In reply to the second part of this post, first trimester screening is
generally claimed to provide about 15-20% extra detection; but this is at a
time when proportions of affected are higher - so after correction for
spontaneous losses the two detection rates are approximately the same.
TIM
****************************************************************************
*********
Prof. Tim Reynolds,
Clinical Chemistry Department,
Queens Hospital,
Belvedere Rd.,
Burton-on-Trent,
STAFFORDSHIRE,
DE13 0RB,
UK.
tel: 01283 511511 ext. 4035
fax: 01283 593064
email: [log in to unmask]
alternative email for the all too frequent occasions when the NHS email
connection doesn't work:
[log in to unmask]
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-----Original Message-----
From: Bruce Campbell [mailto:[log in to unmask]]
Sent: 24 September 2002 01:59
To: [log in to unmask]
Subject: Reporting risks in first trimester Downs screening
I am interested in laboratory policy regarding reporting risk(s) in
combined maternal serum biochemistry and NT Downs risk screening. It is
possible to calculate three risks if combined screening is done: from
biochemistry alone, from NT alone and the combined risk. My personal view
at present is that it is best to report only the combined risk, even if the
biochemistry is done early e.g. at 10 weeks and the NT scan not until 12
weeks. I would particularly like to hear from anyone who disagrees and
feels that patients should be given the maternal serum biochemistry risk
separately and their reasons for doing this.
A second question. Both first and second trimester maternal serum
biochemistry testing are reported to give similar Down syndrome detection
rates of about 65%. Since the proportion of affected fetuses that will
undergo spontaneous fetal loss is higher in the first trimester, the
reported detection rates are not directly comparable. The first trimester
detection rate needs to be adjusted down by 8 - 10% to compensate for this
effect. This means that second trimester biochemistry alone is better than
first trimester biochemistry alone in Down syndrome detection. NTD
detection is another issue. Is this argument correct or incorrect?
Thanks in advance for any assistance.
Bruce Campbell
****************************************
Bruce Campbell FRCPA FAACB
Sullivan Nicolaides Pathology
Ph 61 (0)7 3377 8672
Fax 61 (0)7 3870 5989
Email [log in to unmask]
****************************************
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