Spontaneous fluctuations of human placental lactogen during normal pregnancy.

Six women in the 3rd trimester of normal pregnancy had measurements of circulating placental lactogen (hPL) levels using a continuous blood sampling technique for 10-15 h. In addition, in 3 pregnant women hPL was assayed at 10-min intervals for 60-90 min. Both these procedures showed that hPL serum levels fluctuate irregularly during normal pregnancy. The magnitude and frequency of these fluctuations make the significance of a single hPL determination less reliable as a test of placental function.