Tässäpä tämä: (taulukot ja kuvat ei välttämättä tule läpi).
Kaikista raskauksista niskaturvotusta esiintyy n. 1 % sikiöistä, joista noin 20 – 25 %:lla on kromosomipoikkeavuus. Sikiöillä, joilla on poikkeava niskaturvotus on myös enemmän rakennepoikkeavuuksista, erityisesti sydänvikoja, palleahernioita, napatyriä ja luustoanomalioita. Tällä tutkimuksella löytyy n. 50 – 60 % yllämainituista kromosomipoikkeavuuksista.
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Suurin osa sikiöistä, joilta löytyy korostunut niskaturvotus, ovat täysin terveitä. Mitä suurempi turvotus on sitä suurempi riski, että jotain saattaa olla vialla.
Suurin ryhmä ovat kromosomipoikkeavuudet (riski max.n. 25%), joista Downin oireyhtymä tavallisin. Toiseksi yleisin on Turnerin oireyhtymä, jossa tyttösikiöltö puuttuu toinen X-kromosomi. Tällaisessa tapauksessa sikiöllä usein näkyy kuvaamasi lokeroinen niskahygrooma. Siitä ei kuitenkaan ollut siis kyse. Toiseksi suurin ryhmä ovat sydänviat, jotka ovat tavallisempia, jos niskaturvotus on yli 3mm, riski on n. 10%.
Valitettavasti sydän on sen verran pieni, että sitä ei päästä luotettavasti näkemäään vielä 13-14 viikolla, vaan tutkimus tehdään vasta n. 20 rvk:lla. Suurin osa sikiöistä on siis kuitenkin normaaleja. Toisaalta mikä tahansa vika voi aiheuttaa sikiön turvotusta (infektiot, aihneenvaihduntasiraudet, muut kuin sydämen rakennepoikkeavuudet jne.). Aina syytä ei saada selville tutkimuksista huolimatta.
the chances of taking home a normal baby in the presence of an increased NT is around 34% (when chromosomal structural, genetic syndromes and miscarraiges are considered together).
In a total of 22 studies involving pregnant women at high risk for having babies with chromosomal abnormalities, 30% of fetuses with increased nuchal translucency were found to have chromosomal abnormalities, and almost half of those abnormalities were Down syndrome. However, there are grave problems with the methodologies used and statistical analyses made in these studies. One recent review of the topic (Stewart & Malone, 1999) concluded: ""Results of nuchal translucency sonography are not yet sufficiently uniform to allow counseling of patients on the risk of aneuploidy [chromosomal abnormalities] based on a particular nuchal translucency thickness."" The Smith-Bindman study I mentioned above also stated: ""A thickened nuchal fold in the second trimester may be useful in distinguishing unaffected fetuses from those with Down syndrome, but the overall sensitivity of this finding is too low for it to be a practical screening test for Down syndrome.""
It is important to keep in mind that even the best combination of ultrasound findings and other variables is only predictive and not diagnostic. For true diagnosis, the chromosomes of the fetus must be examined.
If either nuchal translucency or the early blood tests are positive, this does not mean that the fetus has a chromosome problem. Approximately 4-5% of all patients having these tests have positive results and will be offered further testing such as early (12-13 week) or standard amniocentesis. Approximately 1 in 20 patients who have a positive combined test will have a Down syndrome result. Of the fetuses with normal chromosomes and slightly increased nuchal translucency most (90%) will be healthy at birth.
Patients who have a positive nuchal translucency screen and normal amniocentesis results are advised to have a level II ultrasound scan around 20 weeks. There is an increased risk for birth defects in these pregnancies. The most common associations include heart defects, mild hydrocephalus, clubfoot, and diaphragmatic hernia. Other birth defects have also been associated with positive NT screening. These can be discussed in detail with the genetic counselor.
As 1 in 70 will have heart defects a focused scan at about 20-22 weeks is recommended
Kun sikiön niskaturvotuksen paksuus on 3 mm tai enemmän, on kromosomipoikkeavuuksien todennäköisyys lisääntynyt. Todennäköisyys on noin 15-25 prosenttia. Turvotus voi johtua myös jostain muusta kehityshäiriöstä kuin Downin oireyhtymästä. Jos todennäköisyyttä laskettaessa otetaan huomioon turvotuksen paksuus, äidin ikä ja raskauden kesto, löydetään enemmän Downin oireyhtymä -sikiöitä. Jos sikiöllä todetaan tehdyn ultraäänitutkimuksen perusteella kohonnut kehityshäiriön todennäköisyys, odottavalle äidille tarjotaan mahdollisuutta osallistua sikiön kromosomitutkimukseen. Alkuraskauden jatkotutkimus on istukkanäytetutkimus. Seulonnan tarkkuus Niskaturvotusseulonnan avulla voidaan löytää noin puolet Downin oireyhtymä -sikiöistä, silloin kun käytetään rajana 3 mm turvotusta. Sikiön korostunut niskaturvotus voi kertoa myös muista kromosomipoikkeavuuksista tai kehityshäiriöistä. Tutkimuksissa voidaan löytää myös vaikeita rakennevikoja, jotka eivät johdu kromosomipoikkeavuudesta. Suurin osa sikiöistä, joilla ultraäänitutkimuksessa on havaittu lisääntynyttä turvotusta, todetaan jatkotutkimuksissa normaaleiksi. Tärkeää Ennen tutkimukseen osallistumista on tärkeää ymmärtää, että vaikka sikiöllä ei todettaisi lisääntynyttä niskaturvotusta, sikiöllä voi siitä huolimatta olla jokin kehityshäiriö. Sikiöllä voidaan myös todeta lisääntynyttä niskaturvotusta, vaikka mitään kehityshäiriötä ei olisikaan. Tutkimus kertoo vain kohonneesta poikkeavuuden todennäköisyydestä. Excess nuchal translucency is defined as an abnormal collection of fluid under the skin at the back of the fetus' neck.
In the majority of cases, the fluid disappears and has no effect on the baby. However, abnormal nuchal translucency is an ultrasound “marker”, which indicates increased risk for certain problems.Approximately 10-15% of babies who demonstrate excess nuchal translucency on ultrasound may have an associated chromosome abnormality, particularly Down syndrome or Turner syndrome . Chromosome abnormalities involving a missing or extra chromosome are not usually inherited and are not caused by an exposure during pregnancy. Instead, they are caused by random events in cell division at the time of conception and can occur in anyone’s pregnancy. Prenatal diagnosis by CVS or amniocentesis is available to test for these chromosome abnormalities during pregnancy. Excess nuchal translucency has also been associated with an approximate 15% risk for a defect of the heart or skeleton. A detailed ultrasound performed at 18-20 weeks can help identify these birth defects. A specialized ultrasound , called an echocardiogram, is used to look specifically at the structure of the heart. Babies with excess nuchal translucency are also at increased risk to be affected with certain genetic syndromes caused by gene changes (mutations). It is important to remember that excess nuchal translucency may be a normal variant in a baby and cause no health problems. The mother's age-related risk of a chromosomal disorder in the unborn child increases in relation to the thickness of the nuchal translucency. If the latter is 3 mm, the risk is threefold, at 4mm it is 18-fold, at 5 mm it is 28-fold, when the thickness exceeds 5 mm, the risk is 36-fold, when less than 3 mm, the risk is decreased three-fold. In 3 % to 5 % of all pregnancies the nuchal translucency is distended, irrespective of the mother's age. As of a thickness of 3.0 mm, there is a steady rise in the probability of a chromosomal disorder (Table 1). This makes it a relatively reliable marker (approximately 80 %), providing useful information when consulting the expectant mother. Nuchal translucency in mm < 2,0 2,0 - 2,9 3,0 - 3,9 4,0 - 4,9 5,0 - 5,9 6,0 - 6,9 > 6,9
chromosomal dis-orders in % 0,3 3,2 14,3 45,5 28,6 75,0 100
Table 1 Nuchal translucency and probability of a chromosomal disorder irrespective of the mother's age (Frauenklinik Klinikum Darmstadt, examination of 1119 pregnancies) If a scan verifies a nuchal translucency exceeding 3 mm, we recommend a diagnostic method to exclude possible chromosomal disorders (see Chapter IV.). Studies carried out in recent years have provided evidence of a connection between the presence of nuchal translucency and the occurrence of cardiac deficiencies, diaphragmatic defects, defects of the abdominal wall and anomalies in the kidneys, independently of the chromosome complement. In the presence of nuchal thickening, the probability of such complications rises fivefold in comparison to norm groups. In the event of congenital cardiac defects, nuchal thickening (distended nuchal translucency) in the first trimester is presumed to be connected to the reduced cardiac ejection performance present in such cases, as well as to anomalies in venous drainage. The same applies to diaphragmatic defects, where the organs of the abdominal cavity are displaced into the chest, thereby exerting a negative influence on the position and function of the heart. Thus, when the nuchal translucency exceeds 3 mm, the foetus should be examined for a cardiac defect in a specialised clinic in weeks 22/23, irrespective of a normal chromosome complement.Objective: One of the concerns of prenatal diagnosis is to find sensitive markers to screen for chromosome abnormalities, such as serum assays or nuchal translucency (NT). This study reports our experience with NT measurement during the first trimester of pregnancy. Materials: The study was performed prospectively on 252 fetuses with either NT 3 mm or cystic hygroma. Results: We observed 50 abnormal karyotypes, i.e. 19.8%. The incidence of chromosome abnormalities increased with increasing maternal age and increasing NT thickness. For the 202 fetuses with normal karyotypes, outcome was unfavourable in 32 cases: 23 elective terminations of pregnancy, 8 spontaneous abortions and 1 neonatal death. Outcome was favourable in 141 cases. Twenty-nine pregnancies were lost to follow-up. Conclusion: Measurement of NT at 12 weeks' gestation seems to be a good marker for chromosome abnormalities. When the karyotype is normal, the pregnancy outcome remains correlated with the degree of NT thickness. The finding of NT >3 mm between 10 and 14 weeks' gestation dictates rigorous ultrasound monitoring and caution when predicting pregnancy outcome.The inaccuracy of screening tests means that there is an unavoidable down side. Not all affected babies will be identified, and many mothers carrying unaffected babies will have the unnecessary worry of a “positive” result. With nuchal translucency, for example,19 out of 20 women who get a “positive” result will not be carrying an affected baby, but will go through counselling and amniocentesis (with a 1 in 200 risk of causing miscarriage), then wait days to weeks before reassuring results are back.
