Placental growth hormone as a potential regulator of maternal IGF-I during human pregnancy.

Ninety-three healthy women were investigated during normal pregnancy, and 177 blood samples were obtained at various gestational stages. In 8 of the women, serial measurements were obtained over a period of 16-34 wk from 8 to 40 wk of gestation. In 13 women, daily blood samples were obtained from day 0 to day 6 after delivery. Insulin-like growth factor I (IGF-I) and human placental lactogen (hPL) were measured by radioimmunoassays. Growth hormone (GH) was estimated by two monoclonal antibody-based radioimmunoassays insensitive to physiological concentrations of hPL: the K24 assay, which recognizes only pituitary hGH, and the 5B4 assay, which reacts with all the known pituitary as well as placental GH variants. Placental GH was distinguished from the main pituitary variant through its specific immunoreactivity pattern. Mean plasma levels of IGF-I were relatively stable until 29-30 wk gestation, then increased progressively to reach a maximum at 35-36 wk. Regardless of gestational age, individual IGF-I values exhibited a highly significant positive correlation with placental GH, reflected by 5B4 immunoreactivity, whereas the correlation between IGF-I and hPL was not statistically significant. Considering each 2-wk gestational period separately, we found a positive correlation between IGF-I and 5B4 hGH at 31-32 wk. Conversely, no evidence of correlation was found between IGF-I and hPL at any period. After delivery, IGF-I evolution exhibited a biphasic pattern, with an initial decrease to low values followed by a progressive return toward levels found in nonpregnant healthy women. These results strengthen our previous hypothesis that placental growth hormone is involved in the control mechanism of serum IGF-I levels in normal pregnant women.