1. 129M.V. Sauer (ed.), Principles of Oocyte and Embryo Donation,
DOI 10.1007/978-1-4471-2392-7_10, © Springer-Verlag London 2013
Over the last decade, progressive refinements in
the evaluation of ovarian reserve, controlled ovar-
ian hyperstimulation regimens, embryology lab-
oratory culture systems, as well as embryo
transfer and cryopreservation techniques have
resulted in significant improvements in assisted
reproductive technology (ART) outcomes. With
these advances, an emerging need to maximize
the likelihood of a live birth while minimizing the
risk of multiple gestations has attained paramount
importance, particularly in the case of oocyte
donation. Recently published guidelines from the
American Society for Reproductive Medicine
have stated that in the case of a young oocyte
donor with favorable prognosis, only a single
blastocyst stage or no more than two cleavage
stage embryos be transferred [1]. However, in a
recent analysis, Martin et al. suggested that even
in “best” prognosis oocyte donors from whom at
least two donations had resulted in live birth, the
live birth rates per oocyte retrieved and per
embryo transferred were only 7.3 and 24.6 %,
respectively [2]. Given this staggering degree of
attrition even in the best prognosis patients
and the need to decrease the numbers of
embryos transferred, it is critical that clinicians
E.S. Surrey, M.D.(*) • W.B. Schoolcraft, M.D., HCLD
Colorado Center for Reproductive Medicine,
10290 RidgeGate Circle, Lone Tree, CO 80124, USA
e-mail: esurrey@colocrm.com;
bschoolcraft@colocrm.com
10Blastocyst Versus Cleavage Stage
Embryo Transfer: Maximizing
Success Rates
Eric S. Surrey and William B. Schoolcraft
Key Points
There is an emerging need to maximize•
the likelihood of live birth while minimiz-
ing the risk of multiple gestations, and the
American Society for Reproductive Medi-
cinehas stated that in most cases of oocyte
donation, only a single blastocyst stage or
no more than two cleavage stage embryos
be transferred.
The development of highly specific•
sequential and nonsequential embryo
culture systems as well as meticulous
attention to air quality and laboratory
technique has allowed for routine suc-
cessful development of embryos to the
blastocyst stage.
Evaluation of embryo quality and num-•
ber at the pronuclear and, perhaps more
importantly, at the cleavage stage of
development may serve as an imperfect
predictor for blastocyst development
potential.
Proteomic and metabolomic assess-•
ments of spent culture medium may
soon represent dynamic means of creat-
ing a unique profile of biomarkers to
predict blastocyst viability.

2. 130 E.S. Surrey and W.B. Schoolcraft
and embryologists obtain as much information as
possible about the developmental and implanta-
tion potential of embryos considered for transfer.
The shift to more widespread transfer of blas-
tocyst as opposed to cleavage stage embryos in
good prognosis patients (including oocyte donor
recipients) has represented one of the key factors
in improving outcomes. Indeed, the debate in
oocyte donation has shifted from the question of
whether blastocyst stage transfer is feasible to
whether blastocyst stage transfer should be stan-
dard and cleavage stage transfer the exception.
We will provide evidence to support this conten-
tion in this chapter.
Why Blastocyst Stage Transfer?
There are a host of potential advantages to the use
of blastocyst stage embryo transfer in the oocyte
donation model (Table 10.1 and Fig. 10.1).
Perhaps the most important is the fact that the
embryo can be transferred into the uterus at the
appropriate developmental stage. The tubal envi-
ronment to which the cleavage stage embryo is
exposed in vivo is significantly different with
regard to nutrients and pH than the uterus to
which the blastocyst stage embryo is exposed,
and therefore, transfer at an earlier developmen-
tal stage may inhibit embryonic development [3].
Secondly, uterine contractility progressively
decreases in the luteal phase from the day of hCG
administration with the most profound decline
occurring between 4 and 7 days [4]. This would
theoretically result in a more quiescent state at
the time of blastocyst transfer which could aid
implantation. Thirdly, it appears that full activa-
tion of the genome of the embryo does not occur
until after the cleavage stage [5]. Extending
embryo culture would allow identification of
embryos with an inherent developmental block.
The benefits of extended embryo culture are
clearly dependent on the culture system. The
development of highly specific sequential and
nonsequential systems as well as meticulous
attention to air quality and laboratory technique
has allowed for routine successful development
of embryos to the blastocyst stage in vitro [3, 6].
Perhaps the most compelling reason in favor
of blastocyst transfer is the significantly higher
pregnancy and implantation rates achieved in
comparison to cleavage transfer. The bulk of evi-
dence has been obtained from IVF cycles employ-
ing autologous oocytes, which shall be presented
first. However, one can only assume that out-
comes obtained from oocytes derived from
younger women without inherent fertility problems
Table 10.1 Advantages of blastocyst culture and transfer
in oocyte donation
Enhanced synchrony with uterine environment
Transfer into a more quiescent uterus
Enhanced developmental information
Increased implantation rates
Full activation of embryonic genome
a
b
Fig. 10.1 (a) Photograph of high-quality eight-cell
embryo derived from an oocyte donor 3 days after oocyte
aspiration. (b) Photograph of high-quality expanded blas-
tocyst derived from an oocyte donor 5 days after oocyte
aspiration

3. 13110 Blastocyst Versus Cleavage Stage Embryo Transfer: Maximizing Success Rates
(oocyte donors) would only be higher which is
confirmed by the small number of trials address-
ing this specific population.
Blastocyst Transfer: IVF Outcomes
Two studies both published in 2004 evaluating
elective single embryo transfer (eSET) in good
prognosis patients are illustrative of the potential
advantage of blastocyst transfer. Thurin et al. ran-
domized 611 women less than 36 years of age
with at least two good-quality embryos to eSET
or double embryo transfer, of which 97.2 %
underwent transfer on day 2 or 3 (the majority on
day 2) [7]. The implantation rate for the first
eSET was 33.6 %. In contrast, Gardner et al. ran-
domized 48 women with similar baseline charac-
teristics and at least 10 follicles >12 mm in
diameter on the day of hCG administration to
elective single or double day 5 blastocyst stage
embryo transfers [8]. In this case, the implanta-
tion rate for the single blastocyst transfer group
was 60.9 %.
A host of prospective randomized trials have
compared cleavage to extended stage embryo
transfer, the majority of which demonstrated
improved outcomes with the latter [9–24]. One of
the few trials which reported lower live birth rates
with blastocyst transfer noted similar implanta-
tion rates for both groups [15]. Interestingly, all
blastocyst transfers in this study were performed
on day 6, which may be a confounding variable.
Indeed, others have demonstrated that day 5 blas-
tocysts may be better synchronized with endome-
trial development than more slowly developing
embryos transferred on day 6, resulting in higher
pregnancy rates with day 5 transfer [25, 26].
Perhaps more telling are the results of pro-
spective randomized trials comparing elective
single cleavage to blastocyst stage embryo trans-
fer. Papanikolaou et al. randomly assigned 351
women under 36 years of age to transfer of a sin-
gle cleavage stage (day 3) or blastocyst stage (day
5) embryo [27]. The study was terminated after
an interim analysis demonstrated significantly
higher ongoing pregnancy rates (58 % vs. 41 %,
P=0.02; 95 % CI 1.06–2.66) and live birth rates
(56 % vs. 38 %, P=0.01; 95 % CI 1.09–2.18) per
embryo transfer procedure in the blastocyst
group. Subsequently, Zech and coworkers per-
formed a similar study of 227 women £36 years
of age undergoing a first or second IVF cycle,
resulting in ³5 fertilized oocytes [28]. A
significantly higher implantation rate per embryo
transfer was achieved with blastocyst transfer
(35.6 % vs. 23.7 %, P<0.05). Guerif and cowork-
ers recently completed a prospective study of 478
couples assigned to day 2 eSET or single blasto-
cyst transfer on day 5 or 6 [29]. It is important to
note that patients were assigned on a “voluntary
basis” which represents a confounding variable.
Nevertheless, the delivery rate per fresh embryo
transfer was again significantly higher after sin-
gle blastocyst transfer (36.7 % vs. 25.1 %,
P<0.01) (Table 10.2). It is interesting to note that
a recent meta-analysis of live birth rates after
elective single cleavage stage embryo transfer in
prospective randomized trials described a live
birth rate of 26.7 % [30].
Two recent meta-analyses addressing this
issue with different designs and reaching differ-
ent conclusions have been published. An updated
Cochrane review evaluated randomized trials of
early cleavage (day 2/3) versus blastocyst (day
5/6) stage transfers [31]. Sixteen of the 45
identified trials met inclusion criteria and were
analyzed. Interestingly, there was no difference
in live birth rates per couple in seven randomized
clinical trials (day 2/3: 34.3 % vs. day 5/6:
35.4 %; OR 1.16, 95 % CI 0.74–1.44). This phe-
nomenon held true for “good prognosis” patients
as well. There was also a greater likelihood of
having no embryos to transfer in the blastocyst
Table 10.2 Comparative implantation rates (IR) result-
ing in live birth after elective single cleavage (eSET) or
blastocyst stage (eBT) embryo transfer
First author (Ref.) eSet eBT P
N
IR/ET
(%) N
IR/ET
(%)
Papanikolaou [27] 176 43 176 58 0.04
Zech [28] 99 23.2 128 32.8 <0.05
Zech [28]a
86 25.6 76 40.8 <0.05
Guerif [29] 243 25.1 235 36.7 <0.01
a
Excellent-quality embryos only

4. 132 E.S. Surrey and W.B. Schoolcraft
group, although this phenomenon was not
significantly different for good prognosis patients.
This analysis did not evaluate implantation rates
per se.
In a more recent meta-analysis, eight random-
ized trials met stricter inclusion criteria of truly
randomized design, transfer of equal numbers of
embryos between the two groups and included
only studies which had been previously published
as full text in a peer review publication [32]. In
this analysis, live birth rates were significantly
higher after blastocyst versus cleavage stage
transfers (OR 1.39, 95 % CI 1.10–1.76, P=0.005).
Given the design of this meta-analysis with equal
numbers of embryos transferred in each group,
these data would more closely approximate an
assessment of relative implantation potential.
Clearly, there are weaknesses with both analy-
ses. The most critical of which for the purpose of
this discussion is the fact that neither address out-
comes of oocyte donor cycles. Even subset analy-
sis of “good” prognosis patients cannot be
compared to oocyte donors [31]. The average age
of oocyte donors would be presumably less than
that of IVF patients, and more importantly, oocyte
donors would have no underlying history of infer-
tility. In addition, outcomes from day 5 and 6
blastocyst transfer were typically combined,
which represents a confounding variable as pre-
viously described [25].
Blastocyst Transfer: Oocyte Donation
Outcomes
As previously mentioned, the outcome data for
blastocyst versus cleavage stage embryo transfer
in the oocyte donation model is limited. We are
aware of no prospective randomized trials
specifically addressing this patient subset.
Schoolcraft and Gardner reported a retrospec-
tive series of 229 patients undergoing oocyte
donation at the Colorado Center for Reproductive
Medicine, of whom 116 underwent day 3 transfer
and 113 underwent day 5 transfer [33]. Mean
ages of donors and of recipients were similar
between the groups. The average blastocyst
development rate was 58.7 %. Implantation rates
resulting in documented fetal cardiac activity per
embryo transfer were significantly higher in
patients receiving a blastocyst transfer (65.0 %
vs. 41.6 %, P<0.01). Clinical pregnancy rates
per retrieval were also significantly higher after
blastocyst transfer (87.6 % vs. 75.0 %, P<0.05)
despite transferring a significantly lower mean
number of embryos (Table 10.3 and Fig. 10.2).
These results were confirmed by Shapiro and col-
leagues who reported a mean implantation rate of
52.8 % with a 66.7 % ongoing pregnancy rate in
47 donor cycles after blastocyst transfer on either
day 5 or 6 [34].
Table 10.3 Oocyte donation: day 3 versus day 5 embryo
transfer: cycle characteristics
Day 3 Day 5 P
No. of donor cycles 116 113 –
Donor age
(mean±SEM)
28.8±0.44 27.8±0.41 NS
Recipient age
(mean±SEM)
39.9±0.43 41.3±0.41 NS
Blastocyst develop-
ment (%)
– 58.2 –
Embryos transferred
(mean±SEM)
3.2±0.05 2.1±0.04 <0.01
Embryos frozen
(mean±SEM)
5.2±0.59 5.6±0.43 NS
Adapted from Schoolcraft and Gardner [33]
P < 0.05
P < 0.01
Clinical
pregnancy/retrieval
Implantation/embryo
transfer (+ fetal heart)
Percent
Oocyte donation cycle outcomes
day 3 versus day 5 transfer
Day 3 Day 5
0
100
90
80
70
60
50
40
30
20
10
75 %
87.6 %
41.6 %
65 %
Fig. 10.2 Oocyte donation cycle outcomes comparing
day 3 versus day 5 embryo transfer in a large retrospective
series (Adapted from Schoolcraft and Gardner [33])

5. 13310 Blastocyst Versus Cleavage Stage Embryo Transfer: Maximizing Success Rates
A more contemporary review of all oocyte
donation cycles performed at the Colorado Center
for Reproductive Medicine from 2004 through
2009 revealed that the implantation rate from 236
day 3 transfers was 45.4 % and that of 828 day 5
transfers was 72.5 %. The ongoing pregnancy
rate after cleavage stage transfers was 70.3 % in
comparison to 87.4 % after blastocyst transfer.
A recent retrospective analysis compared cleav-
age (day 3) to blastocyst (day 6) stage embryo
transfer in 93 consecutive oocyte donation cycles
[35]. Once again, significantly higher implantation
rates (64±6 % vs. 27±7 %, P<0.01) and clinical
pregnancy rates (73 % vs. 40 %, P<0.01) were
obtained after blastocyst transfers. Even after
oocyte vitrification, implantation rates in oocyte
donor cycles after blastocyst development and
transfer were extremely encouraging [36].
In contrast, Soderström-Anttila and Vilska
reported upon a 5-year experience with elective
cleavage stage embryo transfer in both anony-
mous and non-anonymous oocyte donation cycles
[37]. An implantation rate of 43.2 % per embryo
transfer was reported. Previously, Mirkin et al.
reported a 22 % implantation rate with day 3
transfers in oocyte donation cycles [38].
There are several important confounding vari-
ables in the aforementioned trials. The lack of
appropriately designed prospective randomized
trials is a weakness. However, given the retro-
spective data from oocyte donors and prospec-
tive trials derived from good prognosis IVF
patients, there is little to suggest that day 3 trans-
fer is more advantageous in the oocyte donation
model given an appropriate embryology labora-
tory setting. The combination of outcomes from
day 5 and 6 blastocyst embryo transfers in these
trials remains problematic. Although Shapiro
et al. have demonstrated that clinical pregnancy
rates from day 5 blastocyst transfers are superior
to day 6 transfers in autologous IVF cycles, they
noted the opposite phenomenon with oocyte
donor cycles [26]. This may reflect a higher
degree of synchrony between embryo and endo-
metrium based on the specific endometrial prep-
aration protocol employed. These data have not
been confirmed, and one would remain con-
cerned that transfer of more slowly expanding
blastocysts may also reflect compromised
developmental potential.
A third confounding variable, which has not
been addressed in any of the aforementioned tri-
als, is the impact of male age. It can be assumed
that in the average oocyte donation cycle, pater-
nal age would be elevated in comparison to “good
prognosis” IVF cycles. Several studies have sug-
gested that increasing paternal age (particularly
>50 years) is associated with an adverse outcome
in oocyte donor cycles [39, 40]. Both trials dem-
onstrated a deleterious effect on blastocyst devel-
opment rate. However, this finding has not been
universally demonstrated [41].
The Case Against Blastocyst Transfer
Given the aforementioned evidence in favor of
blastocyst transfer in the oocyte donation model,
there remain several arguments which have been
historically made in opposition to this approach:
1. A high percentage of otherwise viable embryos
on day 3 fail to develop to the blastocyst
in vitro and would be “lost” for transfer.
2. Cryopreservation of supernumerary blastocyst
stage embryos results in lower survival rates
than at earlier developmental stages, resulting
in a decline in overall cycle efficiency.
3. Transfer of embryos at the blastocyst stage
may be associated with an increased risk of
monozygotic twinning.
We will address each of these issues.
The contention that viable day 3 embryos will
not survive in vitro to the blastocyst stage and
would have a greater likelihood of surviving in the
uterus clearly cannot be directly tested since the
same embryo cannot be evaluated in two places at
once. The failure of embryos to develop in vitro
may indeed be secondary to a suboptimal labora-
tory environment. However, in an optimal labora-
tory setting, this phenomenon may also be due to
embryos with inherent genetic and metabolic
impairment leading to arrested development. Other
factors to consider would be those of advanced
paternal age, severe sperm abnormalities, and the
impact of cycles with an older (typically known)
donor. In their meta-analysis, Blake et al. reported

6. 134 E.S. Surrey and W.B. Schoolcraft
that the likelihood that couples would have no
embryos to transfer is significantly higher for blas-
tocyst versus cleavage stage embryos [31].
However, when these investigators limited their
analysis to good prognosis IVF patients, this dif-
ference was not statistically significant (OR 1.58;
95 % CI 0.65–3.82). These trials did not include
oocyte donation cycles, a situation with a presum-
ably better prognosis than “best case” autologous
IVF patients. Indeed, we had previously reported
that 58 % of fertilized donor oocytes undergoing
extended culture in sequential medium reached the
blastocyst stage, of which 84 % were felt to be of
high quality [33].
It is not necessary to commit to blastocyst
transfer in all cycles without exception, however.
Evaluation of embryo quality and number at the
pronuclear and, perhaps more importantly, at the
cleavage stage may serve as an imperfect predic-
tor for blastocyst development potential. Neuber
et al. reported a high correlation between pronu-
clear symmetry, early cleavage, and subsequent
blastocyst development [42]. Dessolle and
coworkers created a predictive model for failed
blastocyst development based on fertilization
technique, female age, as well as number and
quality of day 3 embryos [43]. This view has not
been uniformly accepted in that others have
suggested that morphologic assessment of
embryos at the pronuclear or cleavage stage is
poorly predictive of the likelihood of blastocyst
development [44, 45].
The ability to efficiently cryopreserve super-
numeraryembryosenhancestheoverallefficiency
of any given oocyte aspiration procedure. If out-
comes with blastocyst stage cryopreservation
were significantly compromised compared to
pronuclear or cleavage stage freezing, then
benefits of fresh blastocyst transfer would be
neutralized. Meta-analyses have reported that the
rate of embryo freezing was higher at days 2–3
versus days 5–6 [31, 32]. However, these reports
only suggest that more embryos were available
for cryopreservation at earlier developmental
stages, as would be expected, but not that out-
comes were enhanced from subsequent transfers.
Guerif and coworkers previously noted that in
their program, fresh elective single blastocyst
transfer pregnancy rates were higher than elec-
tive cleavage stage embryo transfers, but once
frozen embryo transfers were included, cumula-
tive delivery rates were not significantly different
between the two groups [29].
However, outcomes from blastocyst cryo-
preservation are not consistent among laborato-
ries, and published reports cannot be universally
applied. In addition, it is important to note that
results from earlier studies may not reflect cur-
rently employed techniques. Veeck et al. reported
a 76.3 % survival rate of blastocysts cryopre-
served using slow-freeze techniques with an
ongoing clinical pregnancy rate of 59.2 % [46].
In a retrospective analysis from this same group,
clinical pregnancy rates (64.2 % vs. 37.4 % vs.
42.1 %, P<0.05) and implantation rates (38.5 %
vs. 15.2 % vs. 17.1 %, P<0.05) per transfer were
significantly higher after transfer of thawed blas-
tocysts in comparison to thawed cleavage or pro-
nuclearstageembryos[47].Thereisdisagreement
among investigators as to whether there are dif-
ferences in outcomes from blastocysts cryopre-
served on day 5 versus day 6 when transferred to
an appropriately prepared endometrium [26, 48].
An alternative approach for clinics uncomfort-
able with blastocyst slow-freeze techniques is to
freeze supernumerary embryos at the pronuclear
or cleavage stage and then allow subsequently
thawed embryos to grow to the blastocyst stage
before transfer. Employing this approach with
oocyte donors, Shapiro and colleagues reported
similar implantation and pregnancy rates as with
fresh transfers [49]. The disadvantage of this
approach is the inability to select embryos for
fresh transfer from the full cohort of embryos
which could have a deleterious impact on the
success of the fresh embryo transfer.
The introduction of successful blastocyst
vitrification has significantly improved the
efficiency of cryopreservation and enhanced out-
comes due to the elimination of intracellular ice
crystal formation [50, 51]. In a recent review and
meta-analysis, Loutradi et al. reported a post-
thaw blastocyst survival rate that was significantly
higher using vitrification as opposed to slow-
freeze techniques (OR 2.2, 95 % CI 1.53–3.16)
[52]. At the Colorado Center for Reproductive

7. 13510 Blastocyst Versus Cleavage Stage Embryo Transfer: Maximizing Success Rates
Medicine, we have reported a 97.8 % survival
rate after blastocyst vitrification even after tro-
phectoderm biopsy [53]. In fact, some investiga-
tors have reported significantly higher pregnancy
and implantation rates in nondonor IVF cycles
after transfer of vitrified and warmed blastocysts
than after fresh transfer [54]. This may be due to
the presence of a more receptive endometrium in
the prepared frozen embryo transfer cycle.
However, in the case of oocyte donation cycles,
endometrial preparation of the recipient would be
similar for a fresh or frozen transfer cycle making
this issue less relevant.
The final concern which has been raised
regarding blastocyst transfer is the question of
whether prolonged culture is associated with any
inherent increased pregnancy risks. Several inves-
tigators have suggested that the incidence of
monozygotic twinning may be increased after
blastocyst versus cleavage stage embryo transfer
[55–57]. This has been attributed to a possible
increase in the hardness of the zona pellucida due
to prolonged in vitro embryo culture. It is inter-
esting to note that in two more recent studies, the
incidence of monozygotic twinning was no dif-
ferent between blastocyst and cleavage stage
transfers [58, 59]. This change may be reflective
of advances in culture medium. In addition, these
data are not derived from oocyte donation cycles,
and therefore, we are forced to extrapolate to that
model.
Blastocyst Selection: Is Morphology
Enough?
Although it would appear from the evidence pro-
vided that implantation rates with blastocyst
transfer are significantly enhanced over day 3
transfer in both autologous and donor IVF cycles,
the results remain imperfect. In an effort to maxi-
mize success while minimizing multiple preg-
nancies, elective single embryo transfer clearly is
ideal. Thus, enhancing the accuracy of embryo
selection techniques is critical to achieving this
goal.
Assessments of morphology and developmen-
tal rate have been the mainstays of this approach.
We have previously discussed the merits of day 5
versus day 6 fresh blastocyst transfers. Employing
a morphologic grading system based on the
degree of blastocyst expansion along with the
development and architecture of both the inner
cell mass and trophectoderm, Gardner et al. dem-
onstrated a relationship between blastocyst grade
and implantation [60]. When two top-quality
blastocysts were transferred (³3AA) (69 % of
patients), the implantation rates were significantly
higher than the 15 % of patients who had only
lower-scoring blastocysts (<3AA) transferred
(69.9 % vs. 78.1 %).
In the setting of oocyte donor cycles, the pre-
dictive value of morphologic assessment is even
less clear. In reviewing all oocyte donor cycles
performedattheColoradoCenterforReproductive
Medicine from 2004 to 2009, we noted that
implantation rates after transfer of expanded but
not perfect blastocysts were similar to those
transferred which were felt to be perfect in qual-
ity and not dramatically different than in the small
number of patients with only morulae available
to transfer (Table 10.4).
In the best of circumstances, blastocyst mor-
phology is not completely predictive of outcome.
New tools, the details of which are beyond the
scope of this chapter, may add additional infor-
mation regarding the embryo in order to enhance
the selection process. Aneuploidy screening may
represent one of these approaches. The incidence
of aneuploid embryos increases significantly
with age, a phenomenon which one would
assume would be negated with the use of a young
oocyte donor. Indeed, Fragouli et al. noted a low
aneuploidy rate (3 %) using comparative genomic
hybridization techniques after polar body biopsy
of oocytes derived from donors with an average
age of 22 years [61]. However, these data do not
reflect the impact of advanced paternal age,
which is more commonly associated with oocyte
donation cycles and may play a role in increas-
ing the incidence of aneuploid embryos despite a
high percentage of euploid oocytes. Exciting
new validated techniques allowing for compre-
hensive chromosomal screening of blastocyst
stage embryos have been shown to increase implan-
tation rates by 50 % compared to contemporary

8. 136 E.S. Surrey and W.B. Schoolcraft
autologous IVF cycles [62, 63, 64]. These tech-
niques have primarily been employed in couples
with recurrent implantation failure, unexplained
recurrent pregnancy loss, and advanced maternal
age and not in the oocyte donation model or in
the average younger infertile patient. However,
if the value of this approach is confirmed in
appropriately designed prospective randomized
trials, a case could be made for future investiga-
tion of this technique in other models as well.
Indeed, analysis of blastocyst gene expression
may take us beyond simple aneuploidy screen-
ing in creating a profile which predicts implanta-
tion potential [65].
In addition, noninvasive approaches to the
assessment of the viability of embryos which
may be morphologically similar are areas of
intense investigation. Proteomic and metabolo-
mic assessments of spent culture medium may
represent dynamic means of creating a unique
profile of biomarkers to predict blastocyst viabil-
ity [66, 67]. If validated, these approaches would
certainly have application in the oocyte donation
model as well.
Summary
Oocyte donation represents the most consistently
successful therapy in the assisted reproductive
technologies. As success rates have improved,
multiple pregnancy rates have also increased. As
a result, the need to more effectively select a sin-
gle embryo for transfer without compromising
efficacy has become a critical issue. Extending
embryo development to the blastocyst stage has
represented a clear advance in this regard.
Refinements in culture medium and laboratory
techniques as well as increased competence in
vitrification technology serve to reinforce this
approach. New technologies in genomics, pro-
teomics, and metabolomics will allow clinicians
and embryologists to create a profile of the
implantation potential of an embryo which
extends beyond an assessment of morphology
alone. The question, therefore, has shifted from
which situations would be appropriate for blasto-
cyst transfer to which situations, if any, would not
be appropriate for blastocyst transfer in oocyte
donation cycles.
Table 10.4 Oocyte donation outcomes and blastocyst quality at Colorado Center for Reproductive Medicine
(2004–2009)
Stage Cycles Total embryos transferred Ongoing pregnancy (%) Implantation (%)
Only morulae 7 21 100 71.4
Only early (1,2,2/3)a
29 66 69 53
Only advanced but not perfect
(AB, BA, BB)a
93 189 84.9 72
Only perfect (AA)a
453 866 91.6 77.6
a
Based on scale described by Gardner et al. [60]
Editor’s Commentary
Blastocysts have taken center stage in egg
and embryo donation since the first report
of a birth in 1984. John Buster, M.D. at
Harbor/UCLA, noted during the early uter-
ine lavage experiments that only recipients
of recovered blastocysts became pregnant
and that the implantation and pregnancy
rates of these transferred embryos were
remarkably high. Of course, the efficiency
of uterine lavage and natural cycles pre-
vented the development of embryo trans-
fers along these lines. Development of the
in vitro methods proceeded, and for the
next two decades, cleavage stage embryos
became the focus and the practice in both
conventional IVF and oocyte donation.
By the mid-1990s, it was becoming increas-
ingly clear that we had a multiple birth
problem in our recipients. Remarkably, and
looking back in retrospect, at that time, the
standard was still to transfer up to five

9. 13710 Blastocyst Versus Cleavage Stage Embryo Transfer: Maximizing Success Rates
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order multiple births were becoming com-
monplace, and many of the recipients were
also older, making the resulting pregnancy
even greater risk. Thus, it was fortunate
that in addition to improvements in embryo
cryopreservation, the development of
extended culture systems that allowed
growth up to the hatching blastocyst stage
emerged. Finally, a return to the original
premise of embryo donation could be real-
ized, that being the transfer of a single
healthy-appearing blastocyst to a well-pre-
pared and synchronized uterus.
Drs. Eric Surrey and Bill Schoolcraft nicely
summarize the improvements in clinical
outcomes resulting from transitioning to a
blastocyst transfer policy for embryo trans-
fer. No different from the lessons of three
decades ago, when it comes to predicting
pregnancy at the time of embryo transfer, it
boils down to selection. Further diagnostic
testing beyond the current embryo mor-
phology assessment promises to add fur-
ther to the efficiency of the process. The
ultimate goal of routinely transferring a
high-quality preimplantation embryo is
now at hand, and with national success
rates consistently above 50 %, it is time to
reexamine whether more than a single
embryo should ever be placed into the
uterus of a recipient.

10. 138 E.S. Surrey and W.B. Schoolcraft
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