Increase in maternal placental growth hormone during pregnancy and disappearance during parturition in normal and growth hormone-deficient pregnancies

OBJECTIVE: The purpose of this study was to evaluate placental growth hormone levels in maternal circulation throughout pregnancy in normal and growth hormone-deficient women with the use of a specific assay and to determine the clearance of placental growth hormone from maternal circulation after birth. STUDY DESIGN: Seventeen healthy pregnant women and 1 patient with growth hormone deficiency substituted with recombinant growth hormone during pregnancy participated in a longitudinal study from early pregnancy until birth with repetitive blood sampling and measurement of placental growth hormone levels throughout pregnancy Furthermore, serial blood samples were drawn before, during, and after elective caesarean deliveries in 5 healthy women to calculate the half-life of placental growth hormone. Placental growth hormone was measured with the use of two monoclonal antibodies in-a commercially available solid-phase iodine 125-labeled immunoradiometric assay (Biocode, Liege, Belgium). RESULTS: Placental growth hormone levels were detectable from as early as 8 weeks of gestation in some of the women and increased throughout gestation, with a maximum at approximately 35 to 36 weeks of gestation (13.7 ng/mL; range, 5.9-24.4 ng/mL) and large interindividual variations. Placental growth hormone levels did not correlate with birth weight or placental weight. In the patient with isolated growth hormone deficiency, placental growth hormone levels were detectable from 11 weeks of gestation (3.4 ng/mL) and increased throughout pregnancy to 13.9 ng/mL, which is similar to values that are obtained in the healthy pregnant women. Substitution therapy with recombinant human growth hormone did not suppress the increase in placental growth hormone. We found a mean half-life of placental growth hormone of 13:8 minutes (range, 11.5-15.2 minutes) in healthy pregnant women and an apparently similar half-life of placental growth hormone (15.8 minutes) in the growth hormone-deficient patient, assuming a monoexponential disappearance of placental growth hormone during the first 30 minutes after the delivery. After the initial 30 minutes, approximately 75% (range, 65%-89%) of the placental growth hormone had been cleared from the maternal circulation. CONCLUSION: Levels of placental growth hormone in maternal circulation increase throughout pregnancy from as early as 8 weeks of pregnancy, with maximum levels around the week 35 of gestation. The pregnancy-induced rise in placental growth hormone levels in the growth hormone-deficient patient was comparable to the rise seen during normal pregnancies and was not suppressed by the concurrent human growth hormone treatment. We speculate that maternal serum levels of placental growth hormone reflect placental function and fetal growth. However, further studies are needed to evaluate the potential clinical use of placental growth hormone determinations.