Serum human placental lactogen (HPL) levels in normal pregnancy.

It is now well established that human placenta secretes a protein hormone Human Placental Lactogen (HPL), also referred to as placental Somatomarnmotropin. It shows immunological crossreactivity with pituitary growth hormone and possesses both mammotropi.c and somatotropic effects (Jasiomovich and Maclaren, 1962, Kaplan and Grumbach 1968). This hormone is produced by syncytiotrophoblast layer of the placental epithelium (Sciarra et al, 1963). It is present in measurable amounts in early pregnancy and circulating levels in maternal serum progressively increase with advancing pregnancy' (Grumbach et al, 1958, Beck et al, 196S, Samaan et al, 1966). The introduction of the techniques of radioimrnunoassays (Yalow and Berson.