Timeline

The progress of human development can be mapped onto a linear timeline such as the one below. Drag the slider along the timeline to see how development progresses, and if you want to know more about a specific time period in more detail then click on the picture displayed for that stage. Alternatively, click one of the links to the left to read through the timeline chronologically.

  • Week 1

    > Fertilisation occurs

    > Cleavage occurs

    > Implantation begins

  • Week 2

    > Implantation completes

    > Trophoblast differentiates

    > hCG production begins

    > Amniotic cavity forms

    > Primary umbilical vesicle forms

    > Extraembryonic mesoderm forms

    > Lacunar networks form

    > Primary chorionic villi form

    > Chorionic sac forms

  • Week 3

    > Gastrulation occurs

    > Notochord forms

    > Neurulation occurs

    > Somites begin to form

    > Intraembryonic coelom forms

    > Primary chorionic villi mature

    > Heart begins beating

  • Week 4

    > Folding occurs

    > Pharyngeal arches begin to form

    > Rostral neuropore closes

    > Brain begins to form

    > Upper and lower limb buds form

    > Otic pits form

  • Week 5

    > Caudal neuropore closes

  • Week 6

    > Limbs and hands form

    > Auricular hillocks form

    > Umbilical herniation occurs

  • Week 8

    > Movements begin

    > Ossification begins

    > Facial features begin to form

  • Week 12

    > Erythropoieses moves to spleen

    > External genitalia form

    > Urine production begins

  • Week 14

    > Limbs begin to move

    > Hair patterning is determined

    > Ovaries fully differentiate

  • Week 18

    > Vernix caseosa appears

    > Lanugo appears

    > Hair begins to appear

    > Brown fat forms

    > Uterus forms

    > Testes begin to descend

  • Week 24

    > Rapid weight gain

    > Fingernails form

    > Surfactant secretion begins

  • Week 28

    > CNS matures

    > Subcutaneous fat forms

    > Toenails form

    > Erythropoiesis shifts to bone marrow

  • Week 32

    > Skin turns pink and smooth

  • Week 38

    > Birth