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Aims. The study of the morphology of coronal mass ejections (CMEs) is anauspicious approach to understanding how magnetic fields are structured withinCMEs. Although earlier studies have suggested an asymmetry in the width of CMEsin orthogonal directions, this has not been inspected using multi-viewpointobservations. Methods. We inspect the early evolution (below ten solar radii)of the morphology of a dozen CMEs occurring under specific conditions ofobserving spacecraft location and CME trajectory, favorable to reduceuncertainties typically involved in the 3D reconstruction used here. Theseevents are carefully reconstructed by means of a forward modeling tool usingsimultaneous observations of STEREO EUVI and SDO/AIA as input when originatinglow in the corona, and followed up in the outer fields of view of the STEREOand the SOHO coronagraphs. We then examine the height evolution of themorphological parameters arising from the reconstructions. Results. Themulti-viewpoint analysis of this set of CMEs revealed that their initialexpansion --below three solar radii-- is considerably asymmetric andnon-self-similar. Both angular widths, namely along the main axes of CMEs($AW_L$) and in the orthogonal direction ($AW_D$, representative of the fluxrope diameter), exhibit much steeper change rates below this height, with thegrowth rate of $AW_L$ found to be larger than that of $AW_D$, also below thatheight. Angular widths along the main axes of CMEs are on average $\approx$1.8times larger than widths in the orthogonal direction $AW_D$. The ratios of thetwo expansion speeds, namely in the directions of CMEs main axes and in theirorthogonal, are nearly constant in time after $\sim$4 solar radii, with anaverage ratio $\approx$1.6. Heights at which the width change rate is definedto stabilize are greater for $AW_L$ than for $AW_D$.

Asymmetric expansion of coronal mass ejections in the low corona