Background: Insulin-like growth factors (IGFs) are anabolic proteins
that are essential regulators of cell division, differentiation and growth. We
describe the longitudinal changes in IGF-I, IGF-II and the binding proteins IGFBP-1,
-2 and -3 before and during normal pregnancy.
Method: Serum samples were taken before conception and then at 12, 24
and 36 weeks of gestation in 41 healthy women with uncomplicated pregnancies. We
measured IGF-I using an automated chemiluminescent method, IGF-II and IGFBP-2 using
in-house radioimmunoassays (RIAs), and IGFBP-1 and IGFBP-3 using commercial
enzyme-linked immunosorbent assay (ELISA) and RIA kits, respectively. Because of the
potential haemodilution effects during pregnancy, albumin was also measured in all
samples.
Results: There was a significant fall in IGF-I during the first (36%)
and second trimesters (21%) followed by an increase of 25% at 36 weeks. During
pregnancy, the mean IGF-II concentrations fell by 12% at 12 weeks, 8% at 24 and 8% at
36 weeks compared with pre-conception values. When IGF-II results were adjusted for
the haemodilution of pregnancy, its concentrations increased. During pregnancy, there
was a rapid increase in mean IGFBP-1 levels by 17-fold (12 weeks), 24-fold (24 weeks)
and 25-fold (36 weeks). IGFBP-2 concentrations fell after conception but started to
increase towards term. This increase was more significant when adjusted for
haemodilution. In contrast, IGFBP-3 concentrations increased significantly throughout
pregnancy.
Conclusion: Our data on the physiological changes of IGFs and their
binding proteins add further evidence of the vital roles of these hormones throughout
normal pregnancy.
