N-Terminal pro-B-Type Natriuretic Peptide Concentrations in Mothers just before Delivery, in Cord Blood, and in Newborns

The role of the heart as an endocrine organ was established in 1981 by de Bold et al. (1). Usually, in adults, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted mainly by the cardiac atria and ventricles, respectively (2). Plasma concentrations of these peptides, particularly that of BNP, have been shown to reflect cardiac dysfunction and volume overload in adults and children (3)(4)(5)(6)(7)(8). There is evidence that these peptides have possible roles during fetal life in the regulation of organogenesis of the heart and the cardiovascular system, in the regulation of blood pressure and water balance in the developing embryo, and in the transition from fetal to extra-uterine life (9). BNP may also have an important role in the regulation of amniotic fluid volume (10). Sparse data exist regarding N-terminal proBNP (NT-proBNP) concentrations in umbilical cord blood and in the newborn during the first days of life (4)(11)(12)(13). In most of these studies, plasma concentrations of the peptide showed marked increases in the first day of life with a steady decrease during the first 5–7 days (4)(11)(12)(13). Because NT-proBNP may be used as a marker for various pathologic conditions in perinatal medicine, we conducted a study to determine reference values for NT-proBNP in cord blood and in newborn blood compared with maternal blood. EDTA-plasma NT-proBNP was measured in blood collected from 71 mothers just before delivery, from 122 umbilical cords, and from 33 full-term healthy newborns in the first days of life. Of 122 newborns enrolled in the study, 110 were delivered vaginally and 12 by cesarean section. NT-proBNP was measured with an electrochemiluminescence immunoassay (Elecsys 1010/2010; Roche). The assay is unaffected by icterus (bilirubin <350 mg/L), hemolysis, or lipidemia. The mean (SD) NT-proBNP concentration in maternal blood (n = 71) was 88.5 (44.9) ng/L, the mean concentration in cord blood (n = 122) was 578.8 (351.3) ng/L, and the mean plasma NT-proBNP concentration in the newborns (n = 33) was 3042.4 (1783.2) ng/L. For paired samples, there was a significant difference between maternal predelivery NT-proBNP concentrations and umbilical cord NT-proBNP concentrations [89.7 (45.4) vs 612.2 (364.5) ng/L, respectively; P <0.0001; n = 66]. We found no correlation between cord blood NT-proBNP concentrations and newborn weight loss. There were no differences in NT-proBNP concentrations in cord blood and in newborns related to gender, gestational age, mode of delivery, duration of labor, or Apgar scores. Because the reference values for the natriuretic peptides, including NT-proBNP, are assay specific (11)(14)(15), the use of different assays in the published studies makes it difficult to draw conclusions and relate to the currently published baseline values (11)(12)(13). Our report includes NT-proBNP concentrations for 71 mothers just before delivery, 122 umbilical cord blood samples, and 33 full-term newborns (ages, 1–4 days) measured by the Roche proBNP assay. In agreement with previous studies (11)(12)(13)(16), our study shows low NT-proBNP concentrations in prelabor maternal blood, intermediate concentrations in cord blood, and high concentrations in newborn blood in the first 4 days of life. Using the same assay, Bakker et al. (13) reported a mean umbilical cord NT-proBNP concentration of ∼80 pmol/L (670 ng/L), which is comparable to our result of 600 ng/L (1 pmol/L = 8.47 ng/L). Although this study was carried out on a relatively small population of newborns, the results of our study may be used as an additional reference baseline for comparing NT-proBNP concentrations in cord blood and plasma of neonates with heart disease, pulmonary problems, or with water and electrolyte disorders in which volume overload and cardiac dysfunction are involved. The results should be compared with regard to the assay used.