This is the time during three weeks pregnancy, when many expecting mothers are not even aware of the fact that a new life is taking shape in their bodies but the week by week calendar of pregnancy has already entered the third week of first trimester pregnancy. The one required sperm has hit the right spot on the female's fallopian tube. The thus fertilized egg is busy expanding in the fallopian tube to become a zygote. The next stage entails shifting of this multiplied zygote into the uterus where it rests under the shed of thick uterus walls for the weeks of pregnancy that follows.
The entire process as mentioned takes about 8 - 12 days. Slight pregnancy spotting is expected in few cases or pregnancy third week, which is very much normal in the initial cycle and therefore, can be ignored. In case if more than one egg is fertilized or one egg divides into two, twin pregnancy is expected. The thus formed zygote or your cherished baby is just about 0.1 - 0.2 mm during this phase of section of week by week pregnancy.
Well, you might sleep over the new changes that would soon be visible to all around, your body however, is cautious enough to take appropriate steps to help the new one nurture in your womb. The much-required early Pregnancy Factor Protein is already being produced. With time this natural caretaker i.e. your body further takes other vital steps for healthy development like forming a water tight sac known as amniotic sac to cushion the embryo, shaping up of the placenta, etc.