Any bag style carrier that resembles a duffel bag, with a flat bottom and two sides that slant upwards towards an elasticized or padded top, is inherently unsafe and should never be used for a newborn or small baby.
1) The bag carrier forces baby into a prone, C-shape position, tucking baby's chin to chest and potentially impeding breathing.
2) Even if a mesh panel is present, the baby's head being enclosed in fabric may cause baby to rebreathe her exhalations that are high in carbon dioxide.
3) It is difficult if not impossible for parents to view their babies' faces at all times and monitor breathing.
4) Babies may roll towards the side of the carrier and end up with their faces pressed into fabric, obstructing breathing.
Very important info to get out, since the bag style slings are VERY common and easy to find at major retailers. I wish the Maya Wrap and BabyHawk were as easy to find instead!