BNP in Pregnancy
BNP in Pregnancy
Abstract & Commentary
By Michael H. Crawford, MD
Source: Tanous D, et al. B-Type natriuretic peptide in pregnant women with heart disease. J Am Coll Cardiol. 2010;56:1247-1253.
Increases in cardiac volume in the non-pregnant state increase BNP, but little is known about pregnancy and BNP levels. Thus, these investigators from London and Toronto, Ontario, Canada, sought to elucidate changes in BNP during pregnancy in normal women and those with heart disease, and determine the relationship between BNP levels and cardiac events during pregnancy. A total of 66 pregnant women with heart disease were prospectively enrolled and compared to 12 controls without heart disease. Of the 66 women with heart disease, 49 had congenital heart disease, but none were cyanotic. BNP levels were measured in the first trimester, the third, and after delivery. BNP levels were low and did not increase during pregnancy in the normal women. In women with heart disease, BNP levels were higher than the controls (peak median 79 pg/mL vs. 35 pg/mL, p < 0.001). In those with heart disease, peak median BNP ranged from 15 to 1,425 pg/mL, and was highest in those with left ventricular dysfunction (137 pg/mL). During pregnancy, BNP levels > 100 pg/mL were observed in 38% of the women with heart disease; 5% had values > 500 pg/mL. No normal control had values > 100 at any time during pregnancy. All women who exper- ienced cardiac events during pregnancy had a BNP > 100, and none of those with BNP < 100 had an event (negative predictive value = 100%). The authors concluded that in women with heart disease, BNP levels are often elevated and may help determine if adverse events are cardiac in origin.
Commentary
Cardiologists are frequently consulted when women with heart disease become pregnant and there is considerable anxiety about their risk for adverse cardiac events. This study suggests that a normal BNP level is strong reassurance that the woman is handling the hemodynamic load of pregnancy and adverse cardiac events are unlikely. An elevated BNP would increase the risk of an event, but the positive predictive value is difficult to determine from this study since some BNP values were drawn after an event occurred. Also, many patients with elevated BNP had no evidence of heart failure and never had events. BNP values were highest in those with known left ventricular dysfunction, and previous studies have shown that NYHA class and an abnormal left ventricular ejection fraction predict adverse cardiac events in pregnant women with heart disease. Although BNP is elevated in preeclampsia, it does not predict fetal events or pregnancy associated hypertension. Thus, like other clinical applications of BNP measurements, they are most useful when normal.
The major limitation of this study is the small number of subjects. This made the evaluation of the value of BNP in subgroups by cardiac diagnosis impossible. Also, BNP was measured in the first and third trimesters, and most had an increase between these two measurements. Often, high values were noted only after an event. The value of second-trimester measurements is unknown, but may increase the value of BNP measurements. In addition, women with structurally normal hearts and arrhythmias were not studied, yet this is a common problem in pregnancy. Finally, these women were cared for in specialized centers that may achieve better outcomes than obstetric units in general hospitals.
How should we apply this new information? It does not seem warranted to measure BNP levels in all pregnant women to screen for heart disease. In women with known heart disease, an initial BNP when pregnancy is diagnosed seems reasonable, but if it is normal, should you do a second one, and when? Certainly, if an event occurs that may be cardiac, a BNP level would be of value. If everything is going well, it may make sense to do another level in the late second or early third trimester to be sure there is no subclinical deterioration in hemodynamic status after the full effect of blood volume and cardiac output increases have been experienced for awhile.
Increases in cardiac volume in the non-pregnant state increase BNP, but little is known about pregnancy and BNP levels.Subscribe Now for Access
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