From: Subject: Patient Information Leaflet Date: Fri, 1 Apr 2005 13:26:55 +0200 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0018_01C536BE.7900D130" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0018_01C536BE.7900D130 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.fetalmedicine.com/patient_info.htm Patient Information Leaflet

Patient Information

First trimester screening for Downs syndrome

The vast majority of babies are healthy, but about 1 in = 100 are=20 born with a serious mental or physical handicap. One of the=20 commonest conditions is Downs syndrome, when the baby = receives an=20 extra chromosome 21 (Trisomy 21). It is more common with = older=20 mothers, but can occur whatever the age of the mother (see = the table=20 below).

Maternal age (yrs)

Chance of Downs = syndrome

At 12 weeks

At birth

20

1 in 1070

1 in 1530

25

1 in 950

1 in 1350

30

1 in 630

1 in 900

32

1 in 460

1 in 660

34

1 in 310

1 in 450

35

1 in 250

1 in 360

36

1 in 200

1 in 280

38

1 in 120

1 in 170

40

1 in 70

1 in 100

42

1 in 40

1 in 55

44

1 in 20

1 in = 30

Screening for Downs syndrome and diagnostic testing =

The only way to be certain whether the fetus has Downs = syndrome=20 or not is by doing a diagnostic test =96 an amniocentesis or = chorionic=20 villus sampling (CVS). A CVS is performed between 11 and=20 13+6 weeks and involves taking a small amount of = tissue=20 from the placenta; an amniocentesis involves taking fluid = from=20 around the baby and is usually done after 15 weeks. Both = provide a=20 sample that contains tissue that has the same genetic = make-up as the=20 baby and will allow the baby=92s chromosomes to be looked at = in=20 detail. But the problem with these invasive tests is that = they can=20 cause a miscarriage, even if the baby is entirely normal. = The risk=20 of miscarriage is about 1%.

Therefore the decision as to whether to have an invasive = test or=20 not must be taken on the basis of a non-invasive assessment = of the=20 likelihood (risk) that the baby has Downs syndrome. The most = accurate way of estimating this risk is by combining the = information=20 from:

  • The age of the mother=20
  • The findings from an ultrasound scan at = 11-13+6=20 weeks (the nuchal translucency scan)=20
  • Information obtained from the levels of certain = pregnancy=20 hormones in the mother=92s blood.

The nuchal scan

The nuchal scan is an ultrasound scan performed between = 11 and=20 13+6 weeks of pregnancy, during which the fluid = at the=20 back of the baby=92s neck (the nuchal translucency) is = measured. All=20 babies will have some fluid here, but in babies with Downs = syndrome=20 the fluid tends to be increased.

What else does the scan do?

Other things that we can do at the time of the scan = are:

  • Confirm your dates=20
  • Check that the baby is developing normally=20
  • Diagnose a multiple pregnancy=20
  • Check the fetal anatomy that is visible at this stage =

First trimester serum biochemistry

A blood test taken from the mother can be used to measure = the=20 levels of two hormones (free =DF-hCG and PAPP-A). In = pregnancies=20 affected by Downs syndrome there is a tendency for the = levels of=20 free =DF-hCG to be increased and PAPP-A to be decreased.

The combined first trimester screening test

  • Screening by maternal age alone picks up about 30% of = the=20 babies with Downs syndrome.=20
  • Screening by nuchal translucency picks up about 80% of = the=20 babies with Downs syndrome.=20
  • Screening by free =DF-hCG and PAPP-A picks up about = 60% of the=20 babies with Downs syndrome.=20
  • The combination of these three methods is the most = effective,=20 picking up about 90% of the babies with Downs syndrome. =

At the end of the combined screening test you will be = given a=20 risk that the baby has Downs syndrome; it will not tell you=20 definitely whether or not your baby has Downs syndrome, but = can be=20 used to help you to make an informed choice about whether to = have an=20 invasive test. The wish to proceed to one is a purely = personal=20 decision, but as a guide we normally offer an invasive test = if the=20 risk of Downs syndrome is 1 in 300 or worse. This of course = means,=20 that even with a high-risk result most women will still have = a=20 completely normal baby.

The 20 week scan

The best way to detect structural problems, including = spina=20 bifida, is a scan at 18 - 23 weeks and, whatever your nuchal = scan=20 shows, it is recommended that you have this scan to check = the=20 structure of the baby in more detail.

If the nuchal measurement is increased we recommend a = detailed=20 heart scan too, because a heart abnormality can be the cause = of the=20 increased nuchal fluid.

After you have delivered

Please help us by returning the outcome of pregnancy form = once=20 you have delivered your baby, so that we can monitor our = service. We=20 are always looking for ways to improve our service too and = welcome=20 any comments or feedback you may have.

Further questions

Please feel free to discuss in more detail any of the = issues=20 raised in this section at the time of your=20 scan.

 
 
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