Between the fertilization of an egg by a sperm and the birth of an infant, nine months pass during which the embryo develops. From a single cell, over time he will become a fully formed human. From the first weeks of pregnancy, the first organs develop, like the heart. It will be one of the first organs to function in the embryo. “The formation of the heart, the embryo’s first functional organ, begins in the 2e week of intrauterine life“, explains Dr Houyel, pediatric medical cardiologist at Necker-Enfants Malades hospital in Paris in an article on embryology of the heart. “At 2 months of pregnancy, the definitive architecture of the heart is therefore established.. ”
“The training of the heart ends in the seventh week but it already has activity earlier “
Before the first trimester ultrasound, a first ultrasound (medical imaging performed using ultrasound) is offered by the gynecologist. This first ultrasound is said “dating “ because it aims to precisely date the start of pregnancy by measuring the embryo and to determine the number of embryos. During this appointment, it is already possible – but not certain – to hear the heartbeat of the fetus. “The training of the heart ends in the seventh week, but it already has activity earlier. We can hear it if we do an ultrasound around the ninth or tenth week“, explains Pr. Damien Bonnet, head of pediatric and congenital cardiology service takes care of all types of heart disease in children at the Necker-Enfants Malades hospital.
These heartbeats are twice as fast as an adult’s, in the range of 120 to 140 beats per minute. It also ensures that the pregnancy is not a clear egg, that is to say an egg which is born from the meeting between an egg and a sperm, but which has not resulted in the constitution of an embryo capable of development.
If the pregnancy goes smoothly, the baby’s heart can then be heard again at the three other ultrasounds scheduled before delivery. Listening to the heart of the fetus and then the baby also helps to ensure that he does not have a heart defect. At the maternity ward, when giving birth, the baby’s heart will be placed under monitoring and monitored throughout the delivery, in order to check that the baby does not get tired.
Development in stages
The heart of the embryo develops in stages in the womb of the mother. “The development of the heart begins in an embryo which is not determined, which looks like a kind of plaque. There are a number of signals that will tell certain types of cells to go to form the heart, that’s what we do. call the specification“, specifies the Prof. Damien Bonnet. “Morphogenesis begins, which consists of giving shape to an organ. Once it has been given its form, different structures are differentiated. This is the case for other organs too, such as the kidney or the liver.. “Right and left side, valves, venous and arterial poles … All these parts of the organ will become established over the days.
The heart is a special organ in embryology because it is an odd organ. “It is curious because the heart is not symmetrical, even if there is a right and a left in the organ. A large number of malformations are also due to confusion – either very early or later – in the definition of the shape of the right and the left. There may be abnormalities such as an aorta in place of the artery, inversions, holes that cause abnormal communications to exist within the organ“, explains Prof. Bonnet. These laterality problems give rise to asymmetry malformations. These are the most frequently hereditary malformations.”In the heart, large structures like the aorta are asymmetrical. There is a whole system that will first produce everything in duplicate, right and left. So we have two aortas at the start, then the one on the right side regresses. Then only the left one remains. ”
The formation of the heart then ends in the seventh week. “It ends with the development of the coronary system“, explains Dr Houyel. This coronary system will then form the Coronary arteries, so named because they are arranged in a crown around the heart. These arteries covering the surface of the heart, allowing to vascularize (to irrigate with blood), and therefore to nourish, the heart.
The other organs are also developing
During the first trimester of pregnancy, organogenesis starts the constitution of all the vital organs of the embryo, whether they are vital or sensory. All take their place and evolve during the growth of the fetus. Around 26 weeks of amenorrhea (amenorrhea begins on the first day of the last menstruation), the pulmonary alveoli form, the bronchi continue to divide. The lungs mature in the eighth month of pregnancy. The kidneys begin to form in the third month of pregnancy and become functional in the second semester. It is also during this period that the nervous system develops, with the multiplication of neurons, the organization of the cerebral cortex as well as the maturation of neurons.