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Background: Abnormal fetal growth can lead to adverse outcomes in pregnancy as well in later postnatal life and is more prevalent in diabetic pregnancies. These are usually associated with large for gestational age neonates, an issue that has already been broadly examined. On the other side, diabetes in pregnancy can also relate to intrauterine growth restriction and small for gestational age neonates. During pregnancy, maternal IGF-1 is secreted excessively and additionally produced by placenta, which regulates transport of nutrients to the fetus acting through an IGF-receptor and accordingly affects its growth. As type 1 diabetes carries a higher risk of adverse events associated with fetal growth there is a natural focus on possible links between IGF-1 and fetal growth.

Aim: The present study investigated the time-course relationship between the maternal serum IGF-1 and the birthweight as an obstetrical outcome in type 1 diabetic pregnancies with various levels of background risk.

Methods: 130 pregnant women with type 1 diabetes were consecutively recruited for measurement of growth factors, genes affecting coagulation, evaluated for diabetes status, and perinatal outcome. The birthweight z-score was computed and grouped into tertiles for analysis of association with repeated measurements of IGF-1. Diurnal blood pressure was measured by monitor. Retinopathy grade was evaluated by two specialists independently, blinded of the clinical data. Blood samples for IGF-1 during pregnancy were drawn from week 6 and every 4th week until week 30, then every 2 nd week. Genomic DNA was extracted from peripheral blood.

Results: The median of the lowest tertile of birthweight z-score was 0.4 (-1 - +1.3) and included more women with micro/macroalbuminuria than the middle and upper tertile; however, ¾ had normoalbuminuria and no further sign of surplus vasculopathy compared to the other tertile groups. The lowest birthweights were associated with a lower rise in IGF-1 from week 22 to 32. Neither glycemic control, genetics, grade of retinopathy, renal function nor vascular resistance indices in diurnal blood pressure were different between the tertile groups.

Conclusion: Our main finding is that lower IGF-1 levels are associated with subsequent lower birthweight in diabetic pregnancy and is displayed markedly at the end of 2nd trimester. We hypothesize that the relative low birthweight, despite being within the limits of appropriate for gestational age may display inappropriate growth if not outright growth-restriction. We were able to discern different levels of growth at a critical point in pregnancy where ultrasound may pick up different levels of growth patterns and optimized care can be commenced.