The influence of maternal weight on human chorionic gonadotropin in the multiple-marker screening test for fetal Down syndrome.

OBJECTIVE: Our purpose was to determine the effect of maternal weight on human chorionic gonadotropin concentration in the multiple-marker screening test for fetal Down syndrome. STUDY
DESIGN: Two genetics databases were used: database I contained the results of 8297 multiple-marker screening tests and database II contained the results of 1936 multiple-marker screening tests and fetal karyotypes.
RESULTS: The overall screen-positive rate in database I was 7.1%; it was 7.5% in patients weighing < 180 pounds and 5.1% in patients weighing > or = 180 pounds (p = 0.001). Weight significantly affected the screen-positive rate only in women > or = 30 years old (p = 0.003 for 30 to 34 years, p = 0.00004 for > or = 35 years). A weight correction formula was derived; when applied to database II it eliminated individual weight-related differences but had no effect on the overall screen-positive rate or Down syndrome detection rate.
CONCLUSIONS: Human chorionic gonadotropin concentration is affected by maternal weight. A weight correction formula eliminates individual weight-related differences in the screen-positive rate but has no discernible effect on the overall screen-positive or Down syndrome detection rates.