The welfare of eggs during transport from breeder farms to hatcheries, and during incubation, raises emerging ethical questions as evidence accumulates about avian embryo sentience during late incubation. Fertilised eggs are transported over distances of hundreds of kilometres in temperature-controlled vehicles; transport quality affects hatchability and chick quality. Suboptimal temperature, vibration, and humidity during transport cause embryo mortality and developmental abnormalities. Evidence suggests avian embryos develop pain-relevant neural structures and begin responding to noxious stimuli from around day 13 of a 21-day incubation period. Welfare science is beginning to consider embryo welfare in relation to hatchery practices including over-sexing, culling of male chicks at hatch, and suboptimal incubation conditions. In-ovo sexing technology - determining chick sex within the egg before hatching - offers welfare-positive alternatives to day-old male chick killing. Several European countries have mandated in-ovo sexing adoption.