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human embryo at 6 weeks exactly

Your baby today

Here the back of the embryo can be seen lying over the yolk sac. The opening overlying the developing brain has now closed (left side of image) and this will be followed two days later by closure of the opening at the base of the spine (out of view).

By the end of this sixth week, one of your baby's major organs-the heart-is rapidly developing and circulating blood.

Your developing embryo may still be tiny, but is undergoing rapid and complex development.

The heartbeat is now more easily recognized on an ultrasound scan. The heart continues to form from a simple smooth tube which, as it becomes more muscular, loops, folds, and divides to form four chambers. On the left side the upper chamber (left atrium) takes in blood from the lungs. From here blood passes through a one-way valve (the mitral valve) into the main left pumping chamber (the left ventricle). This then pumps blood out of the heart to the body along the main artery (the aorta). On the right-hand side of the heart, the upper chamber (right atrium) collects blood returning from the body and passes it through a one-way valve (tricuspid valve) into the right main pumping chamber (right ventricle). This pumps blood to the lungs and the cycle continues.

At this stage of development, the circulation is very basic with the heart tube simply sending blood around the length of your baby. No blood travels from your baby's circulation to the placenta (see You are 10 Weeks Exactly).

Types of miscarriage

At this early stage, a common concern is that the pregnancy will miscarry. A miscarriage is the spontaneous loss of a pregnancy at any time up until the 20th week. After 20 weeks the loss is referred to as a stillbirth. The signs of a miscarriage are vaginal bleeding and periodlike cramps.

Unfortunately, there is nothing that you can do to prevent a miscarriage. In around 60 percent of cases, it is caused by a one-time genetic problem. Bleeding does not always mean that the pregnancy is being miscarried. Since not all miscarriages follow the same pattern, there are various terms to describe what happens:

  • A threatened miscarriage occurs when the pregnant woman experiences bleeding and possibly pain, but the baby survives.
  • An inevitable miscarriage occurs when there is bleeding and pain due to the pregnant woman's uterus contracting. The cervix opens, and the fetus is expelled.
  • A missed miscarriage is when the fetus dies but is not expelled. Surgery may be needed to remove it.

excerpted from:

Excerpted from Pregnancy Day by Day.
Copyright © 2008 Dorling Kindersley Limited.
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