The ratio between molecular variants of pregnancy-specific beta 1 glycoprotein (SP1) in the peripheral and retroplacental circulation during later pregnancy.

The ratio between two molecular variants of pregnancy-specific beta 1 glycoprotein (SP1) in the peripheral and retroplacental circulation was analysed in nine women during late pregnancy. The ratio between the two molecular variants, i.e. SP1 beta and SP1 alpha, was found to be identical in the peripheral and retroplacental circulation in all women examined. Comparisons were also made between SP1 beta as measured by radioimmunoassay and a normal serum protein, alpha 2 macroglobulin. A positive concentration gradient from peripheral to retroplacental circulation was found for SP1 beta whereas the gradient was less pronounced for alpha 2 macroglobulin. These findings add weight to the concept that SP1 alpha is a unique molecular species and not a genetic variant or a product of SP1 beta.