By now you have positively confirmed you are pregnant. If not a lot of things happening will make you very suspicious. A classic feeling of nausea and an increase in the frequency of wanting to pee are common. Some women just feel strange sensitive and moody.
The fifth week marks the start of the embryonic period. The baby’s body systems and structures, such as heart, brain, and spinal cord begin to form. The baby’s heart starts beating at a steady rate even though this may not be detected by a vaginal ultrasound for one or two more weeks. Along with these developments, the placenta also starts to develop.
You are now five-week pregnant and only seven more months to go.
You’re Baby in Week Five
Find out what’s happening with your growing baby’s fetal development during its fifth week of pregnancy.
At this stage, your baby is thinner than a grain of rice and just a little bigger. It is now less round and more like a curved tube. One end of this tube will in time form your baby’s head while the other end will form the bottom. In between these two ends, the spinal cord is being formed. There will be a series of bumps along this tube which will form your baby’s back. This will eventually form the baby’s central nervous system.
The baby is being nourished by a pear-shaped yolk sac filled with fluid. The baby’s primitive heart circulates the blood to the wall of the yolk sac and back. The heart is only a small tube at the moment but in a week’s time will start to develop left and right chambers.
There are other developments taking place. The baby’s brain will divide into two lobes by the start of the second month of pregnancy. The respiratory system will appear as a groove behind the face. This will keep growing downward as the baby develops, branching 23 times along both sides of the body as the lungs finish forming. The arms and legs are tiny buds, and minuscule, paddle-shaped hands may even show finger buds. Your baby will finally be visible to the naked eye.
This week, an ultrasound will show the baby as a tiny white image tucked within the gestational sac. It will also show the heart is beating!
The baby is still a cluster of rapidly developing cells. These cells are becoming even more and more organized. The cells are formed into a flat disk with three layers. The first layer will become your baby’s brain, nerve tissue, and her skin. From another layer, she’ll develop lungs an intestine. And from the remaining layer, her heart, blood vessels, kidneys, genitals, bone, and connective tissue will develop.
This tiny disk contains all the elements the embryo needs to become a fully formed baby. Using an ultrasound machine the sonographer can measure this cluster of cells. The distance between the embryo’s crown — or the top of the “head”– and the rump, or “bottom.” This measurement called the crown-rump length, or CRL will help pinpoint the due date of your baby.
Ultrasound checks are normally not done at this stage. In the fifth week, the embryo’s heart will begin to flutter. The heart is simply a tube and it is the first organ to begin working at this stage. The heart will pulse at about 90-100 beats per minute. By the time the embryo reaches 8 weeks, the heart rate increases to about 120-160 beats per minute. This heart rate will stay in this range for the rest of the pregnancy. Although the heart is beating, it is not possible to hear it for another few weeks.