vajiheh marsoosi, m.d associate professor of tums shariati hospital
TRANSCRIPT
Vajiheh Marsoosi, M.D
Associate Professor of TUMS
Shariati Hospital
Trisomic Pregnancies are associated with altered maternal
serum concentration of various feto-placental products.
Screening in the first trimester by a combination of
maternal age, fetal NT, and serum free ß-hCG and PAPP-A
identifies about 90% of trisomy 21 pregnancies for a false
positive rate of 3%.
In trisomy 21 pregnancies
maternal serum free ß-hCG
is about twice as high and
PAPP-A is reduced to about
half compared to
chromosomally normal
pregnancies.
Adjustment is necessary in the
measured free ß-hCG and PAPP-A
Each measured level is first
converted to a multiple of the
expected normal medium (MoM)
specific to the same gestation,
maternal weight, smoking status,
ethnicity and method of conception.
In Black women the PAPP-A level is about
60% higher than in White women.
In women who smoke and those
conceiving by IVF serum PAPP-A is
decreased and this could increase in false
positive rates.
In trisomy 21 pregnancies: Free ß-hCG is higher than in euploid
pregnancies and the difference between the two
is higher at 13 than at 11 weeks.
Serum PAPP-A is lower than in euploid
pregnancies and the difference the two is
higher at 11 than at 13 weeks.
The difference from euploid pregnancies in
PAPP-A at 11 weeks is greater than the
difference in ß-hCG at 13 weeks and therefore
the overall performance of biochemical
markers is better at 11 than at 13 weeks.
In trisomy 21compared to euploid pregnancies:
The difference in biochemical markers is greater at 11 than
at 13 weeks.
The difference in fetal NT is greater at 11 than at 13 weeks.
Therefore the overall performance of screening is better at
11 than at 13 weeks.
The overall performance of combined screening is better
at 11 than at 13 weeks and may be best at 10 weeks.
Ultrasound screening for fetal abnormalities is better at 12
than at 11 weeks and much better than at 10 weeks.
A good way of achieving a high performance of screening
for trisomy 21 and diagnosing major fetal defects by
ultrasound is to carry out the blood test at 10 or 11 weeks
and the ultrasound scan at 12 weeks.
Other defectsIn euploid pregnancies the average free ß-hCG is 1.0 MoM and
PAPP-A is 1.0 MoMIn chromosomal defects the values are: free ß-hCG PAPP-A Trisomy 21 2.0 0.5 Trisomy 18 0.2 0.2 Trisomy 13 0.3 0.4 Turner 1.2 0.5 Triploidy Digenic 0.2 0.1 Diandric 9.0 0.7
Other defects There are differences between the three
trisomies: Fetal NT is higher in T18 and T 13 than
T21 Serum free ß-hCG in trisomy 21 is high
whereas in trisomies18 and 13 this is low
Serum PAPP-A is lower in trisomies18 than in trisomy 21
Fetal heart rate in trisomy 13, unlike trisomies 21 and 18, is high