By BSc, MSc (embryologist).
Last Update: 07/30/2014

In the sixth week of pregnancy you may start to have morning sickness, feel a bit tired and not in your normal self. This is due to the development and growth the baby is experiencing. Development is so important these weeks, as the complex systems of the organism start their formation, like the circulatory system, for instance.

The different sections of this article have been assembled into the following table of contents.

Most important changes

During this week, the primitive heart is formed, it has two blood vessels and starts beating.

The central nervous system has grown longitudinally, forming the prosencephalon, and causing the embryo to fold from the head to the tail, like drawing back to itself.

In the meanwhile, in the midpiece, an early intestine appears, which is the origin of the digestive system.

How does the embryo look like?

The embryo now looks a bit awkward, the head is huge, and has the primordium of eyes and ears. They are black stains that will eventually become the eyes and eras of the baby.

Two arm buds appear, the rough drawing of the arms, though they cannot be noticed yet, just like the legs.

The embryo is about 4 mm long by the end of this week.

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Authors and contributors

 Neus Ferrando Gilabert
Neus Ferrando Gilabert
BSc, MSc
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information about Neus Ferrando Gilabert

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