The three stages of pregnancy…a medical map to understand fetal growth and maternal transformations

Doctors divide the pregnancy period into three trimesters, each of which has different biological characteristics and changes affecting the fetus and mother. This division is not only chronological, but also constitutes an essential medical tool for monitoring the development of the fetus, assessing the health of the pregnant woman, and monitoring any potential risks.

First trimester of pregnancy (weeks 1-13)

It is considered the most sensitive, as the process of formation of the fetus’s basic organs begins, making it more susceptible to external factors such as medications, infections, and malnutrition. During this stage, the rate of miscarriage increases compared to the rest of the pregnancy.

During the first weeks, the central nervous system is formed, and the heart begins beating early, becoming the first organ to work in the fetus’s body. Limb buds also appear and facial features are initially formed.

By the end of the thirteenth week:
• Length: 7–8 cm
• Weight: 23–43 grams
• Size: approximately a lemon

Maternal changes: nausea and fatigue, mood swings, change in appetite, swollen breasts and frequent urination. Early medical follow-up and folic acid intake are essential at this stage.

Second trimester of pregnancy (weeks 14-28)

It is often described as the most comfortable stage, as disturbing symptoms subside and the mother feels more at ease. Organs continue to grow and begin to gradually perform their functions, bones become stronger, while the senses develop, especially hearing.

In this trimester, the mother feels fetal movement for the first time, which strengthens the emotional attachment to it.

By the end of the second trimester:
• Length: 35–37 cm
• Weight: 760–900 grams
• Size: close to a small pumpkin

Maternal changes: improved energy and appetite, abdominal expansion, mild back pain, and the appearance of pigmentation or stretch marks. Basic examinations are also performed to monitor the growth of the fetus and the health of the mother.

Third trimester of pregnancy (week 29 – birth)

This stage represents the final preparation for birth. The weight of the fetus increases rapidly, fat accumulates under the skin, the brain and nervous system continue to grow, while the lungs gradually develop. The fetus often assumes a head-down position in preparation for birth.

At the end of pregnancy:
• Length: 50–53 cm
• Weight: 3–3.5 kilograms
• Size: approximately the size of a large watermelon

Maternal changes: body heaviness, difficulty moving, shortness of breath, sleep disturbances, uterine contractions, and frequent urination. Doctor visits are increasing to monitor the fetus’s position and prepare for labor.

At the end of the journey, psychological and physical preparation remains an essential factor in safely crossing the birth stage and receiving the new baby with confidence and reassurance.

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