Constraints in the ω_b-N_eff plane from the CMB and abundance measurements. The blue stripes shows the 68% confidence regions from measurements of primordial element abundances assuming standard BBN: ⁴He bounds compiled by Aver et al. (2012); and deuterium bounds complied by Iocco et al. (2009) or measured by Pettini & Cooke (2012). We show for comparison the 68% and 95% contours inferred from Planck+WP+highL, when N_eff is left as a free parameter in the CMB analysis (and Y_P is fixed as a function of ω_b and N_eff according to BBN predictions). These constraints assume no significant lepton asymmetry.