Objective: An increasing body of evidence supports a major role for the insulin-like growth factors (IGFs) in the control of human fetal growth. Individual data at various times of pregnancy suggest that IGF-I and IGF-II levels remain stable up to the 33rd week of pregnancy. Thereafter, both increase to reach values 2–3 times higher at term. In order to provide an accurate reflection of fetal IGFs in utero, we sampled fetal blood from the umbilical cord by cordocentesis. Methods: We measured IGF-I and IGF-II in 12 fetuses longitudinally for up to 5 times between the 21st week of gestation and delivery. Results: All patients showed a progressive increase in IGF-I and IGF-II levels. Data determined during different time intervals (before 29th, 29th to 32nd, after 32nd week) were compared and the main increase was found after the 32nd week. The median for IGF-I before the 29th week was 33.5 ng/ml (range 19–40.5) and increased to 41 ng/ml (32–59) between the 29th to 32nd and further to 54.1 ng/ml (range 17–70) thereafter. During the same time interval, the median for IGF-II increased from 217 ng/ml (86–326) to 349 ng/ml (227–467). In 7 patients, cord blood after delivery was available. For IGF-II a further increase was consistently found after birth (from 282 ng/ml (175–511) to 393 ng/ml (297–513)), whereas only 2 fetuses showed an increase in IGF-I. Conclusion: We conclude that in human fetuses, IGF-I and IGF-II levels increase longitudinally throughout pregnancy. Therefore, they may become important markers of healthy fetal development.

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