Maternal and fetal atrial natriuretic peptide levels at delivery from normal and growth retarded pregnancies.

OBJECTIVE: To determine whether circulating fetal levels of the vasodilator atrial natriuretic peptide (ANP) are reduced in pregnancies complicated by intrauterine growth retardation (IUGR). DESIGN: Prospective observational study. SETTING: University teaching hospital and research laboratory. SUBJECTS: 25 normal singleton pregnancies delivered at term by spontaneous vertex delivery (n = 16) or by elective caesarean section (n = 9), and a series of 14 singleton pregnancies complicated by IUGR. INTERVENTION: Measurement of ANP by radio-immunoassay in maternal venous, umbilical artery, and umbilical vein plasma from a series of normal, and IUGR pregnancies. MAIN OUTCOME MEASURES: Comparison of plasma ANP levels between the three groups; relation between fetal ANP, PO2 and pH. RESULTS: Mode of delivery did not influence either maternal, umbilical artery or umbilical vein plasma ANP levels in normal term singleton pregnancies. Umbilical vein ANP levels were significantly higher in the IUGR group when compared with normal pregnancies at term (mean 66 95%, CI 36-122 vs mean 37, 95% CI 29-47 pg/ml, P = 0.03) and were inversely related to umbilical artery pH (R2 = 65%; P = 0.003). CONCLUSIONS: These data suggest that umbilical vein ANP levels are elevated in pregnancies complicated by IUGR, and rise appropriately in response to the stress of acidosis. In the absence of any receptor or second messenger defect within feto-placental vascular smooth muscle, these data suggest that ANP is not directly implicated in the vascular pathophysiology of IUGR.