Down syndrome screening in assisted conception twins: An iatrogenic medical challenge

OBJECTIVE: The objective of this study was to provide a critical analysis of the impact of assisted conception on prenatal screening for Down syndrome (DS) in twin pregnancies and the value of various screening modalities for early detection of anomalies. METHODS: The literature was searched using PubMed and the Cochrane Library focusing on prenatal screening and antenatal care of assisted-conception twin pregnancies. RESULTS: Serum screening alone is of limited value in detecting aneuploid twins, because the unaffected cotwin can "mask" the abnormal serum results of an affected one. In addition, this test can designate the pregnancy as at high risk but not identify the affected fetus. Nuchal translucency (NT) screening is the best available modality and a highly effective screening method for twin pregnancies. Among twins, NT alone has a 69% DS detection rate, first-trimester combined NT and serum biochemistry has a 72% DS detection rate, and an integrated screen will have an 80% DS detection rate at a 5% FPR. The data in the literature concerning the effect of assisted conception on maternal serum screening markers in twin pregnancies are scarce. CONCLUSIONS: Down syndrome screening in assisted-conception twins presents clinical and technical challenges. Therefore, assisted-conception twins need close monitoring from conception to delivery, by a practitioner familiar with the available screening modalities and their relative accuracy.Target Audience: Obstetricians and gynecologists, family physiciansLearning Objectives: After completing this CME activity, physicians should be better able to identify the problems associated with prenatal diagnosis of Down syndrome in twins in general, and in assisted reproduction technology-conceived twins in particular, and perform the screening tests for spontaneous and assisted reproduction technology-conceived twin pregnancies, including identifying their diagnostic accuracy and pitfalls.