Baby development

The first day of pregnancy is considered to be the first day of the last menstruation because most women cannot know for sure when their most fertile day was, and it is also not possible to know on what exact day the fertilization occurred since sperm can survive up to 7 days inside the woman's body.

From the moment of conception, the woman's body begins a process of countless transformations, the most important of the first days being the thickening of the lining of the uterus, called the endometrium, to ensure that the baby has a safe place to develop.

Moment of conception

3-week embryo

Fetal development in the first 3 weeks

After conception, the developing embryo sends a message to the pituitary gland of its existence, through the hormone Beta HCG, suppressing the next menstruation and keeping progesterone levels high throughout pregnancy.

Since the placenta does not yet exist, the embryo behaves independently of the mother, however, it is already dependent on the mother's body to receive the necessary shelter for its development. The placenta usually develops around 12 weeks of gestation, when the baby's needs become more demanding, requiring a greater amount of blood, oxygen and nutrients.

Find out more about how conception happens and what happens in the woman's body.

How big is the baby

The embryo is still very small, weighing only 1g, being smaller than the head of a pin.

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First signs of pregnancy

In the first 3 weeks of pregnancy the woman's body begins to adapt to generate a baby. After the sperm enters the egg, a moment called conception, the cells of the father and mother come together to form a new tangle of cells, which within about 280 days, will become a baby.

In these weeks, the woman's body is already producing several types of hormones important for pregnancy, mainly beta HCG, a hormone that prevents a next ovulation and the expulsion of the embryo, stopping the woman's menstrual cycle during pregnancy.

In these first weeks, women rarely notice the symptoms of pregnancy, but the most attentive ones may feel more swollen and sensitive, becoming more emotional. Other symptoms are: Pink vaginal discharge, Colic, Sensitive breasts, Tiredness, Dizziness, Sleep and headache and Oily skin. Check out the first 10 pregnancy symptoms and when to take the pregnancy test.

Your pregnancy by trimester

To make your life easier and you don't waste time looking, we have separated all the information you need for each trimester of pregnancy. What quarter are you in?