Atrial natriuretic peptide levels in fetal blood in relation to inferior vena cava velocity waveforms

Objective: To determine whether blood levels of atrial natriuretic peptide in small for gestational age (SGA) fetuses are related to Doppler indices measured in arterial and venous vessels. Methods: Atrial natriuretic peptide was assayed in fetal blood obtained at funipuncture in 42 third-trimester fetuses, of whom 11 were appropriate for gestational age (AGA) and 31 were SGA. Small for gestational age fetuses were divided into three groups according to Doppler findings in the umbilical artery and inferior vena cava: 1) normal in both vessels (n = 10); 2) abnormal in the umbilical artery but normal in the inferior vena cava (n = 10); and 3) abnormal in both vessels (n = 11). Atrial natriuretic peptide levels were related to Doppler indices and acid-base status of the fetal blood. Results: Small for gestational age fetuses with abnormal waveforms in both vessels had higher atrial natriuretic peptide blood levels (median 544.8 pg/mL, range 404.2-1112.3) compared with AGA fetuses (median 316.8 pg/mL, range 159.3-470.1; P less than or equal to .001), SGA fetuses with normal waveforms only in both vessels (median 299.8 pg/mL, range 242.6-480.5; P less than or equal to .001), and SGA fetuses with abnormal waveforms only in the umbilical artery (median 367.6 pg/mL, range 192.7-748.9; P = .002). Blood levels of atrial natriuretic peptide were significantly related to the preload index in the inferior vena cava (rho = 0.554, P less than or equal to .001). This relation remained significant when the analysis was restricted to the SGA fetuses with abnormal waveforms in the umbilical artery and the inferior vena cava (rho = 0.673, P = .03). Conclusions: Small for gestational age fetuses with abnormal velocity waveforms in the inferior vena cava have significantly higher concentrations of atrial natriuretic peptide. This may represent a compensatory mechanism in the SGA fetus for regulation of an abnormal hemodynamic condition. Copyright (C) 1997 by The American College of Obstetricians and Gynecologists.