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Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: large scale validity study

BMJ 2011; 342 doi: (Published 11 January 2011) Cite this as: BMJ 2011;342:c7401

The Risk of Amniocentesis and CVS is clearly overstimated

Despite the importance and the advantages of the non-invasive
prenatal diagnosis, the risks of Amniocentesis and CVS are clearly and
surprisingly overestimated in the article of Chu RWK, et. al.(1)

The pregnancy loss rate after midtrimester amniocentesis has been usually
quoted to be approximately 0.5%. This risk was derived from three studies
in the United States (2), Canada (3), and Great Britain (4) performed in
the 1970s, who were performed in a time when ultrasound guidance for
amniocentesis was not routine, and the clarity of ultrasound in the 1970s
was relatively poor.

Chu RWK, et al give a risk of 1% quoting a study by Tabor A et al from
1986(5), this study had unexpectedly low background loss rate in the non-
amniocentesis group, and other concerns.

A 2006 study (6)with total of 35,003 unselected patients from the general
population with viable singleton pregnancies Patients who either did
(3,096) or did not (31,907) undergo midtrimester amniocentesis were
identified. They found evidence that the real added miscarriage risk of
amniocentesis is only be 0.06% -- which equates to 1 in 1,600.
miscarriages that occurred after an amniocentesis might not be
attributable to the procedure itself.

After that study, the Washington University School of Medicine analyzed
its own information from 1990 to 2006 and found that the increased risk of
miscarriage after an amniocentesis was only 0.13% -- 0.97% of women who
had an amniocentesis before 24 weeks had a spontaneous late miscarriage
or preterm birth, but this also happened in 0.84% of women who did not
have an amniocentesis. They concluded that the difference was not
statistically significant.

Many obstetricians and geneticist agree that the traditionally quoted risk
of 0.5% for amniocentesis is an overestimate, but Non-invasive prenatal
assessment of aneuploidies will be a welcome development.

1. Chiu RWK, et al Non-invasive prenatal assessment of trisomy 21 by
multiplexed maternal plasma DNA sequencing: large scale validity study.BMJ
2011:342:c7401. doi:10.1136

2. Midtrimester amniocentesis for prenatal diagnosis. Safety and accuracy.
JAMA 1976;236:1471-6.

3. Simpson NE, Dallaire L, Miller JR, Siminovich L, Hamerton JL, Miller J,
et al. Prenatal diagnosis of genetic disease in Canada: report of a
collaborative study. Can Med Assoc J 1976;115:739-48.

4. An assessment of the hazards of amniocentesis. Report to the Medical
Research Council by their Working Party on Amniocentesis. Br J Obstet
Gynaecol 1978;85 suppl:1-41.

5. Tabor A, Philip J, Madsen M, Bang J, Obel EB, Norgaard-Pedersen B.
Randomised controlled trial of genetic amniocentesis in 4606 low-risk
women. Lancet 1986;1:1287-93.

6. Eddleman KA, et. al. Pregnancy Loss Rates After Midtrimester
Amniocentesis. Obstetrics & Gynecology. 2006. 108,5,pp 1067-1072
doi: 10.1097/01.AOG.0000240135.13594.07

7. Kuehn BM. Study Downgrades Amniocentesis Risk. JAMA. 2006;296(22):2663-
2664. doi: 10.1001/jama.296.22.2663

Competing interests: No competing interests

14 January 2011
Carlos Trujillo
Erfan General Hospital, Jeddah, Saudi Arabia