You are now 5 weeks pregnant (21 days after conception), which is the beginning of week 6. This is when the woman's period is 1 week late. By now, you may begin to wonder if you are pregnant, or a pregnancy test may confirm that you definitely are! If you have irregular periods, or experienced an implantation bleed during weeks 4 or 5, you still may not realise you are pregnant yet!
During week 6, your baby's heart develops and first begins beating at around 24 days after conception. At this point, their heart is simply a long tube, rhythmically expanding and contracting. By the end of the 10th week their heart will have its various chambers and valves and be connected to a network of blood vessels supplying your baby's body. The baby's blood is initially produced by the yolk sac. Their blood stream remains completely separate from their mother's. They do not mix, with the baby often having a different blood type from their mother and/or father.
Your baby's neural tube now closes at the top (over their brain) and over the base of their spinal cord. This is an important time for the mother to have sufficient folic acidin her diet to support this process and avoid neural tube defects. During this week, small hand and feet buds start sprouting from your baby's upper and lower body (as shown in the image). Their body stalk elongates and starts to form 2 arteries and a vein inside, creating their umbilical cord, which will transport oxygen and nutrients from mother to baby and take away carbon dioxide and waste products from baby to mother. These are filtered through the placenta, along with many other substances that may be in the woman's system (such as nicotine, alcohol, vitamins, herbs or medications). You may wish to read lifestyle changes.
At this early stage, an ultrasound image may only show a gestational sac and a heart beat may not be detected yet. During the next week your baby becomes visible and is seen to be bent and curled in the shape of the letter C. This makes it difficult to measure them from head to toe. Therefore, ultrasonographers routinely measure the baby from the crown of their head, to the base of their back (or rump), referred to as the 'crown to rump length' or 'CRL'. By 6 weeks, your baby's crown to rump length is around 2 to 4 mm (or 0.08 to 0.16 inches).
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