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November 9, 2012--------News Archive Return to: News Alerts






Currently, some IVF laboratories screen blastocysts for chromosomal abnormalities by
biopsying trophectoderm (TE) cells, the cells that become the placenta and umbilical
cord, and assessing them with a DNA microarray. However, human embryos are
susceptible to mosaicism, where one group of cells develops differently from a neighboring group due to a spontaneous DNA mutation.

This causes chromosomes to differ not only among TE cells but also between
these beginning placental cells and inner cell mass (ICM) cells, which continue
on to develop into the embryo itself
.





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Value of Second Embryo Biopsy for Women of Advanced Maternal Age

An elegant new study confirms that the most commonly used method of screening for embryo abnormalities following in vitro fertilization (IVF) accurately predicts the success of embryo transplant for younger women, but not necessarily for those 38 or older

Almost 70 percent of aneuploid blastocysts from women aged 38 or older were mosaic, that is they had developed spontaneous DNA mutations.

Currently, some IVF laboratories screen blastocysts for chromosomal abnormalities by taking a biopsy of the trophectoderm (TE) cells, the cells that become the placenta and umbilical cord, and assessing them with a DNA microarray.

However, human embryos are susceptible to mosaicism, in which one group of cells develops differently from a neighboring group due to a spontaneous DNA mutation. This causes chromosomes to differ not only among TE cells but also between these nascent placental cells and inner cell mass (ICM) cells, which develop into the embryo itself.

To evaluate the chromosomal status in human blastocysts, researchers led by Dr. Wei-Hua Wang collected 244 blastocysts from women undergoing IVF, biopsied the TE cells, and assessed all 23 pairs of chromosomes.

The results revealed by microarray indicated that 56.6% of the 244 blastocysts had an abnormal number of chromosomes. Of those, 62.3% had single and 37.7% had multiple or complex chromosomal abnormalities.


Consistent with earlier studies, blastocysts from women
aged 38 or older were found to be much more likely to
have abnormal chromosome numbers (56.4.0%)
than those from patients aged 37 or younger (43.9.2%).
Further, a mere 18% of embryos from women aged 41
and older had the correct number of chromosomes
that were deemed suitable for transplant.

When blastocysts that passed the initial inspection
were transplanted, they resulted in high pregnancy
rates (average 70.2%) independent of the
age of the mother.


After this initial assessment, the team rebiopsied 13 of the abnormal blastocysts to compare the TE and ICM cells from the same embryos using two different array platforms. Nine of the 13 blastocysts were found to be mosaic (69.23%) and, of those, four had normal ICM cells that could potentially have produced healthy offspring.

The authors therefore conclude that the commonly employed method of biopsy of TE cells alone does not predict chromosomal problems in ICM cells when there is an abnormal number of chromosomes and that older women should consider having their abnormal embryos rebiopsied if they need additional embryos for transplant.

There is clearly much left to discover in this field, and more information will be revealed as IVF clinics continue to use blastocyst microarray for embryo screening.

The article appears in the Biology of Reproduction, published by the Society for the Study of Reproduction, is a top-rated peer-reviewed research journal in the field of reproductive biology.

Liu J, Wang W, Sun X, Liu L, Jin H, Li M, Witz C, Williams D, Griffith J, Skorupski J, Haddad G, Gill J. DNA microarray reveals that high proportions of human blastocysts from women of advanced maternal age are aneuploid and mosaic. Biol Reprod 2012; (in press). Published online ahead of print 7 November 2012; DOI 10.1095/biolreprod.112.103192.

Original article: http://www.eurekalert.org/pub_releases/2012-11/sfts-nar110212.php