Nutrition plays an important role in regulating the circulating levels of
insulin-like growth factor-I (
IGF-I). We have demonstrated that reduced
nitrogen balance is related to changes in serum
IGF-I levels but not serum
growth hormone levels in pregnant rats. In the present study, we investigated the effects of changes in
nitrogen balance on serum
IGF-I levels in normal and malnourished pregnant women (defined as having negative
nitrogen balance). Forty-eight pregnant women (
threatened miscarriage and
premature labor, 39;
pre-eclampsia, 3; hyperemesis, 3;
ileus, 2;
bleeding from the colon, 1) and 19 non-pregnant women admitted in Kobe University Hospital were enrolled in this study. Blood samples of normal pregnant controls were also obtained from 172 healthy pregnant women attending the outpatient clinic. Serum
IGF-I levels and
nitrogen balance were measured serially in 9 pregnant women with
threatened miscarriage and
premature labor and 9 malnourished pregnant women out of 48 pregnant women. Serum
IGF-I and urinary
nitrogen levels were measured by radioimmunoassay with
acid-
ethanol extraction and the Dumas method, respectively.
Nitrogen balance was expressed as the difference between daily
nitrogen intake and
nitrogen excretion assessed by urinary
nitrogen levels. Serum
IGF-I levels in normal pregnant controls significantly increased in the third trimester of pregnancy compared with non-pregnant controls. No difference in serum
IGF-I levels in any trimester of pregnancy was observed between normal pregnant controls and pregnant women with
threatened miscarriage and
premature labor. There was no significant difference in
nitrogen balance between the pregnant women with
threatened miscarriage and
premature labor and non-pregnant controls. In the longitudinal study, no correlation was found between the changes in serum
IGF-I levels and those in
nitrogen balance in the 9 pregnant women with threatened
premature labor (daily
nitrogen balance > 0 g/day) on the basis of linear regression analysis. On the other hand, the changes in serum
IGF-I levels in the 9 malnourished pregnant women were significantly correlated with those in
nitrogen balance (y = 1.72x + 17.5; r = 0.60; P < 0.05: linear regression analysis). These results indicate that maternal nutritional states have a major effect on serum
IGF-I levels in malnourished pregnant women, but not in pregnant women with daily
nitrogen balance > 0 g/day. Serum
IGF-I levels can be a potent index of nutritional states under
malnutrition during human pregnancy.