Changes in Insulin-like Growth Factor-I, Osteocalcin, and Bone Turnover in Pregnant Women

Theresa Scholl
University of Medicine and Dentistry of New Jersey
R01ES07437

Background: Preeclampsia, a complex condition involving high blood pressure, protein in the urine, and swelling, is a common and serious problem, affecting 5-10% of all pregnant women. High blood pressure during pregnancy is a very serious complication. It puts both the mother and the fetus at risk for a number of problems. Clinical trials have suggested that calcium supplementation during pregnancy reduces the incidence of preeclampsia.

Release of calcium from a pregnant woman's bones occurs during fetal development. Calcium release is a complex activity that involves bone formation and breakdown cells, growth factors, and hormones. Previous studies have shown an association between insulin-like growth factor I (IGF-I) and bone metabolism. Healthy postmenopausal women treated with IGF-I showed increased bone formation and breakdown activity as measured by biochemical markers. Osteocalcin is a protein that makes up 10-20% of the non-collagenous protein found in bone tissue. Serum osteocalcin is a marker for bone turnover. Osteocalcin is produced by bone forming cells known as osteoblasts. These investigators hypothesized that IGF-I, osteocalcin, and bone loss would be different among pregnant women with preeclampsia compared with women with normal blood pressure.

Advance: In a study of 962 healthy pregnant women, 64 went on to develop preeclampsia. In women with preeclampsia IGF-I levels were 74% greater in the 3rd trimester than the 1st while normo-tensive women experienced only a 43% increase. Osteocalcin levels in preeclamptic women were twelve times higher than normotensive during the 1st trimester. Also, women with preeclamsia had little change throughout pregnancy in their osteocalcin levels while normo-tensive women had a 63% decline in osteocalcin. Women with preeclampsia also had greater bone loss; however, this finding was not statistically significant.

Implication: This study indicates that there are different relationships between IGF-I and osteocalcin concentrations during pregnancy in women who experience preeclampsia compared with women who do not develop the condition. The findings suggest that in the 1st trimester, women who will later develop preeclampsia, there are metabolic changes associated with increasing demand for calcium mobilization as demonstrated by greater IGF-I and osteocalcin levels and loss of bone stores. The study also suggests that high levels of osteocalcin in the 1st trimester may be an early sign of the development of preeclampsia. Further studies are needed to identify the signals that are mediating the need for calcium.

Citation: Sowers M, Scholl T, Grewal J, Chen X, Jannausch M. IGF-I, osteocalcin, and bone change in pregnant normotensive and pre-eclamptic women. J Clin Endocrinol Metab. 2001 Dec;86(12):5898-903.