Legg–Calvé–Perthes syndrome, which causes the top of the femur (thigh bone) to degenerate, occurs in Yorkies in certain lines. The condition appears to result from insufficient circulation to the area around the hip joint. Usually a teacup is any dog weighing less than 4 lb (1.8 kg) when fully grown, when the actual breed standard is given at 7 lb (3.2 kg) maximum. Breeding for 'teacup' size is a controversial practice that is not encouraged by responsible breeders.They are bred to appeal with their puppy-like features, rather than bred to avoid health issues. There is great risk to a dam (mother) during pregnancy who is too small; most of these litters are born as a result of Caesarean sections and have a high mortality rate.There are many health issues associated with teacup dogs, such as luxating patellae, heart disease, hydrocephalus, hypoglycaemia, chronic pelvic pain syndrome, open fontanels and seizures.