Maternal body weight and first trimester screening for chromosomal anomalies

Abstract

Prenatal risk ratios for Down syndrome adjust for maternal weight because maternal serum biomarker levels decrease with increasing maternal weight. This is accomplished by converting serum biomarker values into a multiple of the expected median (MOM) for women of the same gestational age. Weight is frequently not recorded and the impact of using MOMs not adjusted for weight for calculating risk ratios is unknown. The aim of this study is to examine the effect of missing weight on first trimester Down syndrome risk ratios by comparing risk ratios calculated using weight-unadjusted-and -adjusted MOMs. Findings at the population level indicate that the impact of not correcting for maternal weight on first trimester screening results for chromosomal anomalies would lead to 84 per 10,000 pregnancies changing from negative to positive and 56 per 10,000 pregnancies changing from positive to negative. PAPP-A. Antenatal and birth data for the study region was recorded in an electronic obstetric surveillance system. Information from the obstetric database used in this study included: selfreported pre-pregnancy weight and height, parity, smoking status during pregnancy, chorionic villus sampling < 20 weeks, amniocentesis <20 weeks, any birth defect and birth outcome. Body mass index (BMI; kg/m 2 ) was calculated using maternal weight and height from the obstetric database and categorised using international standards.

Behavior of the Genetic Markers at Screening during the First Trimester of Pregnancy in Euploid Fetuses

“…A similar result for PAPP-A was obtained in Australia, where it was found an inverse relation between maternal BMI and the values of free β-HCG and PAPP-A. 33 Spencer et al 18 also found a direct relation between PAPP-A and gestational age. Moreover, the presence of trisomy 21 has been associated with lower levels of PAPP-A and higher levels of free β-HCG.…”