Selective use of maternal serum testing.
Maternal serum testing is used to screen for both trisomy 21 (T21) and structural fetal abnormalities such as neural tube defects (NTDs). Second line diagnostic testing for T21 is usually by amniocentesis but for NTDs it is simply a detailed scan. It is possible that a proportion of women unnecessarily reject both parts of the screening test because they would not wish to undergo invasive testing and yet would accept a detailed ultrasound scan. This is particularly important in maternity units, such as ours, which cannot yet offer detailed fetal anomaly scans routinely. A retrospective case-note review of 231 consecutive new bookings over a 4-month period identified 61 women who chose initially not to have serum measurement of AFP/hCG (double test). Of the 61 women, 23 had rejected serum testing because they would not agree to amniocentesis and 29 because they would not agree to termination of pregnancy. All 61 women were offered serum screening for structural anomalies alone and 21 (34%) then chose to have AFP measurement. Maternal serum screening is not a single test and clinicians working in units with a limited antenatal ultrasound service should consider offering AFP measurement alone to women who decline comprehensive testing.
Montague
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Directorate of Obstetrics, Gynaecology and Paediatrics, Taunton and Somerset Hospital, UK.
Fox
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R