Objective: To examine whether adrenomedullin, a novel vasoactive peptide produced by the placenta, participates in the uteroplacental hemodynamic alterations in intrauterine growth restriction, we studied the correlation between adrenomedullin levels and fetoplacental blood flow. Study Design: Maternal and umbilical blood samples were collected in pregnancies complicated by intrauterine growth restriction with abnormal umbilical artery Doppler findings and in control pregnancies. Adrenomedullin levels were measured by means of a specific radioimmunoassay, and flow velocimetry waveforms were recorded from uterine, umbilical, and fetal middle cerebral arteries. Results: Mean adrenomedullin values in umbilical plasma were higher (P <.05) in patients with intrauterine growth restriction (63.7 ± 34.2 pg/mL; n = 16) than in control subjects (38.1 ± 14.8 pg/mL; n = 16). A significant correlation was found between maternal adrenomedullin levels and umbilical artery pulsatility index. Moreover, fetal adrenomedullin concentrations correlated negatively with middle cerebral artery pulsatility index and positively with umbilical artery pulsatility index/middle cerebral artery pulsatility index ratio. Conclusion: This study provides evidence that adrenomedullin is increased in fetuses with intrauterine growth restriction in response to reduced uteroplacental blood flow and suggests that it may participate in the fetal hemodynamic modifications. (Am J Obstet Gynecol 2000;182:650-4.)