The probability of chromosomal and other anomalies and fetal and postnatal death increases with nuchal translucency thickness. The combined first trimester test identifies factors that are known to be associated with fetal chromosomal anomalies and that are independent of each other. Offering testing for probability of fetal chromosomal anomaly to all women in the first trimester, regardless of maternal age, is recommended in the United Kingdom ( NICE 2008), the United States ACOG 2007 and Australia RANZCOG 2015. In the first trimester, give all women/couples information about the purpose and implications of testing for probability of chromosomal anomalies to enable them to make informed choices.Īpproved by NHMRC in December 2011 expires December 2016 50.2 Effectiveness of tests for probability of chromosomal anomaly As cf DNA testing can be performed at any gestation from 10 weeks, it should be discussed along with second trimester serum screening for women who have missed the gestational age window for combined first trimester screening. While this is an important publicly funded option for women who present later in pregnancy or for whom specialist ultrasound is not available (eg in rural and remote areas) or who cannot afford cf DNA testing (until this becomes publicly funded), the evidence for these tests has not been reviewed as part of the development of these Guidelines.
#AFP TEST DONE SECOND SEQUENTIAL SCREENING FREE#
Later in pregnancy (14 to 20 weeks), the triple test (maternal serum testing of a-fetoprotein, free β- hCG and unconjugated estriol) or the quadruple test (which also includes inhibin A) is used to assess the risk of fetal chromosomal anomaly. Use of cf DNA as a first-tier test may be appropriate for women with infections where an invasive procedure carries an increased risk of mother-to-child transmission. Evaluations of the implementation of contingent cf DNA testing in national screening programs have found improved performance of the program Chitty et al 2016, Gil et al 2016, Oepkes et al 2016. If the fetus is affected by trisomy, a greater than expected number of the relevant chromosome fragments will be present in maternal serum.Ĭell-free DNA testing has been used as a first-tier test, as a second-tier test (with women with increased probability on combined first trimester screening offered cf DNA or diagnostic testing) or in a contingent model (where women with an intermediate probability on combined first trimester screening are offered cf DNA testing and those with a very high probability are offered diagnostic testing).
The test involves sequencing DNA fragments in maternal serum, mapping each DNA sequence to a reference genome to determine its chromosome of origin, and counting the number of fragments arising from each chromosome. cf DNA testing can be performed for detection of fetal anomaly from 10 weeks gestation. maternal plasma testing of pregnancy-associated placental protein-A ( PA PP-A) and free beta-human chorionic gonadotrophin ( β- hCG) between 9 weeks and 13 weeks, 6 days gestation.Īn emerging practice is the use of cell-free deoxyribonucleic acid ( cf DNA) testing (also referred to as non-invasive prenatal testing ).ultrasound measurement of fetal nuchal translucency thickness between 11 weeks and 13 weeks 6 days gestation (when the fetus has a crown-rump length of 45–84 mm) combined with.
The combined first trimester test comprises: Extensive pre- and post-test information and counselling are required, with consideration also being given to the woman’s preferences, availability of testing facilities, costs to the woman and, for ultrasound, operator expertise.Ĭurrent practice in Australia is that testing for chromosomal anomalies is done in the first trimester. The suitability of any test depends on the gestational stage. A high probability test result leads to the offer of a diagnostic test (chorionic villus sampling or amniocentesis) ( see Chapter 51). On this page 50.1 Approaches to testing for high probability of chromosomal anomaliesĪ range of biochemical tests and ultrasound techniques has been developed that can significantly increase the identification of pregnancies with a high probability of chromosomal anomalies such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) ( see Glossary).
0 kommentar(er)
