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8. What about chorionic villus sampling (CVS) as an alternative to amnio?




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This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (gazissax@netcom.com) with numerous contributions by others.

8. What about chorionic villus sampling (CVS) as an alternative to amnio?

Chorionic villus sampling is an early surgical test in which part of the
chorion, the outer tissue of the sac surrounding the embryo, is removed
and analyzed. It is a newer test than amniocentesis, and is still
considered experimental. The chief advantage of CVS over amnio is that
the results are available much more quickly. CVS is done between the
ninth and twelfth week of pregnancy, and the results are available within
ten days.

As of 1989, ACOG no longer considers CVS experimental (March of Dimes)

The disadvantages of CVS are, first, that it does not detect neural tube
defects, as amnio does. Second, there may be some missed diagnoses due to
chorionic mosaicism. Third, there is a higher risk of miscarriage. There
are various estimates for this risk: 1% to amnio's 0.5% (ACOG), 1-5%
compared to .2% for amnio (Blatt), and others simply say that the safety
and long term effects of CVS are unknown. There is some evidence that CVS
may sometimes cause limb defects, but this evidence is inconclusive.

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From Robert Brenner, MD:

CVS(Chorionic villus sampling) is a procedure where a piece of the
placenta is aspirated into a plastic tube and cultured for chromosome
analysis. There are case reports of abnormal limb development following
CVS but this is thought to be avoided if CVS is done after 8 weeks
gestation. The pregnancy loss rate is higher than amniocentesis but the
backround loss at 10 weeks is higher also. The advantage of CVS is that a
diagnosis of chromosomal abnormality can be made earlier enabling a
patient to terminate her pregnancy by D&C rather than by prostaglandin
urea induction of labor as is done later in pregnancy (after
amniocentesis).
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More information on the limb defects: A study by the Centers for Disease
Control and Prevention, in 1994, found that infants whose mothers had
CVS had a 0.03% chance of missing or underdeveloped fingers or toes.
The normal risk is about 0.005%. Some researchers have said that this
study was poorly done and looked at too few births. Dr. Laird Jackson
of Thomas Jefferson University in Philadelphia said that he had followed
about 120,000 women who had CVS and found no such increase. A 1992
survey by WHO found miscarriage rates of from 1.2%-8.4% at different
medical centers worldwide (there is apparently a lot of variation in
miscarriage rates from one center to another), and a slight increase in
fetal limb defects, from 5.4 cases per 10,000 to 6 per 10,000. A study
published in the August, 1992 issue of the New England Journal of Medicine
found a 0.8% greater chance of miscarriage. More details can be found
in newspaper articles in the New York Times on March 12, 1994, July 15,
1994, and October 23, 1994, and in the article "Prenatal Diagnosis,"
in the New England Journal of Medicine, by Alton and DeCherney.


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From Dr. T. Reynolds:

One other interesting development which applies to some couples only is
polymerase chain reaction DNA testing: One case has been reported where
the husband had a Haemoglobinopathy (sickle-cell-type disorder) called
Haemoglobin Lepore-Boston (OK so its rather rare, but it's an example of what
can be done). A similar technique can be used to diagnose fetal sex from a
maternalblood sample if it is likely to be clinically important (e.g. for
avoidance of muscular dystrophy/other sex linked disorders). NOTE: some of
these techniques may only be available in big research centres.
-----------------------------------------


Sources:

Alton and DeCherney. "Prenatal Diagnosis." New England Journal of
Medicine. January 14, 1993.

The American College of Obstetricians and Gynecologists (abbreviated in
references as ACOG). Planning for Pregnancy, Birth, and Beyond. A
Dutton Book, May, 1992.

Blatt, Robin J.R. Prenatal Tests. Vintage Books. New York, August 1988.

The Boston Women's Health Collective. The New Our Bodies, Our Selves.
Simon and Schuster. New York, NY, 1992.

Rothman, Barbara Katz. The Tentative Pregnancy. Viking Penguin Inc. New
York, NY, 1986.

Scher, Jonathan, M.D., and Dix, Carol. Will My Baby Be Normal? How to
Make Sure. The Dial Press. New York. 1983.









 

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