I think this is what you are referring to.
The first week of pregnancy
Fertilization occurs and the embryos are in the oviduct.
During the second week
The embryo will grow from a 4 cells to 64 cells and it will enter the uterus.
The embryos implant in the uterus.
The embryo develop eyes and spinal cords and their faces take shape. They are most susceptible to defects at this stage. It may be possible to feel for puppies at this point.
Puppies develop toes, claws and look like dogs now. Their gender can be determined and their eyes are closed. They are now pretty resistant to developmental problems at this stage.
During this week the pups develop skin pigment. they weigh around 6 grams. Fetal heartbeats can be heard with stethoscope by a trained individual.
Pups continue to grow and mom's abdomen hair starts shedding.
You can now feel the puppies moving around inside mom when she is at rest. The puppies can be born safely now.
Puppies continue to grow.
An excellent site on this is:
Hope this was what you were looking for.