The embryo is now undergoing a particularly critical developmental phase. The head and body of the embryo are clearly distinguished from one another.
All the major internal organs, the bones, muscles, blood vessels and blood have started to form. This progressive cell differentiation means that the embryo can no longer easily compensate for any damage that may occur.
The embryonic heart has formed and is pumping fluid through the tiny blood vessels. This simple beating action can be viewed using a high-definition ultrasound device. It creates a stable circulatory connection between the mother and the embryo via the placenta. The placenta now takes on an important function: it is used for the exchange of oxygen and nutrients. However it also serves as a barrier and protects the embryo from harmful substances.
The development of the central nervous systems is particularly important. The neural groove closes and forms the neural tube, which later develops into the brain and the spinal cord. Any disruptions or damage during this stage can lead to a malformation (neural tube defect). Folic acid supplements or special multivitamin supplements for pregnant women can significantly reduce the risk of neural tube defects. That is why you should start taking these kind of supplements as soon as possible – if you are planning to become pregnant, you should start taking them months in advance.
Your last period started over four weeks ago, so it’s late. If you are pregnant, the pregnancy hormone hCG will prevent any other egg cells from maturing. That is why you will not ovulate or menstruate again until after you give birth.