We previously detected immunoreactive fibroblast growth factor 2 (FGF-2) in maternal and fetal circulations. Here, we determined whether the amounts of FGF-2 in term maternal serum, cord serum, and amniotic fluid were altered in pregnancies complicated by diabetes, as these are associated with a higher incidence of fetal macrosomia and increased placental size. Serum and amniotic fluid were collected at term from normal pregnancies (n = 17), women with pregestational insulin-dependent diabetes (n = 37; group A), patients with previously undiagnosed diabetes (n = 32; group B), women with gestational diabetes (n = 85; group C), and women with a milder form of glucose intolerance in pregnancy (n = 16; group D). Mean newborn weight and length, and placental weight did not significantly differ between normal and diabetic pregnancies, although the placental weight tended to be higher in the latter. However, 24% of the infants in group A and 19% in group B had a birth weight in excess of the 90th percentile. Levels of insulin in cord serum and amniotic fluid in groups A and B were significantly elevated compared to control values. FGF-2 was extracted from serum and amniotic fluid by heparin-Sepharose affinity chromatography and subjected to Western blot analysis or quantified by specific RIA. Western blot analysis of maternal serum, cord serum, and amniotic fluid from diabetic pregnant patients revealed, in each case, a single immunoreactive FGF-2 species of 18 kilodaltons; this was absent from nonpregnancy serum. In normal term pregnancies, the mean immunoreactive FGF-2 level in cord serum was 119 +/- 28 pmol/L, and that in amniotic fluid was 91 +/- 35 pmol/L. Values were significantly increased (2- to 4-fold) in both cord serum and amniotic fluid for all groups of diabetic patients. The mean FGF-2 level in normal term maternal serum was 104 +/- 24 pmol/L, and this was significantly increased in diabetic patients in groups B and C. The amount of FGF-2 in maternal serum showed a positive correlation with newborn weight and length, and placental weight (P < 0.05 or better, by Spearman rank correlation), and significant positive correlations also existed between the amounts of FGF-2 in cord serum and newborn or placental weight. The results suggest that the FGF-2 levels in maternal serum, cord serum, and amniotic fluid at term are elevated in pregnancies complicated by diabetes, and that the amounts of FGF-2 in maternal serum and cord serum are correlated with fetal and placental size.