Normal amino-terminal pro-brain natriuretic peptide (NT-proBNP) values in amniotic fluid.
BACKGROUND
Brain natriuretic peptide (BNP) is synthesized by human fetal membranes, both the amnion and chorion. This locally produced BNP inhibits the contraction of the human myometrium, contributing to the maintenance of myometrial quiescence during pregnancy. Reference values for NT-proBNP concentrations in amniotic fluid at different gestational ages have not been completely defined. We aimed to investigate the range of fetal NT-proBNP values in amniotic fluid in normal pregnancy between 17 and 41weeks of gestation.


METHODS
Samples of amniotic fluid were obtained from women meeting the following inclusion criteria: gestational age defined by early ultrasound, singleton gestation and not in labor. The exclusion criteria were as follows: multiple gestation, clinically evident chorioamnionitis, laboratory signs of infection in the amniotic fluid sample and fetal conditions that may alter NT Pro-BNP levels (anemia, hydrops, etc.). NT-proBNP concentrations in amniotic fluid were measured using the automated Elecsys® proBNP assay.


RESULTS
We analyzed 218 samples of amniotic fluid at various gestational ages. Half of the samples were obtained by amniocentesis (118 samples), and the other half (100 samples) were obtained by direct puncture at the time of cesarean section. We found a significant decline in NT-proBNP concentrations with advancing gestational age.


CONCLUSIONS
Gestational age has to be taken into consideration in the assessment of NT-proBNP values. Our data may be used as reference values in fetal medicine, as a possible predictor of preterm delivery risk using the inferior limit (0.5 multiples of the median (MoM)) of our normal curve.
Unidad de Medicina Materno Fetal, División de Obstetricia y Ginecología, Escuela de Medicina, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile. Electronic address: jcarva@med.puc.cl.
Jorge Andrés
JA
Carvajal
Unidad de Medicina Materno Fetal, División de Obstetricia y Ginecología, Escuela de Medicina, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile. Electronic address: fferrer@med.puc.cl.
Fernando Andrés
FA
Ferrer
Unidad de Medicina Materno Fetal, División de Obstetricia y Ginecología, Escuela de Medicina, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile. Electronic address: fsaraya@uc.cl.
Francisca Isabel
FI
Araya
Unidad de Medicina Materno Fetal, División de Obstetricia y Ginecología, Escuela de Medicina, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile. Electronic address: delpiano@med.puc.cl.
Ana María
AM
Delpiano
D000653:Amniotic Fluid / Q000378:metabolism*; D005260:Female; D006801:Humans; D020097:Natriuretic Peptide, Brain / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011247:Pregnancy; D012016:Reference Values
D010446:Peptide Fragments; C109794:pro-brain natriuretic peptide (1-76); D020097:Natriuretic Peptide, Brain
Amniotic fluid; Fetal membranes; N-terminal pro-B-type natriuretic peptide; Reference value