The Influence of Maternal Weight Correction Formulas in Asian Down Syndrome Screening Using alpha-Fetoprotein and Free beta-Human Chorionic Gonadotropin

Abstract

> Objective: To investigate the relationship between maternal weight and serum alpha-fetoprotein (AFP) and free beta-human chorionic gonadotropin (beta-hCG) levels and to determine the methodology of correction formulas for influencing the results of Down syndrome screening in an Asian population. Methods: 8,194 normal singleton pregnancies without any congenital anomalies were screened using AFP and free beta-hCG between 14 and 22 weeks of gestation. Down syndrome risk was calculated by bivariate gaussian algorithm that combined information from the two biochemical measurements and maternal age. The all points regression method and median regression method were used to approach the study cases. Linear and quadratic regression correction formulas for AFP and free beta-hCG, either in analyte multiples of the median (MoM) or log analyte MoM, against maternal weight have been proposed in this study. Results: The mean maternal weight is 54.95 +/- 7.36 kg in Taiwanese pregnant women during the second trimester. There is a distinctly inverse relationship between maternal weight and serum marker levels. The log quadratic regression correction formula was the most satisfactory equation fit to the distribution of both AFP and free beta-hCG levels with a wide weight range. Routine weight correction may have the small benefit of reducing the screen-positive rate 0.36% at the risk cut-off level of 1:270. Conclusions: Maternal weight may affect the AFP and free beta-hCG levels. Although there is no discernible effect in maternal weight adjustment, it is worth making weight corrections for serum marker levels in order to reduce individual variance.