Pregnancy-associated plasma protein-A

Introduction

Pregnancy-associated plasma protein-A (PAPP-A) largest of the pregnancy associated proteins produced by both the embryo and the placenta (syncytiocytotrophoblasts) during pregnancy (Placenta Notes). This protein is thought to have several different functions, including preventing recognition of the fetus by the maternal immune system, matrix mineralization and angiogenesis. Levels of PAPP-A rise from first detection in the first trimester until term.

Detection of this protein is also used as a first and second trimester diagnostic test for Trisomy 21. (More? Trisomy 21 - Down Syndrome)

Maternal serum concentrations are related to subsequent fetal growth and this relationship has suggested that it can be used as a diagnostic test for adverse pregnancy outcomes (intrauterine growth restriction, premature birth, preeclampsia, and stillbirth).

Alternative names: SP4, high molecular weight alpha-2 mobile pregnancy-specific protein, IGFBP4 protease

PAPP-A Levels

Levels of PAPP-A rise from initial detection at about 32 days after ovulation, then increasing rapidly (levels doubling every 3 days), finally continuing to rise more slowly until term.

Electroimmunoassays allow the detection as early as the fifth week of pregnancy, of circulating levels down to 10 microgram/L.

Adult male serum PAPP-A circulating level is 8.03±2.75 mIU/L (mean±SD).