Embryonic period

Pregnancy begins with fertilization, which is the union of the male and female sex cells: the ovum and the sperm. At this time begins until the eighth week of.

Fertilization

For fertilization to occur, the woman must be in the ovulation period.

The ovulation It occurs when an ovum is detached from one of the ovaries, towards the middle of the. If at this precise moment, a sperm meets the egg in the fallopian tubes, fertilization can occur. The zygote It is the cell resulting from the union of the sperm with the ovum. It is a cellular structure that has all the genetic information necessary to develop and become a baby.

In fertilization it is already determined the sex of the baby. The egg only has an X chromosome but the sperm has an X or Y chromosome. Depending on the chromosome that provides the sperm, the baby will be a boy or a girl:

• X chromosome (ovum) + X chromosome (sperm) = GIRL
• X chromosome (egg) + Y chromosome (sperm) = CHILD

Each baby is unique, with its own DNA, which is made up of 46 chromosomes that will determine the baby's genetic inheritance.

Embryonic period

First week

The fertilized ovum divides for the first time 24 hours after conception, this is what we call zygote. During the following days it continues dividing and forms a ball of cells called a blastocyst. At 5 days, the blastocyst cells they separate into two groups: those that will form the placenta and those that will form the embryo (stem cells).

At the end of this first week, the fertilized ovum travels down the fallopian tubes to reach the uterus on the fifth day. It anchors in the wall of the uterus (implantation) at the end of the first week and there it will spend nine months.

The mother's womb has changed and has been adapted for pregnancy. The inner wall of the womb has become fluffy and thicker to favor the implantation of the blastocyst, necessary for the embryo to receive the necessary nutrients to grow.

Second week

The embryo that measures 0.2 millimeters begins to form. At this stage, the embryo has a rounded shape and is made up of two layers: the endoderm and the ectoderm. Cells multiply very quickly and acquire a specific function.

• The endoderm will form: skin, the inner lining of the respiratory and digestive system, the bladder, eardrum, thyroid, pancreas and liver.
• From the ectoderm: nervous system, skin, sense organs (eyes, ear, nose), nails, tooth enamel, pituitary, hair, mammary and sweat glands.

Third week

A third layer appears to the embryo, the mesoderm, from this tissue it will derive:

• The locomotor system (bones, muscles and cartilage)
• The vascular system (heart, veins and arteries)
• blood cells
• The genital and urinary system (except the bladder)
• The spleen and adrenal glands

Chorionic villi are formed that will connect with the mother's blood vessels. In this way, the embryo get the food and the oxygen needed to grow. On the other hand, organs such as the intestine, liver, kidneys and lungs are hollowed out in the trunk of the embryo.

Fourth week

The embryo grows one millimeter every day (it measures about 5 millimeters) and the development of:

• The extremities (arms, legs, muscles and bone)
• The heart of the embryo (mass of elongated muscle cells) begins to beat at approximately 22 days. This rudimentary heart will be in charge of distributing food and oxygen to all parts of the embryo so that it can grow. The embryonic heart beats at about 150 beats per minute.
• The digestive system it is differentiated into its different parts (esophagus, stomach and intestine).
• The sense organs appear, that is, the eye cavities and ears are formed.
• The neural tube, which will become the baby's nervous system (brain and spinal cord) and the spinal column.

Fifth and sixth week

The embryo takes on a human or baby form. It grows very fast and is now the size of a chickpea (5-6 millimeters). Its head is very large compared to the rest of the body and the limbs are very short:

• At face the eyes, nose, mouth and ears are perfectly distinguishable.
• The fingers not distinguishable yet
• The arms and legs they can begin to move at the end of the sixth week.

Seventh week

The embryo measures about 22 millimeters. The fabrics and Organs formed in the embryonic stage mature:

• The heart already has four chambers
• The palate and tongue begin to form
• The placenta increases in size to nourish the baby well
• He grows a lot and widens
• Nipples and hair follicles form
• Elbows and fingers can already be seen
• The digestive system and the urinary system of the fetus (which were the same structure) are separated
• Neurogenesis or production of neurons occurs.

At the end of this week the embryo measures 1 centimeter and these are the most delicate weeks of the baby because some medications, alcohol, nicotine, caffeine or radiation (such as X-rays) can affect it.

Eighth week

Officially ends on embryonic period and he the embryo is renamed fetus. The outline of all the organs of the future baby has been formed and it is already beginning to have a human form.

• The baby face He is already more defined and has eyelids, a nascent nose and an upper lip.
• The body lengthens, with more and more human form and the skin is translucent, so the skeleton can be seen. But the bones are not calcified, they are made of cartilage, that is, they are soft.

The embryo measures between 4 and 5 centimeters and weighs 9 grams. The circulation through the umbilical cord is very well developed.

What you should know:

• Before the fourth week the embryo has a round shape made up of different layers, endoderm, ectoderm and mesoderm.
• In the fourth, fifth and sixth weeks the embryo begins to develop limbs and take the shape of a baby.
• The embryo is called a fetus in the eighth week.

Remember that inMAPFRE We take care of your well-being and that of yours, that is why we offer you one with the best coverage so that you are always protected against any pathology or disease.

Dra. Esther Martínez García Pediatric Specialist