I'm looking to analyse the serum concentration of human placental lactogen in samples obtained from maternal circulation (venous blood), as well as umbilical vein and artery. While the literature sources indicate the umbilical blood content of hPL at ranges fitting most of the commercially available ELISA kits, I have only found kits maxing out at 7000 ng/ul levels. This could be a problem as some literature cites maternal hPL levels as much higher that that maximum. Hence, does anybody have any recommendations or personal experiences with the matter and can recommend and adequate kit for maternal serum hPL level evaluation?