LEP and atrial fibrillation: However, taking into account that leptin was detectable in maternal serum at all the gestational days studied, displaying similar levels throughout the studied days, unlike what was found in the AF, it is reasonable to suggest that the sudden appearance of leptin in the AF at day 20 must be primarily related with another specific source, and the placenta might be one of the most relevant candidates, since this is an important source of leptin during gestation [10,50].