Introduction
With the development of assisted reproductive technologies, particularly
in embryo culture and cryopreservation, the clinical pregnancy rate
(CPR) is increasing along with the multiple pregnancy rate (MPR).
Multiple
pregnancy
is considered the most significant adverse event associated with ART and
is linked to an increased risk of maternal and neonatal morbidity.
Reducing the number of transferred embryos is a key factor in reducing
multiple pregnancies.1 However, this method has not
been widely used in clinical practice due to concerns pertaining to the
lower pregnancy rate following the
reduction of the number of transferred embryos. Compared to
cleavage-stage embryo, extending embryo culture to blastocyst allows for
better evaluation of the implantation potential of embryo, and the
implantation rate (IR) of blastocyst is higher.2-4Therefore, selective single top-quality blastocyst transfer should serve
as a practical strategy in reducing the number of transferred embryos
while maintaining CPR. Previous findings have suggested that comparable
CPR could be achieved in a clinical setting when utilizing elective
single blastocyst transfer in regard to patients with a good prognosis.
Although live birth rate (LBR) equivalence was not demonstrated, it was
thought the additional complications associated with multiple gestations
outweighed the potentially higher LBR.5 Moreover,
frozen single blastocyst transfer resulted in a higher CPR compared to
that of fresh
single
blastocyst transfer in ovulatory women with a good
prognosis.6 In advanced female age (≥ 40 years),
single blastocyst transfer and double blastocyst transfer achieved
similar CPR and LBR, while MPR was lower in the single blastocyst
group.7 Although research on blastocyst transfer has
been on the rise recently, these studies did not comprehensively analyze
the effects of number and quality of transferred blastocysts as well as
female age on pregnancy and clinical outcomes. In the present study, the
effects of number and quality of transferred blastocysts and female age
on clinical outcomes are compared in order to determine a more
appropriate blastocyst transfer policy to decrease MPR while maintaining
LBR.