Objective: To measure plasma atrial natriuretic peptide (ANP) in relation to maternal haemodynamics and body fluid balance in the early puerperium following uncomplicated pregnancy and pre-eclampsia.
Design: A longitudinal study from late pregnancy and into the early postpartum period (days 1 to 3 and days 4 to 6) compared with nonpregnant controls.
Subjects: Eleven women with uncomplicated pregnancies, 12 women with pre-eclampsia and 12 healthy, nonpregnant women.
Main outcome measures: Maternal heart dimensions determined by M-mode echocardiography, concentrations of ANP, and daily urine output and sodium excretion.
Results: After delivery increases in left atrial dimensions, represented as mean (SEM), from 33.2 (1.6) to 37.7 (1.7) mm and ANP levels from 7.9 (1.1) to 19.0 (2.7) pmol/L were observed at 1-3 days postpartum in normal pregnant women, but we were not able to demonstrate a significant increase in diuresis and natriuresis. In the third trimester left atrial dimensions (38.4 (1.2) mm) and ANP levels (15.4 (2.2) pmol/L) were greater in pre-eclampsia. ANP levels rose further in pre-eclamptic women in the early puerperium (27.4 (7.4) pmol/L) with an increase in diuresis and natriuresis, while left atrial dimensions did not change significantly (39.4 (1.7) mm). A pericardial effusion was found in 11 pre-eclamptic but in only three healthy pregnant women.
Conclusions: A concommitant increase in left atrial dimensions and ANP in the early puerperium following uncomplicated pregnancies is consistent with the mechanism of atrial stretch as a stimulus for ANP release, although the biological significance of this finding remained unclear. A significantly higher release of ANP in the early puerperium after pregnancies complicated by pre-eclampsia may be a mechanism which promotes the renal elimination of excessive body fluids and sodium.