is
associated with a diminished likelihood of a live birth in women over 35
years? If the woman had two embryos transferred, what is the probability
of twin delivering and the potential risks? Providing precise
information to answer these questions would help couples to decide how
many embryos to transfer.
To further identify the role of blastocyst quality in practice of eSBT,
we stratified our analysis into good- and fair-quality blastocyst
transfer. In older women with at least one good-quality blastocyst, the
live birth rate was similar between the two cohorts. However,
transferring two blastocysts resulted in a large reduction in
implantation rate (from 67.9% to 51.0%) and a great increase in
multiple birth rate (from 1.2% to 44.1%). This observation supports
the hypothesis of embryo-endometrial crosstalk that endometrium may act
like a sensor of embryo quality preventing the implantation or
sustainment of a low-quality or abnormal embryo.33When there was no good-quality blastocyst available, the strategy of
eSBT was also feasible, since additional fair-quality blastocyst did not
increase the rate of implantation or live birth. These data suggested
that in case of two blastocysts were obtained, eSBT should be
encouraged, irrespective of blastocyst quality.34
For women aged over 36, transfer of two blastocysts after initial fresh
IVF/ICSI cycle, the most statistically significant risks are higher
rates of low birth weight and preterm labor. Women with DBT are also at
higher risk for cesarean delivery, though the odds are less
statistically significant. In 2010, a study in Sweden involving more
than 25,000 women receiving IVF, showed that the risk of neonatal death
and morbidity was significantly reduced following the SET
policy.35 Concerned with the worse perinatal outcomes,
there is an urgent need to limit multiple births by reducing embryo
transfer from two to one.36