December 19, 2011
Wishing all our patients, past and present, a very Happy Christmas and warm wishes for a wonderful new year in 2012
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December 05, 2011
Before you reach for 'just the one' coffee to keep you going whilst doing your Christmas shopping, it might be worth looking at a new study and then deciding on ...
November 30, 2011
A new study of where babies are born was recently conducted - and they didn't mean whether it was in Cardiff or Swansea, but whether they were born in hospital, ...
Various tests have been developed to try to identify those women at greatest risk of having a chromosomally abnormal baby such as Down's Syndrome, who could then decide whether or not to proceed to amniocentesis. The TripleTest or Barts Test at about 15 weeks into the pregnancy detects about 70% of Down's Syndrome pregnancies based on about 1 in every 25 (4%) women having the blood test ending up with a high risk result (i.e more than 1 in 150 at term) and then proceeding to amniocentesis. This means it misses 1 Downs Baby for every 2 it picks up! It cannot identify pregnancies at increased risk of Trisomy 18 (Edward Syndrome) or Trisomy 13 (Patau Syndrome).
The test is less efficient in younger women with a detection rate of only about 30% and in women over 35 there is a high likelihood that testing will place them in a high risk category warranting amniocentesis. This means unecessary amniocentesis procedures and miscarriages which could have been avoided. This has been highlighted in a recent article in the Guardain.
The blood test is not done until 15 weeks and therefore decisions about amniocentesis are made at 16 weeks with final results and decisions about the pregnancy made at 18 weeks. At this late stage the woman can feel the baby's movements and the pregnancy is almost half way through. If termination is considered for an abnormal result it is usually by a medically induced birth, which may mean up to 2 to 3 days in hospital.
The test is not valid for women with multiple pregnancy and cannot be relied upon in women who have had a previous baby with a chromosomal abnormality such as the common type of Down’s Syndrome (Trisomy 21).
If all is well then the woman will have had to wait until nearly 18 weeks into the pregnancy to have the reassurance that the baby does not have Down’s Syndrome if her blood test shows a high risk result.
The risk of Down Syndrome increases with advancing maternal age but about half of babies with Down Syndrome are in mothers under 35 years old and therefore ALL women should consider having a screening test.
Maternal Age Risk of Down Syndrome
Maternal Age at term
Risk of Down Syndrome
20
1:1450
21
22
23
1:1400
24
25
1:1350
26
1:1300
27
1:1200
28
1:1150
29
1:1050
30
1:940
31
1:820
32
1:700
33
1:570
34
1:460
35
1:350
36
1:270
37
1:200
38
1:150
39
1:110
40
1:85
41
1:70
42
1:55
43
1:45
44
1:40
45
1:35
46
1:30
47
48
49
50
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