Age-Based Protocol Best for Early Detection of Trisomy 18.

HOT SPRINGS, VA. - An age-based protocol for assessing maternal serum markers for trisomy 18 is much more accurate than using fixed cutoff values and would be an easy adjunct to current Down syndrome screening efforts, Dr. W. Allen Hogge said.

Better methods for early detection of trisomy 18 are needed so that affected women will know about the disorder while pregnancy termination is still an option for them. As it is now, trisomy 18 often isn't suspected until the third trimester, when severe intrauterine growth retardation is the presenting sign of the disorder for more than half of the affected fetuses, Dr. Hogge commented at the annual meeting of the South Atlantic Association of Obstetricians and Gynecologists.

In a study, Dr. Hogge and his colleagues at Magee-Womens Hospital, Pittsburgh, compared the accuracy of an age-based screening protocol that had been previously established with a system of fixed cutoff levels for maternal serum markers.

Out of a total of 45,145 patients, the fixed cutoff protocol retrospectively identified 5 of 12 cases of trisomy 18 for a detection rate of 42%. The age-based protocol identified 8 of 12, for a detection rate of 67%.

There was no significant difference seen between the false-positive rates for the fixed cutoff protocol and the risk-based approach, which were 0.25% and 0.29%, respectively.

The age-based protocol makes sense because "the risk of trisomy 18 varies dramatically based on maternal age, just as it does for Down syndrome. If you use the same cutoff value for a 20-year-old and a 34-year-old, you're likely to get ...