Effect of gestational age on first trimester maternal serum prenatal screening correction factors for ethnicity and IVF conception

Objective The aim of this study is to investigate gestational age effects of maternal ethnicity and in vitro fertilization (IVF) pregnancy correction factors of first trimester trisomy 21 screening markers pregnancy associated plasma protein A (PAPP-A) and free-β human chorionic gonadotropin (free hCGβ) in a large dataset. Methods Data from 205 341 normal singleton pregnancies were retrieved, and PAPP-A and free hCGβ concentrations were converted to multiples of the medians (MoMs) uncorrected for either maternal ethnicity or IVF pregnancy. Log10 transformed MoMs were plotted against gestational age in each group to examine gestational age effects Results Significant gestational age effects were found for correction factors for PAPP-A in Afro-Caribbean, South Asian and East Asian, and for free hCGβ in Afro-Caribbean and IVF pregnancy. Conclusions Current single correction factors for PAPP-A and free hCGβ based on maternal ethnicity and IVF pregnancy are inappropriate, and future screening algorithms need to take into account the change in effect of these factors with gestational age. © 2012 John Wiley & Sons, Ltd.