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The Principles of Clinical Cytogenetics - Extra Materials - Springer

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Prenatal <strong>Cytogenetics</strong> 283<br />

statistical adjustments for gestational age and maternal age. CVS procedures in which more than one<br />

attempt was made were associated with a substantially higher loss rate, supporting the observation by<br />

Silver et al. and others that increased operator experience is a key factor in assessing the risks <strong>of</strong> CVS<br />

(103). Silver’s group found that the number <strong>of</strong> placental passes and increased sample weight/aspiration<br />

attempt ratio might be more sensitive indicators <strong>of</strong> competence than the fetal loss rate.<br />

Results <strong>of</strong> a randomized international multicenter comparison <strong>of</strong> transabdominal and transcervical<br />

CVS with second-trimester amniocentesis were reported in 1991 (104). Outcome information was<br />

available for 1609 singleton pregnancies in the CVS group and 1592 in the amniocentesis group.<br />

Thirty-one centers participated, and the numbers <strong>of</strong> cases submitted ranged from 4 to 1709. Significantly<br />

fewer surviving newborns were seen in the CVS group than in the amniocentesis group (4.6%<br />

difference, p

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