Having reached the stage of eight weeks, our embryo no longer has the consolidated form that it presented during the first weeks. We can clearly see the face, neck and limbs with differentiated fingers and toes. And the body in the process of becoming begins to move. At nine weeks, the human embryo is no longer alone, it is already a fetus.
This embryonic stage begins at the 9th week and ends with birth. During this 32 week period, the fetus will grow in inches and grams and its organs and tissues will mature.
He is no longer an embryo, but a fetus, he has a human form. His head, still oversized in relation to his body, grows more slowly. His eyes are thinly lidded, his eyes still on either side of his head, he opens and closes his fists, wiggles his toes, his skeleton begins to harden. © SEBASTIAN KAULICKI / SPL /AFP
The fetus is able to swallow, swallow the amniotic fluid, in which it still bathes freely. He explores his sense of touch: he has opened his hands, his mouth and can suck his thumb. The reproductive organs are sufficiently developed to determine the sex of the fetus, but are not yet fully developed. A female fetus develops between 2 and 5 million ovarian follicles. Their number will continue to decline until birth. A girl at birth has about 500,000 follicles in both ovaries of the fetus. At birth, only 300 to 400 of these follicles will remain. In boys, the glans and foreskin are forming.© SEBASTIAN KAULITZKI / SPL /AFP
If it came out prematurely, our fetus would have a chance to survive outside. Only his respiratory system, his lungs are not yet mature enough. His movements were more visible to the mother for several weeks. Her hiccups too! He fidgets when his mother falls asleep and seems to be lulled by his mother’s daytime activities. The phases of sleep and wakefulness alternate.© SEBASTIAN KAULITZKI / SPL /AFP
We are coming to the end of pregnancy. The space inside the pocket has become more limited. Head is the widest part of the body fethus, but the membrane between his cranial bones, the fontanelle, allows for the deformities necessary to pass to the exit. This skull has more or less a lot of hair depending on the person, while the fluff has started to disappear. The same applies to the white, viscous and waxy substance that keeps the skin in its liquid medium, the original lubricant. It also increased his fat reserves. © SEBASTIAN KAULICKI / SPL /AFP
Growth is determined by several mechanisms
The uterus is not always what it seems: a warm cocoon or a quiet respite before bursting into this world. Growth within the growing uterus is regulated by genetic, hormonal, and environmental mechanisms.
- Genetic factors tend to aggravate during the first half of pregnancy: obesity, birth weight, and maternal height affect fetal growth. It has been recognized for many years that a mother’s health directly affects the health of her unborn child.
- Hormonal mechanisms are critical throughout pregnancy from egg implantation through the fetal and then fetal phase to delivery.
During the embryonic phase, the most important are:
– Progesterone, which acts on the lining of the uterus. After the egg is implanted, it relaxes the muscles of the uterus to prevent contractions during pregnancy.
– The same is true for estrogen secretion. They affect the growth of the uterus, the development of the fetus and the increase in blood volume. In the expectant mother, they also cause breasts to swell in preparation for breastfeeding, stimulate melanin production, and weaken ligaments and tendons.
– Thyroid hormones, necessary for the bone and nervous systems of the unborn child, are brought to him by the mother, when he is only a zygote, then the embryo. During the fetal stage, the thyroid gland gradually matures and takes over from the mother at the end of the first trimester of pregnancy.
Initially secreted by the mother, these hormones will be produced by the placenta from the second trimester or, in the case of thyroid hormones, by the fetal thyroid.
- Environmental factors must also be taken into account. The list is long: the physical and mental health of the mother (including the well-studied maternal stress).), diet, sleep, physical activity, substance use (tobacco, alcohol, drugs).
If we look at the mother’s diet, we have long ago combined the idea that it plays a predominant role in shaping food tastes and reluctance to have an unborn child. Maternal vitamin deficiency can lead to developmental delays and malformations. Some foods that should be avoided during pregnancy and vectors of serious diseases (toxoplasmosis, listeriosis) pose a risk to the development of the fetus.
But a growing body of evidence suggests that a father’s diet before conception also has an effect. What a father eats may be associated with the occurrence of certain diseases in his children. Thus, we were able to link the diet of fathers and the occurrence of type 2 diabetes in their daughters. A carefully monitored folic acid deficiency in expectant mothers can also be detrimental to fetal development if the future father suffers from it.
This mechanism that affects the future of the fetus is called epigenetics. The epigenetic heritage of ancestors, parents, grandparents can influence the future of the unborn child. And it’s not just about food, but also about the lifestyle and accidents of this ancestor.
Contaminants can also alter and affect fetal growth. INSERM confirms that pregnancy and early childhood are more vulnerable to the presence of a toxic event or agent. Thus, it has been found that air pollutants can have a harmful effect on the placenta, affect birth weight, or cause lifelong disability: learning disabilities, a high prevalence of certain diseases, in particular cardiovascular diseases, or even obesity. It can also be substances present in food, cosmetics, medicines. Back in 2016, a Public Health France study identified a wide range of endocrine disruptors in the urine of thousands of women giving birth: bisphenol A, phthalates, pyrethroids, dioxins, furans, PCBs, flame retardants and perfluorinated compounds.
The “cocktail effect” of these substances, i.e. simultaneous exposure to several of these products, will entail a risk to the sexual and reproductive system of the unborn child. We are talking about titanium dioxide or E171, a food additive whose impact on the health of the fetus has yet to be proven, but whose ban in France has been extended from 2020. Even before it is born and expelled from the mother’s body, the fetus, the future newborn, will experience a development that will be nothing more than a leisurely stroll.