Pregnancy or pregnancy is the entire period of growth and development of the embryo within the woman.

For it to happen, it is necessary that the female gamete (egg) be fertilized by the male gamete (sperm), giving rise to the egg or zygote .

After several mitoses, the zygote is transformed into the embryo and implanted in the wall of the uterus, a process known as nidation . Pregnancy starts from the nest and ends with the birth of the baby.

The normal gestation time is 40 weeks or 9 months , counted from the last menstruation. When the baby is born before the expected date, it is called premature .

Pregnancy Weeks

Scheme showing in which fetal period the organs develop.

The 40 weeks of pregnancy are divided into 3 semesters . After the eighth week of gestation, the baby is no longer considered an embryo and is called a fetus . It is during the 1st quarter that all of its important organs develop.

From the 4th week of pregnancy, common symptoms begin to appear in early pregnancy, such as nausea, vomiting, tiredness, pain in the breasts and enlargement of the breasts. These symptoms are caused by the hormone Chorionic Gonadotropin, which is produced by the embryo.

Near the 7th week of pregnancy, a plug of mucus will develop in the cervix to prevent contact of the uterus with the external environment and provide more protection to the baby.

In the second trimester , the fetus grows rapidly and already has a recognizable human appearance. The woman’s heart rate and blood pressure increase to meet the fetus’ needs.

In the third and final trimester , the baby’s organs mature and increase the fetus’ chances of survival.

See also: Blood pressure

Hormones and Pregnancy

When the embryo is implanted in the wall of the uterus, it starts to produce chorionic gonadotropin , a hormone that prevents the rates of estrogen and progesterone from decreasing.

Thus, menstruation does not happen, this being one of the first signs of pregnancy.

Pharmacy pregnancy tests detect the presence of chorionic gonadotropin in the urine.

Chorionic Villi

These are projections that cover the surface of the amniotic sac and penetrate the uterus. Gaps are formed around it, through which maternal blood circulates.

Thus gas exchange occurs between the blood of the embryo, which circulates in the villi, and the maternal blood, which circulates in the gaps.


Most chorionic villi regress after the second month of pregnancy, except in the area where the villus penetrate the uterus most deeply, resulting in the placenta.

The embryo’s communication with the placenta takes place through the umbilical cord.


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