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Increases in blood volume are observed during normal gestation and these are reversed shortly after delivery. Although both atrial (A-type) natriuretic peptide (ANP) and brain (B-type) natriuretic peptide (BNP) have been described, the role of these peptides in pregnancy and the postpartum period are unclear. This study was designed to examine the effects of pregnancy, labour and delivery on plasma levels of ANP and BNP. Plasma levels of ANP and BNP were determined during normal pregnancy, 30 min after separation of the placenta (immediately postpartum) and between 5 and 72 h postpartum (late postpartum; puerperium). Since the assay sensitivity was 20 pg/ml plasma (for both ANP and BNP), values less than this were assigned a value of 20 pg/ml to calculate means. Plasma levels of ANP and BNP were significantly higher at term pregnancy than during the first trimester (ANP increased from 20 +/- 0.2 to 57 +/- 10 pg/ml (S.E.M.), P < 0.001; BNP increased from 25 +/- 2 to 49 +/- 9 pg/ml, P < 0.01). The plasma level of ANP then rose to 157 +/- 38 pg/ml 30 min after separation of the placenta, being significantly (P < 0.01) higher than that seen at term pregnancy. It declined significantly (P < 0.001) to 32 +/- 3 pg/ml in the late postpartum period. In contrast, the plasma level of BNP 30 min after separation of the placenta was 80 +/- 25 pg/ml, and increased to 116 +/- 17 pg/ml in the late postpartum period, significantly (P < 0.01) higher than the level at term pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

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