Impact of a two-week difference in gestational age on MoM values

This patient's gestational age at the time of blood draw was calculated to be 18 weeks based on her last menstrual period and 16 weeks based on an early ultrasound examination. The AFP, uE3, and hCG mass values calculated to a low AFP, low uE3, and elevated hCG MoM for a pregnancy at 18 gestational weeks (green circles), leading to calculation of high risk of Down syndrome. However, the same mass values for a pregnancy at 16 gestational weeks (yellow circles) were on the unaffected median (1 MoM) for each analyte, leading to calculation of low risk of Down syndrome.