10 Stages Of The Baby's Heart: From The Beginning To Birth

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Remember the day when you first saw your baby’s tiny little heart beating away in the ultrasound? Wasn’t it the most adorable feeling? However, it would have looked nothing like the shape of the heart that we know of. Once the egg is successfully fertilized, it takes nearly 4 weeks before the heart starts developing within the zygote. That brings us to the most important question – how does the baby’s heart develop in the mother’s womb? Let us break it down into stages to let you know how –

In This Article

1. Specialized Specks Of Cells

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Soon after fertilization, as a ball of cells begins to develop, some of them get reserved for heart and blood cells formation. These cells soon begin to form three layers – ectoderm, mesoderm, and endoderm. The mesoderm contains the root to all blood vessels and muscles. Since the heart is primarily a muscle, its development starts from mesoderm (1).

2. The Tube Formation

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At Week 3 itself, as the brain and spinal cord begin to form in the shape of a tube, so does the heart. The cardiac tube is initially cranial at the time of development as it originates within the neural folds (2).

3. The Myocardial Tube Development

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During this stage, the developing heart positions itself centrally within the embryo and takes the shape of an inverted Y. The marking studies have often suggested that the arms of the Y eventually turn out to be the atrial chambers whereas the stem of the Y is believed to develop into the left ventricle (3).

4. The First Heart Beat

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At Week 4, the fetal brain and spinal cord are rapidly developing. Since the heart is latched to the neural tube, it starts developing too. Soon, by the time you reach Week 4, the heart starts beating (4). However, the lungs are yet to be formed.

5. The Elongation Of Heart Tube

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As the fetus begins to grow in size, the addition of new cells elongates the primary tube of the heart. With this elongation, a major part of the tube, which was so far restricted in movement, breaks away partially and liberates itself. Once it gets liberated, the tube immediately bends towards the right to initiate looping (5).

6. Looping Of The Heart

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At this stage, as the tube loops and bends towards the right, it takes the shape of an S. The ventricular loop inlet and outlet are also formed. This outflow tract feeds the arteries that originate from the aortic sac (6).

7. Formation Of Heart Chambers

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At this phase, the heart finally starts developing the chambers that we usually associate it with. It now has atrial as well as ventricular components together with outflow tracts. The atrioventricular canal separates the atrial and ventricular components. From here on, the atriums and ventricles start developing substantially (7).

8. The Fetal Heart Circulation

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Before the lungs develop, and even after they do in the womb, the fetus continues to breathe oxygen through the mother. Therefore, there is a marked difference in the way the heart functions in the fetus. In the absence of lungs, the job of supplying oxygenated blood to the heart is done by the placenta (8).

9. The Shunts Close

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Inside the womb, as the baby breathes through the placenta, the blood from the fetus’ heart is redirected to different organs of the body through the shunts. These shunts are known as patent foramen ovale. Once the baby is born, the function of these shunts is no more required as the lungs come into the picture. Although it’s generally not predictable, these shunts normally close after birth (9).

10. The Lungs Expand

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Once your baby is born, it still has some of the oxygen reserved until the umbilical cord is cut. And the new environment, including the temperature changes and lack of oxygen, triggers the baby to cry and take the first breath. This expands the lungs and from here on the baby’s lungs begin to function normally. Your baby’s heart now starts blood circulation with oxygen provided by the lungs (10).

Isn’t it amazing and truly unbelievable how a tiny speck of cell forms into a life-giving organ, the heart? We are sure now you would look at your little one from an amazingly different perspective. A miracle, did we hear? We couldn’t agree more.

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