The 3 phases of intrauterine or prenatal development

During the normal nine months of pregnancy, the fertilized egg develops by following a series of stages: pre-embryonic, embryonic, and fetal. The concept of "prenatal development" or "intrauterine" is used to refer to these three stages as a whole, although the passage from one to another is progressive and the distinction is of a practical.

In this article we will analyze the process by which the embryo develops into a baby throughout the stages of intrauterine development. Although childbirth is understood by many people as the milestone that marks the beginning of growth, the postnatal development is largely a natural continuation of that which takes place in utero maternal.

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Main phases of intrauterine development

The chain of biological stages that go from the fertilized egg to the formation of the fetus are as follows.

1. pre-embryonic period

The preembryonic phase of intrauterine development, which

Sometimes it is also called “germinal phase”, is the shortest of the three: it lasts from fertilization until the second week. Since pregnancy is usually not detected until after a month or so, the woman is not yet aware of fertilization.

During this period of time, the fertilized egg (known as a zygote) travels down the fallopian tube. fallopian until it reaches the uterus, where it implants approximately between the eighth and tenth day of life. gestation. When this happens, the placenta begins to develop.

During this process the zygote repeatedly self-replicates. this division gives rise first to the morula and later to the blastula, names given to the set of cells that will give rise to the embryo based on its degree of development.

During the first week, the future embryo does not grow because it is contained within the zona pellucida, a layer of glycoproteins. Subsequently, already implanted in the uterus, it will begin to develop rapidly from a process of cell differentiation.

The presence of external harmful agents (teratogens), such as infections, diseases of the mother or certain substances, can cause abortions spontaneous or not affect the pre-embryo at all if it occurs during this phase of development prenatal.

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2. embryonic period

From the third week of gestation, the embryo is known as a gastrula. The cell layers of the blastula have differentiated to the point of giving rise to the three structures from which the baby's body will be formed: the ectoderm, the mesoderm and the endoderm.

Throughout intrauterine development the ectoderm will give rise to the nervous system and the epidermis. From the mesoderm will arise the bones, the muscles and the circulatory system. For their part, the cells of the endoderm will differentiate as cells of the respiratory and digestive systems.

The embryonic period is considered to last up to eight and a half weeks of gestation; Although there is no specific point that distinguishes when the embryo becomes a fetus, shortly after two months it is already possible to identify a future baby.

During this phase the embryo acquires basic physical traits, both internally and externally. Thus, the head, face, limbs, body systems and internal organs begin to develop, and the first movements also appear.

Intrauterine development follows the cephalocaudal and proximal-distal principles; this means that the upper parts of the body mature first, as well as those closest to the spinal cord. Broadly speaking, this pattern will be maintained in growth during the first years of life.

in the embryonic period the future baby is very vulnerable to teratogens; Since the fundamental organs and systems are developing, harmful agents can cause irreparable damage to them by altering their normal growth.

3. fetal period

In the fetal stage the development of the fundamental structures of the body, which were already present at the end of the embryonic period, continues and is consolidated. It is the longest stage of intrauterine development, encompassing from the ninth week until delivery.

Biological sex is manifested during the fetal period through the progressive differentiation of the sexual organs. However, it is determined from fertilization, since it depends on whether the successful sperm carries an X or Y chromosome; in the first case the baby will be a girl and in the second a boy, although there is some variability in this regard.

In this period the body of the fetus prepares for survival outside the womb. Among other aspects, the immune system is reinforced by obtaining maternal antibodies and a layer of fat appears on the skin with the function of keeping the body at a stable temperature and adequate.

The effects of teratogens are milder in the fetal than in the embryonic period. The tissues of the body are already formed, so the potential interference in their development is less, although it is still It is common for growth retardation and chronic defects of varying severity to occur due to teratogenic.