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The baby already has some of its own blood vessels and blood begins to circulate.
A string of these blood vessels connects the baby and mother, and will become the umbilical cord.
This means that in the first two weeks or so, you aren't actually pregnant – your body will be preparing for ovulation as usual.
The egg begins as a single cell, which divides again and again.
Many early miscarriages (before 14 weeks) happen because there is something wrong with the baby.
There can be other causes of miscarriage, such as hormone or blood clotting problems.
Defects in the "head end" lead to anencephaly, when the bones of the skull don't form properly.
At the same time, the heart is forming as a simple tube-like structure.