is a term used to describe a chromosome problem, that is
caused by an extra or missing chromosome. If an error occurs
leading to the egg or sperm having an extra or missing
chromosome, the embryo created by that egg or sperm would
have an extra or missing chromosome. This situation is
called aneuploidy. Having an extra chromosome is known as
trisomy (tri = three of the chromosome) and having a
chromosome missing is known as monosomy (mono = one of the
The most common chromosome abnormalities in miscarriages
include: trisomy (3 copies of a chromosome) or monosomy (one
copy of a chromosome) for chromosomes 13, 15, 16, 18, 21, or
22; triploidy (3 copies of all the chromosomes); and
abnormalities of the sex chromosomes.
The most common example of a chromosomal aneuploidy is Down
syndrome, or trisomy 21. Other common chromosomal
aneuploidies are trisomy 13, trisomy 18, Turner syndrome and
Klinefelter syndrome, which can result in liveborn children
with a range of birth defects and cognitive disability.
? Down syndrome is caused by an extra copy of chromosome 21
and is also known as trisomy 21. Down syndrome is associated
with mental retardation and other birth defects, such as
? Turner syndrome is caused by the absence of one sex
chromosome, also known as 45,XO. Approximately 99% of
pregnancies affected with Turner syndrome are miscarried.
? Trisomy 18 is due to the presence of an extra copy of
chromosome 18 in the baby?s cells. The risk for miscarriage
in the pregnancy is increased. Babies born with trisomy 18
have severe mental retardation and other birth defects. The
majority of babies do not survive beyond the first few
months of life.
? Trisomy 13 is due to the presence of an extra copy of
chromosome 13 in the baby?s cells. This condition is similar
to trisomy 18 in its severity and outcome.
We also test for chromosomes 8, 9, 15, 16, 17, and 22.
Aneuploidy conditions involving these chromosomes can cause
lack of implantation or can results in a miscarriage early
is known that approximately 3 out of 4 (75%) embryos created
by IVF will not be capable of producing a live born child.
Some will fail to implant in the uterus, while others will
implant but be unable to carry out early embryonic
development. Finally, as in natural pregnancy, approximately
15%-20% of conceptions will be lost as a clinical
miscarriage. While there are many reasons for the failure of
an embryo to make a baby, the single most important factor
is an abnormality of the chromosomes.
Similarly, for most couples, a significant number of the
embryos created by IVF will have chromosome abnormalities.
The exact percentage of chromosomally abnormal embryos that
each couple produces is related to many factors including
maternal age, number of failed IVF cycles, and the type of
sperm used. In addition, a certain percentage of
abnormalities are due to the fact that IVF is not a natural
process, and hyperstimulation of the ovaries produces an
increased percentage of chromosomally abnormal eggs.
Risk of Aneuploidy and maternal age