Fetal Development

  • Week 1

    Week 1
    The female goes through her final menstruation before giving birth. This is the very beginning of pregnancy.
  • Week 2

    Week 2
    One sperm cell meets the ovum in the fallopian tube. It penetrates the ovum, fertilizing it.
  • Week 3

    Week 3
    The 23 chromosomes from the sperm cell unites with the 23 from the ovum. The offspring is set as either a boy or a girl, depending on which chromosome, x or y, the sperm cell was carrying. The ovum travels down the fallopian tube while dividing itself.
  • Week 4

    Week 4
    The egg, now a blastocyst, moves into the uterus. It implants itself on the uterine wall. The blastocyst releases the human gonadotropin hormone, which is responsible for the signs of pregnancy and for making sure that the uterine walls stay in place.
  • Week 5

    Week 5
    The embryo develops rapidly. The placenta supplies the embryo with oxygen and nutrients. The brain and spinal cord begin to develop, along with the nerves.
  • Week 6

    Week 6
    The vital organs begin to form. The heart begins to beat. The placenta starts functioning.
  • Week 7

    Week 7
    The fetus begins to take proper shape. More organs begin to develop. The neural tube closes.
  • Week 8

    Week 8
    The limbs are stretching out. Facial structures are becoming clear. The pituitary gland develops and muscles start to form.
  • Week 9

    Week 9
    The embryo floats in fluid inside the amniotic sac. The fingersand toes are forming, though still webbed. There is limited flexion of the elbows and wrists.
  • Week 10

    The embryo is now referred to as a fetus. Organs, muscles, and nerves are working properly. The hands and feet are starting to look normal (not webbed).
  • Week 11

    Week 11
    The mouth and teeth are forming. The heart is almost done developing and moves blood away from the lungs. The eyelids are closed until week 27.
  • Week 12

    Week 12
    The brain is fully developed. The fetus can cry, suck its thumb, and feel pain at this point.
  • Week 13

    Week 13
    The fingerprints are formed. Muscles are coming into place and the fetus is making more movements.
  • Week 14

    Week 14
    The baby is peeing. The bones are strengthening. Hair is growing on the head.
  • Week 15

    Week 15
    Bones and muscles are still growing. The ears and mouth are almost done forming.
  • Week 16

    Week 16
    The fetus is able to breathe. The face is more defined and the muscles in the face are even more developed.
  • Week 17

    Week 17
    Fat is developing beneath the skin. The cartilage that forms the bones are starting to actually turn into bone.
  • Week 18

    Week 18
    The fetus may have normal sleeping patterns. Protective material forms around the fetus. Alveoli are developing in the lungs.
  • Week 19

    Week 19
    The genitals are developing and are distinct at this point. The legs are almost the right length and are moving a lot more.
  • Week 20

    Week 20
    The five sense are developing. The fetus is able to recognize sounds coming from outside.
  • Week 21

    Week 21
    Blood cells are now being produced by the bone marrow. The genitals of the fetus are further developed.
  • Week 22

    Week 22
    The fingernails are grown out. The eyebrows and eyelids are finished developing.
  • Week 23

    Week 23
    Color is coming to the skin. The pancreas is developing. The fetus is developing a sense of balance and direction.
  • Week 24

    Week 24
    The lungs are developing further. Taste buds have developed and the fetus can taste what the mother consumes.
  • Week 25

    Week 25
    The structures of the spine are developing. The structures of the hand have finished developing. The fetus is able to close its hands.
  • Week 26

    Week 26
    The fetus has started "breathing" inside the womb. It is able to suck on its thumb due to its more advanced muscle coordination. It also reacts to people touching the woman's stomach.
  • Week 27

    Week 27
    Hair continues to grow on the fetus. Its eyes are developing and may be able to see light from outside shing on it.
  • Week 28

    Week 28
    The fetus shows signs of dreaming. The lungs are much more developed.
  • Week 29

    Week 29
    The fetus may develop preference in foods because of its developed taste buds. Movement is limited but stronger due to the lack of space.
  • Week 30

    Week 30
    Blood cells are moving things around the fetus' body. The fetus has started storing essential nutrients. More fat is developing.
  • Week 31

    Week 31
    The respriatory and digestive systems are almost completely developed. The organs are almost all working and are now maturing.
  • Week 32

    Week 32
    The genitals are moving into place and are more distinct. The fetus is spending more time sleeping than moving around.
  • Week 33

    Week 33
    The fetus is breathing in amniotic fluid. It is becoming less fuzzy (with lanugo) and more hairy.
  • Week 34

    Week 34
    The fetus is repositioning itself in preparation of birth by putting its head down. The skin is smoothening.
  • Week 35

    Week 35
    The fetus is storing more fat but still does not have enough to sustain itself. Lung development is almost complete.
  • Week 36

    Week 36
    All organs but the lungs are mature. The fetus is likely in birth position and will not move much until birth.
  • Week 37

    Week 37
    The fetus is still growing inside the womb. At this point, the woman goes into labor, doctors will not delay the birth; it is within the normal birth range.
  • Week 38

    Week 38
    The fetus is finished developing. The body is now focused on gaining more fat.
  • Week 39

    Week 39
    The fetus is in position. Activity within the womb has decreased. Most of the lanugo is gone.
  • Week 40

    Week 40
    The baby is now due. The fetus is in position and ready to be born.