Introduction
Although there has been a gradual decrease in multiple births after
assisted reproductive technology (ART) across the world, that decrease
is mostly in developed countries.1Twin delivery rates
in China were 27.9% and 27.2% after in vitro fertilization
(IVF)/intracytoplasmic sperm injection (ICSI)
respectively,2 which are higher than that of many
other countries. Elective single embryo transfer (eSET) has been
appeared to be the most effective approach to reduce multiple births
associated with IVF/ICSI.3-5 eSET policy has primarily
been recommended in women of younger reproductive age with a good
prognosis, which is not routinely offered to women aged beyond 35 years
old.6-8 There is fear that the adoption of eSET in
unselected patients will lower pregnancy rates per embryo transfer and
extend the time needed to achieve live birth.
Advanced maternal age is associated with a decreased chance of pregnancy
after IVF and a higher risk of fetal loss, but older women are still at
risk for multiples.9,10 Increasing age aggravates the
risks of unfavorable obstetrics outcomes (e.g. preterm delivery, low
birth weight and perinatal mortality), and this is further so in cases
of multiple pregnancy.11,12 However, patients at
advanced age and physicians are still hesitant to embrace eSBT and wish
to maximize their chance of pregnancy with the transfer of more than one
embryo. Several trials that did recruit older women aged over 36 to make
such a comparison possible.13,14 These two studies,
however, were restricted to cleavage-embryo transfer, impact of
blastocysts transfer on the implications of the policy in that age group
has been fully studied.
Aneuploid embryos, often age dependent, are less likely to continue
development to the blastocyst stage,15 hence
blastocyst culture theoretically would assist the selection of the most
viable embryo. A number of studies have demonstrated significant
differences in implantation and pregnancy rates in favor of extending
the embryo culture to blastocyst-stage transfer.16-18
As extending embryo culture has been a routine practice in many clinics,
it remains to be proven if it is appropriate to consider the transfer of
one blastocyst-stage embryo for women at advanced age. We carried out
the retrospective cohort study to compare the effectiveness of eSBT
versus DBT on the cumulative live birth rates (cLBR) (fresh and frozen
transfers accruing from a single oocyte retrieval) and perinatal
outcomes. We have also assessed the applicability of eSBT by exploring
whether its practice is associated with extending the time to live birth
(TTLB).