Prospective Observational Study of N-terminal Pro-Brain Natriuretic Peptide Levels in Obese and Nonobese Women during Pregnancy.

OBJECTIVE

N-terminal pro-brain natriuretic peptide (NT-proBNP), a marker of ventricular dysfunction, varies by body mass index (BMI) outside of pregnancy. This study aimed to determine whether obesity affects NT-proBNP levels in pregnancy.

STUDY DESIGN

This was a prospective observational study of healthy pregnant people in the third trimester (3TM) and postpartum (PP). Patients were excluded if they had significant medical comorbidities or if their fetuses had anomalies, growth restriction or aneuploidy. NT-proBNP was measured at 28 weeks (3TM), predelivery (PD), 1 to 2 days PP (immediate postpartum [IPP]), and 4 to 6 weeks PP (delayed postpartum [DPP]). LogNT-proBNP levels were analyzed using linear mixed effects models, including BMI < or ≥30, time, and time-by-BMI interactions.

RESULTS

Fifty-five people (28 [51%] with BMI ≥ 30 and 27 [49%] with BMI < 30) were enrolled. A greater proportion of obese than nonobese subjects developed hypertensive disorders of pregnancy (50 vs. 15%,  = 0.010) and obese patients had higher systolic blood pressures at all time points ( < 0.05). NT-proBNP levels (median [interquartile range] in pg/mL) were 18 (6-28) versus 26 (17-48) at 3TM, 16 (3-38) versus 43 (21-60) at PD, 58 (20-102) versus 63 (38-155) at IPP, and 33 (27-56) versus 23 (8-42) at DPP for obese compared with nonobese patients. In linear mixed effects models, logNT-proBNP was lower in obese patients at 3TM (β = -0.89 [95% confidence interval, CI: -1.51, -0.26]) and PD (β = -1.05 [95% CI: -1.72, -0.38]). The logNT-proBNP trends over time differed by BMI category, with higher values in obese patients at both PP time points compared with the 3TM (IPP β = 1.24 [95% CI: 0.75, 1.73]; DPP β = 1.08 [95% CI: 0.52, 1.63]), but only IPP for nonobese patients (β = 0.87 [95% CI: 0.36, 1.38]).

CONCLUSION

Obese patients had lower NT-proBNP levels than nonobese patients during pregnancy but not PP. The prolonged PP elevation in NT-proBNP in obese patients suggests that their PP cardiac recovery may be more prolonged.

KEY POINTS

· NT-proBNP levels are lower in obese than nonobese patients during pregnancy.. · Levels remain elevated in obese, but not nonobese, patients up to 4 to 6 weeks' postpartum.. · A lower threshold for concern regarding NT-proBNP levels may be needed in obese pregnant people..