| Popis: |
Diagnostic tests for fetal chromosome abnormalities, principally Down's syndrome, are generally only offered on the basis of maternal age and confined to older mothers, a policy which detects only a minority (around 12%) of affected pregnancies in practice. New screening strategies based on the measurement of maternal serum markers in the second trimester in combination with maternal age have been developed. These provide an estimate of the risk (odds ratio) for individual pregnancies across the entire age range of the pregnant population. Human chorionic gonadotrophin (hCG) is the most sensitive marker and when used in conjunction with alphafetoprotein and maternal age, overall detection rates of 50–60% are possible at a false positive rate of 5–6%. Factors which may influence the final risk estimate include gestation, multiple pregnancy, threatened abortion and maternal weight. Further work is in progress to determine whether the sensitivity of biochemical screening may be improved through the use of other serum markers, notably the free β-subunit of hCG, and whether such screening can be reliably performed in the first trimester. |
