Prenatal Screening for and Diagnosis of Aneuploidy in Twin Pregnancies

Objective: To provide a Canadian consensus document with recommendations on prenatal screening for and diagnosis of fetal aneuploidy (e .g ., Down syndrome and trisomy 18) in twin pregnancies . Options: The process of prenatal screening and diagnosis in twin pregnancies is complex . This document reviews the options available to pregnant women and the challenges specific to screening and diagnosis in a twin pregnancy . Outcomes: Clinicians will be better informed about the accuracy of different screening options in twin pregnancies and about techniques of invasive prenatal diagnosis in twins . Evidence: PubMed and Cochrane Database were searched for relevant English and French language articles published between 1985 and 2010, using appropriate controlled vocabulary and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health risk, genetic health surveillance, prenatal diagnosis, twin gestation) . Results were restricted to systematic reviews, randomized controlled trials, and relevant observational studies . Searches were updated on a regular basis and incorporated in the guideline to August 2010 . Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies . The No. 262 (Replaces No. 187, February 2007) This document reflects emerging clinical and scientific advances on the date issued and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed. Local institutions can dictate amendments to these opinions. They should be well documented if modified at the local level. None of these contents may be reproduced in any form without prior written permission of the SOGC. This clinical practice guideline has been prepared by the Genetics Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and the Prenatal Diagnosis Committee of the Canadian College of Medical Geneticists (CCMG) and approved by the Executive and Council of the Society of Obstetricians and Gynaecologists of Canada and the Board of Directors of the Canadian College of Medical Geneticists.