Prenatal Development Timeline

By: Kaityn Hendrix


In fertilization, one of the eggs travels down from the ovaries to the uterine tube. A sperm swims all the way up to the uterine tube in order to fertilize the egg. Once the sperm penetrates the outer membrane of the egg, the genetic material of both combines to create a new cell, which begins to rapidly divide.

*The moment fertilization takes place, the baby's genes and sex are set in place.


Within 24 hours of fertilization, the egg will begin dividing rapidly and will continue to travel down the uterine tube to the uterus. It will then attach itself to the lining of the uterus.

*hCG- A pregnancy hormone detected by pregnancy tests 3-4 weeks from the first day of your last period.

Cleavage, Blastula Stage, and Gastrulation

A zygote will go through cleavage (cell division) multiple times in order to create a little ball of cells, called a blastula. This blastula will eventually divide into two different layers. These layers are the inner cell mass (eventually the embryo) and the outer layer/trophoblast (eventually the placenta). Next is gastrulation. In this stage, the blastula will fold on itself to create three germ layers called the ectoderm, mesoderm, and the endoderm.

*The morula is created about 96 hours after conception, and is known as a collection of about 30 cells.

4 Weeks

  • This is the beginning of the embryonic period
  • This is the time where the embryo consists of the two layers; the epiblast and hypoblast
  • The amniotic sac, amniotic fluid, and yolk sac are all present

5 Weeks

  • At this time, the embryo is made up of three layers- Ectoderm, mesoderm, and endoderm. These will be what form all of the babies organs and tissues later on.
  • The neural tube, nerves, and backbone are starting to develop in the top layer.
  • The embryo's skeleton begins to develop
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6 Weeks

  • The baby has its first heartbeat and the heart is beating about 100 to 160 times a minute
  • The nose, mouth, and ears are beginning to take shape and the lungs and intestines are beginning to develop.

7 Weeks

  • The umbilical cord has blood vessels to carry oxygen and nutrients back and forth to the baby now.
  • Both hemispheres of the brain are growing.
  • Hands and feet are starting to show up on the arms and legs

8 Weeks

  • The hands and feet are starting to develop webbed fingers and toes.
  • The baby is beginning to move around, but he is still too small and the movements too fine to be able to feel them

9 Weeks

  • The embryonic tail is now gone
  • The internal sex organs are there but are not distinguishable
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10 Weeks

  • This marks the beginning of the fetal period where the babies tissues and organs will rapidly grow and mature.
  • The vital organs of the baby are functioning

11-14 Weeks

  • 11: The baby can now hiccup
  • 12: The baby's reflexes have developed, so he can now open and close his fingers and curl his toes
  • 13: The baby now has fingerprints
  • 14: The baby can squint, frown, and suck his thumb

15 Weeks

  • You may be able to tell the sex of the baby with the use of an ultrasound!!
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17 Weeks

  • The skeleton of the baby changes from cartilage to bone (ossification)

18 Weeks

  • Myelin (a protective covering) is beginning to form around the baby's nerves