Embryos less than half an inch in diameter begin to attach to the wall of the uterine horns. Ideally they should be evenly spaced, as overcrowding leads to poor development and weak puppies at birth. At this stage the central nervous system is formed.
The brain and the spinal cord are developing, the embryo begins to bend it's head forward and curl up into a classic foetal position. All the organs of the body, the limbs, head, eyes and face are being formed.
The fertilized eggs have been free in the uterus and uterine tube for up to 20 days after mating, they have been surprisingly safe and immune from any infections the bitch may have suffered. Now we are entering a a very vital stage of the prospective pregnancy. If she picks up an infection, is given a live vaccine, certain medication, has an accident or becomes overheated the development of the organs of the foetus may be arrested or distorted. Deformities such as cleft palates , single eyes, under developed limbs, abnormalities of the urinary system, the heart circulatory system all occur at this time even though the foetus is only one and a half to two inches long. Foetus more badly affected may die and be reabsorbed. It is therefore important to keep the bitch away from any source of infection or gathering of dogs during this period. (Three and a half to five weeks of pregnancy) So the period before the bitch shows any clear signs of pregnancy is a very significant time in producing health puppies.
