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RETIRED: Prenatal Screening for Fetal Aneuploidy

2007; Elsevier BV; Volume: 29; Issue: 2 Linguagem: Inglês

10.1016/s1701-2163(16)32379-9

2665-9867

Anne Summers, Sylvie Langlois, Phil Wyatt, R. Douglas Wilson, R. Douglas Wilson, Victoria M. Allen, Claire Blight, Valérie Désilets, Alain Gagnon, Jo‐Ann Johnson, Sylvie Langlois, Anne Summers, Phil Wyatt, Sylvie Langlois, David Chitayat, Albert E. Chudley, Sandra A. Farrell, Michael T. Geraghty, Chumei Li, Sarah M. Nikkel, Andrea Shugar, Anne Summers, Frédérique Tihy, Lucie Morin, Michael Van den Hof, Stephen Bly, Robert Gagnon, Barbara Lewthwaite, Yvonne Cargill, Kenneth Lim, Annie Ouellet,

Fetal and Pediatric Neurological Disorders

To develop a Canadian consensus document withrecommendations on maternal screening for fetal aneuploidy(e.g., Down syndrome and trisomy 18) in pregnancy. Pregnancy screening for fetal aneuploidy started in the mid1960s, using maternal age as the screening test. Newdevelopments in maternal serum and ultrasound screening havemade it possible to offer all pregnant patients a non-invasivescreening test to assess their risk of having a fetus with Downsyndrome or trisomy18 to determine whether invasive prenataldiagnosis tests are necessary. This document will review theoptions available for non-invasive screening and makerecommendations for Canadian patients and health care workers. To offer non-invasive screening for Down syndrome ortrisomy 18 to all pregnant women. Invasive prenatal diagnosiswould be limited to women who screen above a set risk cut-offlevel on non-invasive screening or pregnant women who will be 40years at time of delivery who, after counselling, chose to go directlyto amniocentesis/chorionic villi sampling (CVS). Currently availablenon-invasive screening options include maternal age combined with (1) first trimester screening (FTS) (nuchal translucency,maternal serum biochemical markers); (2) second trimester serumscreening; or (3) two-step integrated screening, which includes firstand second trimester serum screening with or without nuchaltranslucency (IPS, Serum IPS, contingent and sequential). Theseoptions are reviewed and recommendations are made. A MEDLINE search was carried out to identify papersrelated to this topic that were published between 1982 and 2006.Practices across Canada were surveyed. A consensus documentwas drafted and reviewed by committee members. The quality of evidence and classification ofrecommendations followed discussion and consensus by thecombined committees of SOGC (Genetics, Diagnostic Imaging)and CCMG (Prenatal Diagnosis). These guidelines are intended to reduce thenumber of amniocenteses done when maternal age is the onlyindication. This will have the benefit of reducing the numbers ofnormal pregnancies lost because of complications of invasiveprocedures. Any screening test has an inherent false positive rate,which may result in undue anxiety. A detailed cost-benefit analysisof the implementation of this guideline has not been done, sincethis would require health surveillance and research and healthresources not presently available; however, these factors need tobe evaluated in a prospective approach by provincial and territorialinitiatives. Recommendations All pregnant women in Canada, regardless of age, should beoffered, through an informed consent process, a prenatalscreening test for the most common clinically significant fetalaneuploidies in addition to a second trimester ultrasound fordating, growth, and anomalies. (I-A) Maternal age screening is a poor minimum standard for prenatalscreening for aneuploidy and should be removed as an indicationfor invasive testing. Amniocentesis/chorionic villi sampling (CVS)should not be provided without multiple marker screening resultsexcept for women over the age of 40. Patients should becounselled accordingly. (I-A) In 2007, as a minimum standard, any prenatal screen offered toCanadian women should have a 75% detection rate with no morethan a 5% false positive rate for Down syndrome. The performanceof the screen should be substantiated by annual audit. (III-B) First trimester nuchal translucency should be interpreted for riskassessment only when performed by sonographers/sonologiststrained and accredited to provide this service and with ongoingquality assurance. (II-2A) It should not be offered as a screenwithout biochemical markers except in the context of multiplegestation pregnancies. (I-A) For women who undertake first trimester screening (FTS), secondtrimester serum alpha fetoprotein (AFP) screening and/orultrasound examination is recommended to screen for open neuraltube defect (ONTD). (II-1A) First trimester screening (FTS), the first step of integratedscreening (with or without nuchal translucency), contingent, andsequential screening are performed in an early and relativelynarrow time window. Timely referral is critical to ensure women areable to undergo the type of screening test they have chosen. (II-1A) Soft markers or anomalies in the 18- to 20-week ultrasound can beused to modify the a priori risk of aneuploidy established by age orprior screening provided the scan is undertaken in an establishedcentre performing tertiary level ultrasound. In the absence ofultrasound soft markers or anomalies, a negative likelihood ratio of0.5 should be used. (II-2B) Evaluation of the fetal nasal bone in thefirst trimester remains technically difficult and should not beincorporated as a screen until locally established as an effectiverisk assessment tool. (III-D) Health care providers should be aware of the screening modalitiesavailable in their province or territory. (III-B) Screening programs should be implemented with resources thatsupport audited screening and diagnostic laboratory services,ultrasound, genetic counselling services, patient and health careprovider education, and high quality diagnostic testing, as well asresources for administration, annual clinical audit, and datamanagement. In addition, there must be the flexibility and fundingto adjust the program to new technology and protocols. (II-3B) Screening programs should show respect for the needs and qualityof life of persons with disabilities. Counselling should benondirective and should respect a woman's choice to accept or torefuse any or all of the testing or options offered at any point in theprocess. (III-I) By 2008, screening programs should aim to provide a screen that,as a minimum, offers women who present in first trimester adetection rate of 75% for Down syndrome, with no more than a 3%false positive rate. (III-B)