Qualitative detection of a human placental lactogen--binding substance by radioassay.

Serum levels of human placental lactogen (hPL) were measured by radioimmunoassay, and a method was developed for the detection of an hPL-binding substance by radioassay. Three groups of women were investigated: (1) normal adult women who had never been pregnant; (2) women with normal pregnancies; (3) high-risk pregnant women (those demonstrating low levels of hPL). All women who had never been pregnant and most women who had normal hPL levels were found to be negative for the hPL-binding substance, whereas 80% of the women with hPL levels less than 4.0 nanograms per mililiter in the third trimester were positive for the hPL-binding substance. The presence of an hPL-binding substance might have a significant effect on pregnancy, since it could bind and reduce the functional availablity of hPL or disrupt normal production of it, thus causing fetal loss or premature delivery.