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Your Pregnancy during the First Trimester Week by Week

The first trimester of pregnancy is one of the most interesting periods of time from the woman`s life. Her body goes through a series of rapid changes for which her mind has to adapt quickly.

First Trimester Week by Week

Let`s take a look at some of the most basic aspects taken week by week that involves the first pregnancy trimester.

Table of Contents

Week 1

  • In the 3rd – 4th days, the fertilized egg will reach the uterus through the fallopian tube.
  • In the 5th – 9th days, the fertilized egg will be implanted in the uterine wall and will start to feed.

Week 2

  • In the 10th – 14th days, the first pregnancy symptoms may appear: the menstruation will stop, the appetite may start to grow, breasts will increase in size and morning sickness might start to appear. All the changes during this period start to appear because of the progesterone hormone produced at first by the ovaries and then by the placenta.

Week 3

3 levels of cells will start to develop:

  • The ectoderm cells, from which the organs for smell and the nervous system will develop.
  • The mesoderm cells, from which the circulatory, muscle and bone systems will develop.
  • The endoderm cells, from which the glandular and digestive systems will develop.

A layer of special cells from the uterus will form the placenta and the nutritive substances through which the new organism will feed. The rapid development of the new organism from this period will make him very vulnerable.

Week 4

  • After 1 month, the embryo is 10.000 times bigger than the original fertilized egg and is developing fast.
  • The embryo has a length of 0.5 – 1 cm and is developing with around 1 mm/day.
  • The eyes and the face`s organs (nose, month, ears) start to develop.
  • The heart starts to beat with 65 beats per minute. A circulatory system formed from veins and arteries will start to develop.
  • The liver, kidney and digestive tube start to develop.
  • The placenta forms a barrier which allows for the mother`s blood to remain separate, but in the same time it allows passage for oxygen and food to the new organism.

Week 5

  • The embryo is now 2 -3 mm in length and is deeper implanted into the uterine wall.
  • Around it has been formed the amniotic sac.
  • The first signs of the arms and legs start to appear.

Week 6

  • Since the 40th day the bioelectric activity of the new fetus`s brain can be registered.
  • Since the 45th day the electrical heart activity can be registered.
  • Since the 6th week, the liver start to take control in producing the blood cells.
  • The brain start to control for the movement of muscles and organs.

Week 7

  • Since the 7th week, the fetus starts his arm and leg movement.
  • The fetus measures around 15mm in length, weighs around 2g and start to take the shape of a human being.
  • Since the 7th week, the jaw starts to form, including the roots for teeth.
  • This week it will be developed over 100.000 new nerve cells per minute.
  • The fetus starts to have reflexes, is able to react to touch and feel pain.

Week 8

  • The fetus measures around 2 – 4 cm and weighs around 13 g.
  • The stomach produces gastric juices.
  • The kidneys starts to function in relation with the nervous system.
  • The groups of muscles function in relation with the nervous system, so the fetus can make a fist or grab his umbilical cord.
  • The fetus is floating through the amniotic liquid, being protected by pressure or shocks.

 Week 9

  • The fetus will be able to bend his fingers.
  • This skin can respond to tactile stimulation.

Week 10

  • The uterus will double its size.
  • The fetus is able to have his eyes half opened, can swallow and can develop a frowning face.

Week 11 & 12

  • The face already takes the form of a human being.
  • The movements of the muscles become more coordinated.
  • The fetus has 6cm in length and weighs around 30 g.
  • From this age his fingerprints can already be noticed, which won`t change for his entire life, more evidence that the fetus has become a human being.
  • His liver, bone marrow or spleen are fully developed to produce blood cells.
  • His blood type can already be determined.
  • The fetus swallows and breaths amniotic liquid to develop his respiratory system, sleeps, hiccups, frowns his face, moves his eyeballs, touches with his hands and legs, sucks his thumb or urinates.
  • The development of his sense of balance makes his moves more coordinated, so he can even roll.
  • He senses heat, noise or light.
  • He sleeps, wakes up and moves his muscles more often – he turns his head, bends the toes from his legs and opens his mouth.

During the first pregnancy trimester, because of the rapid process of development and changes that occur in the shapes of the body, the skeleton needs to be rather soft. At the beginning, it`s formed from soft bone cartilage, which later it ossifies and turns into the real bone.

Image courtesy of keepvitality.com

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