Second trimester trisomy 21 maternal serum marker screening. Results of a countrywide study of 854,902 patients

Abstract

Objectives: In France, maternal serum marker screening is governed by specific legislation. We conducted a study of the countrywide trisomy 21 screening based on second trimester maternal serum markers.

Methods: We reviewed the medical records of 854,902 patients prospectively screened for second trimester maternal serum markers in the 60 authorized laboratories over the two-year period 1997-1998. All patients screened in France were included. The risk of trisomy 21 was calculated from the combination of maternal age and maternal serum markers. The same cut-off (1/250) was used in all laboratories.

Results: In 1998, 65% of pregnant women underwent maternal serum screening. In the 837,765 patients under 38 years of age who were screened, 54,321 (6.48%; 5% CI 6.42-6.53%) had a calculated risk >1/250. Of the 884 Down syndrome cases observed, 626 were detected by maternal serum markers (70.8%; 5% CI 67.8-73.8%). These good results can be explained by a strict quality control of all steps. For the 13,891 patients over 38 years of age, the Down syndrome detection rate was 98.9% for a 34% false-positive rate.

Conclusions: Strict rules covering prenatal trisomy 21 screening are of benefit to patients, practitioners and laboratories alike, and ensure good quality control, a high trisomy 21 detection rate and a low amniocentesis rate.