Pregnancy Week 6 – The Baby’s Progress

Pregnancy week 6 sees the brain becoming a lot more complex, forming into 3 separate ridges which will define the 3 different areas. These are the forebrain, controlling memory and thinking, the midbrain which co-ordinates messages and the hindbrain, regulating the beating of the heart, automated breathing and the spontaneous movement of muscle. It also has vesticles which are bubbles of liquid in a membrane-enclosed sac that store and transport information within a cell. The hindbrain is the first to mature.

Pregnancy Week Six – Developing Embryo

Skull, face and head continue to mature and widen and an oral cavity has appeared below the forebrain, known as the Stomodeum, which is the precursor to the mouth. The thigh, leg and foot plates are now distinguishable on the lower limbs with external swellings appearing on the sides of the head where the ears will form. The ureter tube that carries urine from the kidneys to the bladder has now formed and continues to lengthen.

Once you have reached the 6 week pregnant phase, cartilage foundations are laid down for the spinal tube and rest of the skeletal structure but the ossification (turning to bone) does not begin until around week 8 (the end of the ’embryonic phase’). This cartilage placement now makes the embryo visible in a scan. As there is no definitive bone structure in place yet, the pointed ‘blob-like’ head will still remain flopped downward towards the tip of the tail. There is a tube that runs from the point of the mouth to the tail that will later develop into the bowels and stomach.

The heart that only sprung into life a few days ago and is now beating, is still only a 2 vessel chamber that is ‘fluttering’ real fast but it will develop from 2 chambers into 4, but not quite yet, as the circulatory system is not mature enough for 4 valves. The heart is still bent in the shape of a “S” and when it finally divides into 4 chambers it will have two chambers called the “atria” that will receive blood to the heart and the other two “ventricles” that will pump blood out to the rest of the body. At the moment the heart is still only a little bulge, the size of a poppy seed, sticking out the front of the embryo and the curled up embryo itself is no larger than a grain of rice.

Although the embryo is still so small, amazingly, by pregnancy week 6 the beginnings of all the major organs are now almost in place with the lungs, pituitary glands and intestinal tract also in the growing stage, the liver will be the first part of the digestive system to begin working in the coming weeks. The embryo is still attached to the underdeveloped placenta by the beginnings of an umbilical cord in the form of a stalk and the placenta, at this stage, is still primitive in design so the life support and blood cells for the embryo will continue to be supplied by the yolk sac for the time being.

By the end of pregnancy week 6 your embryo will have an alien looking appearance with a over-sized head and small black plates (at the side of the head) where the eyes will form. These primitive looking eyes just look like little black bumps on the head during this week but will begin developing eye fibers and retina pigment. As the eyes begin to bulge they will develop eyelids over them that will then fuse together while the eye underneath begins its complex job of growing into fully fledged eyeballs. Over time the eyes will move closer together as the facial features begin to shape up and the eyelids will open for the first time around week 28.

Pregnancy week 6 will see your developing embryo measuring around 0.39” (10 mm) crown to rump.

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(See 6 Weeks Pregnant – The Mother’s Progress)


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