Reply: BMI Is a Potential Confounder of Post-Partum Relaxin-2 and Short-Term Left Ventricular Function Following Peripartum Cardiomyopathy.

In their recent publication, Damp et al. (1), reported that early postpartum levels of relaxin-2 are associated with better short-term left ventricular function in women with peripartum cardiomyopathy (PPCM). This is of potential interest given our incomplete understanding of the pathophysiology of PPCM. However, it is important to note that the investigators have not taken the women’s weight or body mass index (BMI) into account in their analyses. Relaxin-2 levels during pregnancy are inversely associated with maternal BMI from pre-pregnancy (2) and early gestation (3), whereas there are previous reports indicating that maternal BMI (non-obese vs. obese (4) and linearly (5), respectively) is inversely associated with left ventricular ejection fraction at 12 months following PPCM. Notably, the latter observations are based on the same clinical dataset as Damp et al. have based their analyses on (the IPAC [Investigations of Pregnancy-Associated Cardiomyopathy] study). As there is a large variation in the increase of relaxin-2 levels during pregnancy, it is plausible that the early post-partum levels of relaxin-2 reported by Damp et al. are correlated with the levels produced in late pregnancy. Maternal BMI could thus be an important confounder in the presented analyses on relaxin-2 and short-term left ventricular outcomes following PPCM. Preferably, maternal BMI as a potential confounder should be addressed in future investigations on the topic.