MATERNAL SERUM ALPHA-FETOPROTEIN SCREENING FOR OPEN NEURAL TUBE DEFECTS IN TWIN PREGNANCIES |
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| Authors: | H Cuckle N Wald J D Stevenson H M May M A Ferguson-Smith A Milford Ward H M Barbour K M Laurence B Norgaard-Pedersen |
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| Institution: | 1. Department of Environmental and Preventive Medicine, St Bartholomew' s Medical College, Charterhouse Square, London ECIM 6BQ, U.K.;2. Duncan Guthrie Institute of Medical Genetics, Yorkhill, Glasgow G3 SSL, U.K.;3. Supraregional Protein Reference Unit, Department of Immunology, Royal Hallamshire Hospital, Sheffield S10 2JF, U.K.;4. Department of Clinical Chemistry, Western General Hospital. Edinburgh EH4 2XU, U.K.;5. Child Health Laboratories, Department of Child Health, Heath Park, Cardiff CF4 4XN, U.K.;6. Stalen Seruminstitut, Hormone Department, Amager Boulevard 80, DK-2300 Copenhagen S, Denmark |
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| Abstract: | Data on maternal serum alpha-fetoprotein (AFP) levels at 13–24 weeks' gestation in 46 twin pregnancies with open neural tube defects (22 with anencephaly, 24 with open spina bifida) and 169 unaffected twins were used to estimate the detection and false-positive rates associated with different cut-off levels. Using the conventional cut-off level of 2·5 multiples of the median (MoM) for unaffected singleton pregnancies of the same gestation and laboratory, the detection rate in twins was 99 per cent for anencephaly and 89 per cent for open spina bifida, with a false-positive rate of 30 per cent. Using a 5·0 MoM cut-off level to maintain a similar false-positive rate to that found among singleton pregnancies at 16–18 weeks' gestation (about 3 per cent), the detection rate was 83 per cent for anencephaly and 39 per cent for open spina bifida. Estimates are provided of the odds of having an affected twin pregnancy given a positive AFP result as well as the odds for individual women with a raised AFP level. |
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| Keywords: | Alpha-fetoprotein Twin pregnancies Neural tube defects Antenatal screening Maternal serum |
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