Depending on which method to calculate the gestational age, the third week of the gestational period has different signs. According to the obstetric method, when the doctor counts the period from the beginning of the last menstruation, in the third week the egg is fertilized. It contains a complete chromosome set, capable of rapid division.
According to the embryonic method, when the period is counted from the day of fertilization of the egg, it has already begun intensive division, and the delay in menstruation is 6-8 days.
What happens at 3 weeks in the female body?
If fertilization did not occur in the second obstetric week, it is carried out during this time period. The unique composition of chromosomes determines the gender of the unborn child, its characteristic features: the type of nervous system, character, physique, height, eye and hair color, and many other features that make a person a unique creature.
Immediately after fertilization, the egg (now called a zygote) begins to divide. Simultaneously with the division process, it moves through the fallopian tubes into the uterine cavity. Under the influence of hormones, the endometrium of the uterus is in a state in which implantation of the zygote is carried out with a high probability.
The implanted zygote is called a blastocyst, its cells are intensively and continuously dividing. After a short time, a cavity with an embryonic disk inside is formed in the blastocyst. At the end of the 3rd week of the obstetric period, the disk is transformed into a cylinder with unequal ends. At one end of this formation, the head of the embryo is formed, the other end is transformed into a tail. It can be considered that the laying of the main organs and systems of the future fetus has begun.
Embryo parameters at 3 weeks of obstetric gestation:
Weight – 2-3 micrograms;
Growth – 0,15-0,2 mm;
The number of cells is about 250.
The process of fixing the future embryo in the uterine cavity takes about 40 hours. The blastocyst must produce a special immunopressor protein so that the woman’s body does not perceive foreign cells as a threat. If the protein is not released, the immune system will perceive the cells of the father of the unborn child as an element dangerous to the body and will not allow the blastocyst to gain a foothold in the uterine cavity.
The blastocyst consists of an outer layer, from the cells of which the placenta, amniotic sac and umbilical cord will form, and an inner layer – the basis for the formation of the embryo. The importance of this period of pregnancy can not be overestimated. If, during the laying of the most important organs of the unborn child, a woman does not part with bad habits, takes medication, eats improperly, does not strive for the correct work and rest regimen, these circumstances can be fatal and affect the course of pregnancy.