Hello and thank you for your question.
I should note that Dr. Rosenwaks is a leading authority in IVF and the
Cornell Weill group is one of the world leaders in the field.
Blastocyst transfer is currently more common than oocyte, but it's
reasonable to assume that he has good reasons for the change in
As to your question, the oocyte v. blastocyst choice is a choice
between viability (the longer the fertilized egg grows in vitro the
greater risk something will go wrong, which probably explains why Dr.
Rosenwaks tried the earlier implant) and reducing multiple births (the
sooner the fertilized egg is implanted the greater the chance it will
multiply into separate embryos, i.e. twins, triplets, etc.).
Here's what a good survey article (worth reading in its entirety) says
about the choice:
Extended embryo culture
"During the past few years the increasing success rates associated
with IVF have led to an increased interest in reducing the incidence
of multiple-gestation pregnancies. As laboratory techniques have
advanced, extended embryo culture has been adopted by most IVF centers
with embryo transfer occurring now most routinely on the third day
after oocyte retrieval. Commercially available media that permits
embryo development beyond the 8-cell stage has led to some clinics
extending embryo culture to the blastocyst stage (day 5 or 6 after
oocyte collection). The potential benefit of extended culture would be
the reduction of multiple births through improved embryo selection
. However if clinics routinely transfer more than 2 blastocysts,
then the potential benefit of extended embryo culture may not be
realized. Blastocyst transfer may also increase the rate of
monozygotic twinning (including monoamniotic twins) [91,92].
Furthermore, patients whose embryos fail to reach blastocyst in
culture may have conceived with a traditional day 2 or day 3 embryo
transfer . Although blastocyst culture remains promising, the
ideal means by which to integrate blastocyst culture into an IVF
program awaits further refinement .
90. Langley MT, Marek DM, Gardner DK, et al.: Extended embryo culture
in human assisted reproduction treatments. Hum Reprod 2001,
91. Peramo B, Ricciarelli E, Cuadros-Fernandez JM, et al.: Blastocyst
transfer and monozygotic twinning. Fertil Steril 1999, 72:1116-1117.
92. Sheiner E, Har-Vardi I, Potashnik G: The potential association
between blastocyst transfer and monozygotic twinning. Fertil Steril
93. Racowsky C, Jackson KV, Cekleniak NA, et al.: The number of
eight-cell embryos is a key determinant for selecting day 3 or day 5
transfer. Fertil Steril 2000, 73:558-564.
94. Gardner DK, Schoolcraft WB, Wagley L, et al.: A prospective
randomized trial of blastocyst culture and transfer in in-vitro
fertilization. Hum Reprod 1998, 13:3434-3440.
Here are links to research related to this issue in which Dr.
Rosenwaks' research is cited.
Search terms used (in scholar.google.com ):
fertility ivf blastocyst oocyte rosenwaks
Thanks again for letting us help.
Google Answers Researcher